More on wiring

[Jem]

Hi
sorry if this has been covered before, but I couldn't find a thread with it in...
UK RHD Sprint DHC.

so I am doing a full restoration and am looking at the wiring diagrams. My issue is the lack of fusing on the standard loom.
Yes there are the 2 glass fuses rated at 17/35A. These protect some of the circuits (horn/cigar lighter and wipers, washer, heater fan, indicators).
Lights, side/tail and headlights, and windows are unfused. The dashboard switches are rated at 15A which is lower than the fuse that is meant to protect them. Not good.

My major issues:

1. A fault on an unfused cable = fire risk as the cable will melt. So cables need protecting - or they will work until there is a fault, and then they will burn.
2. The brown/blue feed from the control box to the ignition switch is unfused.
3. The same brown/blue feed splits into two and also feeds the light switch which is still unfused and the side lights can turn on when ignition is off. A DHC with roof down is vulnerable to malicious tinkering and battery drain.
3. The White cable from the ignition switch to the fuse box is unfused.
4. The white/purple cable from the ignition switch to the fuse box is unfused
5. The brown wire from the ignition to the windows is unfused and will work with the ignition off.
6. The white/black cable from the ignition switch to the coil is unfused.
7. The white/red cable from the ignition switch to the started solenoid is unfused.
8. When the car is running, lights are on, wipers and heater on, the brown/blue cable and ignition switch are carrying the total amp draw, unfused. Feed to coil is unfused. Also the two feed wires to the fuse box are carrying load unfused.

With how the dash and engine wiring harnesses joins behind the glove box, I'm clear that I can add extra fuses to protect the different downstream circuits relatively easily here. I can see lots of suggested approaches on threads.

My question is what have people done to protect the brown/blue feed wire and ignition switch and the unfused feeds from the ignition switch to the two fuses in the fuse box?

1. One big fuse and hope that the ignition switch can cope?
2. Add relays so that the brown/blue wire acts as a 'control' wire and not carry full load?
3. Separate (fuse and cable) for brown/blue feed to ignition and brown/blue feed to the lights?
4. Fuse to brown/blue feed to control box and separate fuses near the back of the ignition switch to protect the feed wires?
5. Nothing and hope it doesn't fry and burn the car?
6. Something else?

I would welcome your thoughts and experiences.
The car body is on its new chassis and painted but nothing has gone back in yet, so now is a good time to do modifications.
I have new harnesses from Autosparks, but they mirror the original design - faults and all.

thanks in advance
Jem

[ericbushby]

Hi Jem,
I do agree that more fuses are needed but as I have never rewired a car I cannot advise you from experience.
One point though, If a switch is rated at 15 Amps, that will be it`s continuous rating. It will be quite capable of carrying several times that current for the short time it takes a fuse to blow.
Others will be along soon with more practical information.
Eric in Burnley
1967 S3SE DHC

[HCA]

You are correctly describing mst British cars of that era! Most survived a full life with unfused circuits. When you look at the detail from a manufacturing point of view, the circuits that are unfused have a low risk of shorting against the cost [then] of a fuse box. eg outside of a smash or the loom being disturbed/broken, the light circuits should not catch fire, nor your white/red etc.

In defence of the car industry, I do not think you can accuse them of installing faulty wiring - economically deigned, yes, but not faulty. I have owned many cars of this era, and must say that the only times I had trouble was self made (twisting joints and not using insulation etc..). The only time I can honestly say a fire was not of my making was a Mini Cooper S where the main cable leaving the battery chafed on the body on the grommet drying out.

But yes, you are right, there should be more fuses. Relays not so important as the loom was made of heavy cable and they build switches to last.

By all means, fuse whatever you want. How you do it on an existing loom is down to you. Or rewire the car completely yourself. I have rewired mine using thinwall so that each device has a dedicated circuit and returns back to the battery rather than using the chassis. I use a fuse box with 50 fuses that is more than enough. Using LEDs everywhere, relays are not necessary outside a few heavy draw items - front and rear screens, wipers, air horn compressor, and front fans.

[RichardHawkins]

Jem,

I did as HCA. I think the crucial difference between our cars and other 1960’s cars is our glass fibre bodywork which cannot be used for the earth return. Lotus did what they thought was adequate at the time, and did not imagine we would be cherishing and restoring their cars in 2022.

A word of warning, I have never re-wired a car before and have made many mistakes, the work has taken approximately 2 years.

Hope this helps,

Richard Hawkins

[HCA]

You are taking this into another realm Richard - that of earthing!

Car wiring is only the means to connect all the electrical devices to a battery and quite straight forward and only complicated by the quest to do it economically.

The many GRP bodied cars of the time used the chassis for the earth return. GRP monocoques such as Ashleys and boats could not do this and cabled back to a central earth at the battery.

99.99% of wiring problems are in the earth. Using a negative earth causes a car body or chassis to become a sacrificial anode at the points where earth wires terminate. Connections might appear to be tight, and they are - but corroded and become poor conductors. Many do not appreciate this and rip out good wiring thinking it to be the problem. So it is not british car wiring or GRP bodies at fault, just a misunderstanding of the humble earth.

To do the job properly, return everything to the battery, or at least tin all earthing points.

[Jem]

thanks,
my concern isn't about components failing due to poor earth. I was planning to add additional cables as earth routes so not to rely on the chassis.

I'm comfortable with wiring and modifying the harnesses.

My main concern is the protection of the live side of the main feed cables through the ignition switch.

[stugilmour]

Jem. Coles Notes version is I used a variant of your ‘one big fuse and hope for the best’ layout. Here is some more elaboration…

I left the main Brown from the alternator to a major positive pole under the hood unfused. This main Brown is fully sheathed and solidly attached to the firewall in the engine bay.

The main positive pole I installed replaces the remote starter solenoid in the stock setup; I use a modern starter that does not require the remote solenoid. This pole also connects to the main starter cable and main positive battery cable. This results in the removal of the stock voltage regulator and the dash ammeter in the Plus 2 (functionally replaced with a voltmeter). The pole bolt can be reliably used to charge or jump the car or check battery voltage without fussing with the battery in the trunk (very inconvenient in the Plus 2 as below the floor boards).

This main positive pole basically represents the start of the loom. Perhaps this is more apparent in my car because it is based on a modern aftermarket loom supplied by Spyder and the generator/ regulator was never present. All the fuses and relays were intended to be glove box mounted, although the cooling fan relay ended up under the hood near the temperature controller and is fuse protected at the box. I have kind of lost track of how this setup relates to the various Lotus layouts, but to me this reflects modern practice.

The loom downstream of the main positive pole (basically every other wire in the car) is protected with a fusible link. I think mine is 50 amps. They come in their own isolated capped plastic mount, and are a very large slow blow fuse. It is mounted under the hood before the firewall grommet, and is carefully protected with heat shrink and liquid electrical tape. That hopefully takes care of any direct shorts. Come to think of it, I can’t recall where the heck my spare fusible links are, but a few spares should always be readily available; i.e. dead in the water if it blows. Basically more likely to blow when fiddling with the wiring rather than in use I suppose.

One improvement I just thought of. Consider isolating this main Brown to a single conductor connector, or pair it with the White/Red starter solenoid trigger and make the connector accessible under the dash right side. Both are pretty hefty gauge wires. This strategy would allow a small amp fuse to be easily inserted for trouble shooting, thus preventing blowing the fusible link. Come to think of it, I think I did it this way. In any case, a connector is required to allow dash removal, so not really an adder.

Another thought. My LHD car puts all of this stuff on the right hand side. Obviously modify as required for RHD.

The Brown and White within the loom are still considered Unfused, and are not interrupted with any other fuses. If needed I could look up what uses Brown and White connections, but it is pretty limited. It does include the ignition and starter systems. This means that the Brown/Yellow back to the alternator through the dash ignition light, the White/Red to the starter solenoid, the White to the voltmeter, and the White/? to the coil & electronic ignition remain technically ‘unfused’, but they are protected from a straight short by the fusible link. I think that is about it for the commonly ‘unfused’ stuff.

I think my 10v voltage stabilizer for the gauges is also supplied from the White bus, but that could be just as easily supplied from Green; just convenient as the stabilizer is right next to the ignition key and it wasn’t worth changing in my loom. Similarly there is a short unfused wire to the inline accessory fuse (forgetting the exact reserved colour right now). Afterward I installed an accessory bus to the single inline fuse, which takes care of separate runs for all the modern annoyances like radio, Garmin, USB charging, etc.

Thinking about the layout now, perhaps all of the unfused runs between the ignition key and the main fuse/relay box could be easily grouped together and inserted in continuous sheathing to completely protect them as they wind through all the dashboard attachments. In the Plus 2 there would only be the takeoff leg to the voltmeter to take care of in the run. I have seen some of the diagrams that wire ignition through a green, but I don’t like that in case of some intermittent failure at the fuse. In any case the unfused ignition wires would only extend from the main box through the firewall.

In terms of the fuse box circuits, I think I have about 16, which upon reflection seems about right. There are two Green and two Purple to take care of most of the car. The six low, main, and driving lamp filaments are all individually fused. The accessories, fuel pump, and cooling fan are good to be individually fused. My Plus 2 window lifts have four fuses, but really could have been done with two (which is how it will work for the Elan). At any rate, for sure fuse the lift motors separately as they can easily blow at stall; bad enough loosing a window but a real pain if it effects other functions. My heater fan is separately fused, which is probably unnecessary; at a guess the universal loom may have been designed this way to cleanly accommodate kit cars with no heater. The in-line style accessory fuse is remotely mounted close to the ignition switch simply for convenience, but I would try to integrate it into the central fusebox if doing things again. The left & right side lights are the last two fuses; I suspect the loom kept them separate so they could be switched separately as onside or offside parking lights but I think both sides could just use a single fuse.

In terms of relays I am having a bit of difficulty remembering detailed count, but think in terms of 12 to 20. Basically 4 for the Plus 2 window lifts (different for the Elan), 2 for sidelights, 2 for the heater fan, 3 for dip, main and driving lamps, 3 for the hazard & indicator flashing supply (peculiar to my loom), horn, cooling fan. In addition I have subsequently remotely added a control relay for the light pod motors (two may be required in some setups), an isolation relay for the brake switch to accommodate cruise control, a relay for the audio amp (needs to be in the trunk for sure), and two relays for seat heaters (they came in a fully prepped loom so will end up remote anyway). Might have been nice to have included some of these in the initial design I guess, but I ran out of slots and couldn’t even fit a fuel pump relay. If doing again I would probably ditch the heater fan relays and add an integrated fuel pump relay.

My loom also has one remotely mounted flasher, the Lotus practice is two (hazard & indicator). Would be nice to have them in the main relay boxes if three pin bases are available to fit? Not sure, but maybe a five pin relay base can stand in for a three pin flasher base? Top tip: install LED compatible relays now. At a minimum document where the heck they are installed and make sure they are accessible without removing the dash!

I have added some stuff to the car over the years, so having some spare Green and Purple is probably smart. I would definitely make sure I have Green and Purple runs to under the hood, available under the dash, and into the trunk. Very handy.

One thing I wish I had done differently. Make sure any individual function is protected by the minimum number of fuses. e.g. I think my electric light pods somehow ended up connected to both Purples. Similar thing happened with my hazard setup. This is easy to do when using relays; as best you can keep the relay trigger and power supply consistent or at least document how you did it. I think it would be better to make sure all the added relay triggers came from the same two Purple and Green fuses; my setup is a bit random on that deal.

Sounds like you have a plan on the ground side. My loom included numerous ground runs, which is the way to go. I installed a central ground bus at the right side dash bolt. There has developed a second ground bus in the trunk, mainly due to audio stuff, but to stay consistent it is still grounded back to the main ground at the dash bolt. The main battery ground cable is moved to the right side tower body bolt. Both of these ground bolts thread directly into the frame, which works reliably as a ground with only one cable connection under the bolt head.

Taking another look at your specific questions.

Yes, there has to be Brown and White unfused runs from the ignition switch to the fuse box. Pretty much unavoidable. Even if you installed a main relay for all of the White functions you would probably want the trigger wire from the ignition key to be unfused. These runs rely on the fusible link for protection.

The various supply wires you mention will all now be internal to the fuse / relay mounting box(es) so not really an issue. Not sure of details on White/Purple, but it lists as fuel pump supply? Presumably some of them are vestiges of different supply points on the stock regulator (voltage or current regulated IIRC) but it has been a long time for me on that deal. Sounds like your loom has in effect a Brown and a White common bus at the ignition switch, which sounds inherently more problematic than a single Brown and White run from the main fuse / relay box(es) to the ignition key.

To prevent someone turning stuff on while the top is down, easiest to simply move the associated relay trigger supply (through the dash switch) to the Green fuse rather than purple. Some modern cars do use an Unloader Relay to turn off a bunch of stuff while cranking the starter, but I decided that was a bridge too far.

I have not looked at the various Lotus diagrams in a while. Just describing how and why I did mine. There are probably obviously easy ways to modify the supplied loom that are a bit different than how mine is set up. Any ideas around those details are probably of interest to others doing the job starting from one of the new looms.

Quick remark on documentation. Rather than go crazy modifying a Lotus schematic drawing, perhaps what I did will help. The aftermarket loom documentation was pretty scant, more of a connection list. As I had to do my own drawings anyway, I tried following conventional BMW practice. They publish an ETM or Electrical Troubleshooting Manual for each car. Separate pages for each major circuit grouping, fuse layout, relays, power supply, charging, etc. Even have pages for connector drawings and location photos. Google up an ‘80’s version of an ETM (any model) and use that as a go-by. Very well done. A bit extreme for custom wiring maybe, but still an excellent breakdown of how to organize yourself. I used about a dozen 11 x 17 cardstock sheets to draw things out and make notes. The idea was to photocopy to a smaller size to carry in the car, but never ended up doing that as they can easily be scanned into your phone or iPad for mobile use.

I have had my car’s wiring modified long enough that I am now my own DPO (Dreaded Previous Owner). Although the general documentation approach I took is the way to go, I could have done a way better job documenting the location of things and connector pin details. Turns out this is the detailed information you need five years later when troubleshooting or modifying/adding stuff, and of course no one can help you. The reality is failures and changes mostly occur at the connectors. Although I recently had to trace down a wire failure that occurred at the firewall grommet, it is the connector pin details you really need to straighten things out.

Last top tip. To prevent multi pin connectors becoming disconnected, wrap a zip tie thru the wire bundles and cinch the connector blocks together. I had issues when I was fiddling around doing troubleshooting where gaining access to a connector would accidentally pull another one apart. I try to use one colour for all these temporary zip ties, and just snip and replace if I have to work on an individual connector.

HTH Just my setup and thoughts. Had never done anything like this project, so completely open to feedback. Sorry for length; had just started an offline conversation on configuring a new Plus 2 loom so trying to answer a bit on that topic at the same time. Let us know how you end up doing your car.

Stu

[Jem]

thanks Stu,
in my setup it makes sense to add a big link fuse onto the brown cable coming out of the starter solenoid. I have a high torque starter so technically don't need the solenoid. I might remove and use a positive pole as you have or keep if in the engine bay for 'look' but wire the starter and starter solenoid to connect to the same side of the stock solenoid and effectively bypass it.

the link fuse will protect the brown feed to the control box and then split brown/blue feed to the ignition and lights into two fused circuits.
the blue feed to the lights can then be fused and the green/purple circuits and also split by function.

on the documentation, I have used Adobe Illustrator to draw the standard individual functions as the full wiring diagram is hard to use. This is working well and is pretty easy once I worked out how to draw with a multi-coloured pen.
You can see a bit of a sample in the image.

I'll draw in all my mods (like electric fan. fuel pump, radio, fuses etc) so I have a proper record and I'll know what I've decided when I'm actually working in the car..

I'll come back with what I decide to do so we can compare.

thanks again
Jem

[stugilmour]

Looking great Jem.

Two quick points.

I added a two pin connector into the White / Red wire under the bonnet. I can plug in a starter switch so I can turn the car over while fiddling with timing and carbs. Handy if you remove or wire around the firewall mounted solenoid.

For the loom details from the regulator area to the new fuse/relay box, it kind of depends on where you decide to mount the new fuses & relays. If mounting in the glove box area so that they are all attached to the dash and can be removed as a unit only one Brown is required thru the firewall and the loom can be largely revised with the dash out of the car and the various runs stretched out on the floor. If some or all of the new fuses & relays are remaining or being added to under the hood, the firewall grommet area becomes potentially more complicated with relay trigger wires extending off of the dash unit.

I went with the glove box attachment option based on great posts from Grumpy Bodger. He posted some very nice pictures of his modified Elan wiring.

Although in stock form later versions of the Plus 2 had additional fuses and relays under the hood, I found my LHD Federal car with two brake boosters was way too crowded to do it that way. Also wanted most of the wiring on the interior.

I used the standard wire colours (in smaller wire gauge) for the relay triggers. The larger wires of the same colours run from the relay to the loads. With the fuse/relay box(es) all on the dash this is easy to keep straight. Figured not so easy if wires were going through the firewall.

All the best. Great idea on the software for the diagrams. I was trying something similar in PowerPoint, but found it easier to sketch.

[Jem]

Looking great Jem.

Two quick points.

I added a two pin connector into the White / Red wire under the bonnet. I can plug in a starter switch so I can turn the car over while fiddling with timing and carbs. Handy if you remove or wire around the firewall mounted solenoid.

For the loom details from the regulator area to the new fuse/relay box, it kind of depends on where you decide to mount the new fuses & relays. If mounting in the glove box area so that they are all attached to the dash and can be removed as a unit only one Brown is required thru the firewall and the loom can be largely revised with the dash out of the car and the various runs stretched out on the floor. If some or all of the new fuses & relays are remaining or being added to under the hood, the firewall grommet area becomes potentially more complicated with relay trigger wires extending off of the dash unit.

I went with the glove box attachment option based on great posts from Grumpy Bodger. He posted some very nice pictures of his modified Elan wiring.

Although in stock form later versions of the Plus 2 had additional fuses and relays under the hood, I found my LHD Federal car with two brake boosters was way too crowded to do it that way. Also wanted most of the wiring on the interior.

I used the standard wire colours (in smaller wire gauge) for the relay triggers. The larger wires of the same colours run from the relay to the loads. With the fuse/relay box(es) all on the dash this is easy to keep straight. Figured not so easy if wires were going through the firewall.

All the best. Great idea on the software for the diagrams. I was trying something similar in PowerPoint, but found it easier to sketch.

do you have a link to the posts - my searching skill seem flawed as I can't find them

[stugilmour]

These threads have couple of pictures of his flush mounted fuse box (and I think some relay bases). The second thread shows the dash from the rear

viewtopic.php?t=17787&p=95881

viewtopic.php?t=29880&p=198792

Here is a thread with a more compete overall description of his lovely Elan

viewtopic.php?f=19&t=19087

This is the brief description of the wiring…



The glove box was fabricated in aluminium in order to accommodate a comprehensive range of electrical relays & a multiple fuses; it is lined with leather.
The wiring harness is completely new utilising modern connectors & complies with modern automobile electrical standards.
Separate harnesses are provided for the, engine bay & the rear of the vehicle.
Multi-pin connectors, connect these to the dashboard harness. The vacuum operated headlamp mechanism (fitted with new vacuum units) is electrically actuated. A new 80 Ah alternator & new Ford pre-engage starter motor are fitted.