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
Posted: Sat Jan 15, 2022 11:28 am
