Lotus Elan

help with wire thickness/amps

PostPost by: rgh0 » Wed Jun 08, 2016 1:36 pm

You may have noticed in my Elan the small aluminum panel below the dash at the right that holds a battery cut out, a manual electric fan switch and a hazard light switch-- all useful additions in the modern world and / or when racing

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PostPost by: prezoom » Wed Jun 08, 2016 3:49 pm

I think I posted this reference some time ago, but in figuring wire size and loads, I have found these charts to be very helpful. Try rbeelectronics.com click on misc then wire tables.
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PostPost by: dgym » Wed Jun 08, 2016 9:44 pm

Thanks Rob!
1967 S3 Coupe (left the factory in 66)
original rego PPC 8E
original owner B.M. Wetherill ..are you out there?
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PostPost by: bob_rich » Thu Jun 09, 2016 10:27 am

Hi dgym

I think you have got enough info to make a good job of the new loom. Despite the likely cost being a bit more I think that a use of modern fuses ( and more of them !) and connectors with modern wires will give a much better job. On the originally question my view is that any Elan is likely to be + 40 years old and the original wiring is bound to be in a pretty poor state and well worth a change and will be a small fraction of the money spent on a rebuild.

A couple of final ideas that may help.

(1) To cut down the number of wire type you could use strands in parallel this means you can buy less wire types and increase the quantity perhaps saving a few pennies. I did this on my window motors because I found that they did vary quite a bit in current demand. Also by doing this I was able to match the colour code of the wires more readily as thinner wires came in more colour options that the heavier current wires.

(2) I would put a fuse in series with the main alternator (generator) feed 10A more rating than the alternator (generator) would seem suitable. In effect the battery is connected directly to the generator and a failure in the regulator or rectifier means the battery can dump high current into the alternator (generator) circuit and this wire can burn out very quickly if this fault, albeit a remote one, did occur.

(3) Modern blade fuses have well defined interrupting characteristics and it should be easy to pick a fuse that will protect the wire, permit starting surges of motors and bulbs, and be quite reliable in operation. I have attached the data sheet for a typical fuses found in auto applications. There rating allied to the interrupting capability make useful reading.

So go for your own loom you won't regret it !

Best of Luck

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PostPost by: gus » Thu Jun 09, 2016 2:42 pm

18 ga wire will handle most standard loads
14 ga for the windows
for the main feed to the fusebox, get the big lucas wire, plain brown 84 strand, as it is softer than any other standard wire you can find

See what pricing you can get on ETFE insulated wire. Cheaper than teflon and just as high a temp rating

I just cannot see putting pvc wire in everything...........

One can buy pretty standard connectors cheaply and buy gold plated crimp contacts for the areas in the nose where the weather gets to them
http://www.newark.com/te-connectivity-a ... gQod3_sJiw

available 2,4,6,10 position.....

for the standard quick disconnect buy the best you can, nothing from a retail outlet is worth using. Nylon insulated rather then vinyl are usually higher quality

the 'proper' way to build a harness requires two things.

A run list and a harness board

The run list is hard. It is a list of every single wire from where it starts to where it ends. A separate entry for every intermediate connection, so if you are making an organized set of connectors at the firewall instead of a useless pile of bullet connectors, that becomes a set of connectors, for instance J1/P1 is a connector pair, J or "jack" is one side, P or 'plug' is the other

the attached PDF is my run list from 20 years ago when I did my +2, IIRC J1,2,3 are the firewall connectors.

The harness board is easy. your dash pretty much needs to be out to do a harness, trace it on a piece of plywood and drive a nail in every spot for a switch or gauge and label it. Measure where things go off the dash and figure where you are going to need a bend and draw it on the board. Do a separate one for the engine bay, it pretty simple, drive nails for the SOVY, alternator, fan, headlights. Only one cable goes to the boot, you could wire that in place pretty neatly

To build your harness you print out a copy of your run list, and when you run the wire, you cross it out with high lighter. Remember to leave a service loop on the ends of things so you can get the gauges out of the dash for instance

then you need to crimp the pins on the ends of the wires, and put them in connector housings if you choose to do it that way.

Then you ring every single wire with a meter and cross that line out on the run list in red marker.

Then you take it off the harness board, plug it in and have it work the first time........

other notes. Buy a little bag of 'ring tongues' for all of the gauges so you can use 1/4 quick disconnects for everything.
nothing wrong with glass fuses, still can buy them everywhere around here.
Little is wrong with the Lucas harness other than total crap materials, some undersize wires, and not enough grounds. I fused both windows separately and otherwise left it mostly as is, one switched fuse, one unswitched, no new relays other than the fan. 14 gauge wire to the windows and grounding them will make them seem possessed,

The only error in the PDF AFAIK is the high beam circuit is not quite right, having to do with the added solenoid, and the fact that they wired the microswitches stupid from the factory. The High beam light will switch on and off even when the lights are not on, and maybe I added a diode in there......

Anyway, quite simple really..............
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PostPost by: stugilmour » Thu Jun 09, 2016 5:03 pm

A couple of options for you, as you mention you are not fussed with originality.

When I did my Plus 2, I used a Premier Wiring Lucas Uniloom as the starting point. I purchased mine from Spyder Engineering about seven or so years ago. They apparently used them for their Zetec conversion rewiring jobs. Not sure if they still use them (or something similar), but might be worth a shot. They were mentioned in a recent thread as offering complete rewiring services.

Here is a link to the Uniloom manufacturer's web site. I have not been in touch with them, but might be worth a try. I bought mine before the mentioned move to Spain, so unsure if they still trade; if you do opt to try contacting them let us know. Most Google references to them are pretty dated though, so thinking Spyder might be worth emailing to see what they have.


I have posted info on the Premier Wiring Lucas Uniloom before, so a search here might bring up some additional detailed info.

This is a universal style loom that is/was popular with the kit car and LoCost crowd. The main advantages for the Elan are it already has numerous centralized ground wires in the correct cable sizes within each leg of the loom. It also uses the British Standard BS-AU7 wire colours, which is largely similar to stock Lotus practice (e.g. Lotus departed from the standard with the wiper circuit). Because the dash portion of the loom comes wrapped with simple twist ties it is very easy to modify for relays and additional circuits (e.g. window lifts, emergency flasher switch, single dash pilot for turn signals come to mind), or move things around to suit the Lotus dash layout, either LHD or RHD. For example, if you use the stock Elan temperature gauge you could easily remove the included sender wire from the loom, and I think I had to add wires for brake fail, door and dash interior lights, and low fuel warning in my Plus 2. The loom is already set up for an alternator, so no confusing vestigial regulator wiring. All wires were correctly sized and generally of appropriate length. I can check if you want, but I think it has two Green (Hot in Run & Start) and one Purple (Always Hot) fuses. Any supplied connectors are of modern blade design, not one bullet used. :D The turn signal & emergency flasher circuits are rationalized to modern practice with one readily available flasher relay rather than two.

The loom design and layout are completely coherent, and it was supplied with pretty good connection instructions rather than a difficult to read schematic. A blade type fuse holder (eight or ten fuses, I can look if you need) is included within the loom, and the circuits are well balanced. I modified mine extensively to add relays to all large loads, three relays to allow use of the emergency flasher stock dash switch, motorized headlamp lifts, window lifts, etc. With the correct "double roll" crimper and connector block tools it was easy to move things around or upsize wires, etc. I think the various loom legs came with flexible black plastic covering (not the cheesy looking split stuff, but a full black tubing type deal); at any rate I added these a required by fishing the wires.

I mounted the relay and fuse boxes to the back wall of the glove box so everything stays nice and dry while remaining easy to access. I changed out the supplied fuse box to a design that also accommodates various sized relays, which was easy to do with the correct connector tools.

This is by no means a simple drop in wiring solution, but would save you all of the design issues and includes all the required large gauge Brown, White, and Black wires. It makes an excellent starting point, and I was able to understand it easily. I purchased modern connectors from Vehicle Wiring Products and AES. The loom comes without connectors installed so that all the run lengths can be modified to suit your application. After fitting the loom in the car I cut the main legs at the dash to add modern multi connectors, which makes dash removal way easier. I completed the whole project on my own over the winter months with no previous auto wiring experience. I removed the dash and all existing wiring, and laid the whole issue out in the warm basement, so wiring and testing was easy.

Anyway, highly recommended and saved me a ton of confusion on basic loom design.

The other route to consider is something like the Painless Performance loom. These are typically North American sourced looms popular with the Hot Rod community. I don't recommend these because the wire colours don't reference the British standard. The advantage is they come with relays for some of the large loads. Perhaps there are some wiring diagrams on line that would help you out if you opt to design your own loom.


Anyway, best of luck with the project. It is well worth it, and can be done with patience. The most significant benefit of doing the rewire myself is I now fully understand every wire in the car. Since installing and correcting the inevitable initial errors the car has been completely trouble free electrically.


Last edited by stugilmour on Thu Jun 09, 2016 11:22 pm, edited 6 times in total.
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PostPost by: gus » Thu Jun 09, 2016 6:05 pm

I don't think the generic/hotrod looms are a great idea, but I will say the painless looms write the wire function right on the wire, how cool is that? 'left blinker' or 'heater fan'

pretty cool
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