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MG TD TF 1500 - Home Made wiring loom.

Me again! I can't find anything using the search function.
I'm quite keen on making up a new wiring loom for the TD mainly to save money. A Moss loom is, from memory, about 245 the raw materials would be under 50! save me time as well, has anybody got a plan to work from in terms of dimensions and details of the "splits".
Wiring diagrams and wire colour info is all over the Web but I cant find a "how to" guide for this car. I obviously can't do the braiding, it will have to be cloth covered tape I suppose but that doesn't bother me at all.
Its a LHD.
c caygill

I made my own. My problems were that I didn't want to recreate the flaws that made the TD wiring so unreliable, and I wanted to include relays and other appropriate modifications so I'd have a TD with electrics that actually worked and kept working. Cost was less of a consideration, but my total costs were somewhat lower than buying a harness.

I could not find appropriately striped wiring for a sensible price, and even if I could, it probably would be limited in selection. By dispensing with that requirement, I could select wire that was the right size and had high-quality insulation. Remember that a lot of wire available these days is NOT copper; it's copper-plated steel. Worse, the insulation is flammable and has a low melting point. This is prescription for a fire in any automotive application. The downside is that, in one or two places, the user will have to tag wires if they are disconnected. Not a big deal.

The real question, then, is what you want to accomplish. I wanted a car that worked, and that preserved the appearance of a TD, even if not precisely original. This may not be what you want; I don't know. If you really need something that is original looking, because you want a competitive show car, you probably should just buy a harness; it's probably small change compared to what other things will cost.

Anyway, here's the story of my wiring job:

S Maas

Colin, I'd suggest that you investigate the cost of buying small amounts of many color-coded wires before you jump into this. Minimum-purchase issues can raise their ugly heads.
Many years ago I fed my family as an electronics technician while I was working on my engineering degree. Creating wiring harnesses was standard procedure. We would take a full-sized drawing of the instrument and attache it to suitable piece of wood. A nail was driven into the board at every spot at which there was a wiring point. We'd wrap the end of an appropriately colored piece of wire around a nail and weave it through the bed of nails until it got to its connecting point. This went on ad-nauseum. Once all of the wires were in place we would take a spool of harness lacing chord and start lacing. It was quite a few years before the calluses disappeared. Good luck. Bud
Bud Krueger

Hi Colin,

I made up a loom for my TF and it was one of the most pleasant jobs of the rebuild. In fact a friend of mine is currently making a loom for his TD. I simply laid out all the wires on the car itself and temporarily taped them before finally removing the whole lot and covering in Tessa tape (superb stuff!). I made many improvements such as relays and fuses. I had to remove the temporary tape a number of times to reroute or put in extra wires. The big advantage of fitting the loom to the car is the ability to put branches in the exact places needed. I cannot recommend too strongly that you get a copy of the Vehicle Wiring Products catalogue. This will give all the info needed to calculate wire sizes and they can supply everything you need including all the correctly coloured wires. BUT you do need a good knowledge of electric circuitry and a set of instructions isn't really appropriate.


Jan T
J Targosz

Sounds like a fun job, as Jan says. Very satisfying to do it exactly the way you want!
Geoffrey M Baker

I am the friend that Jan refers to in this thread, and can endorse his comments.
On his advice I bought the wiring ( in the correct colours ) from Vehicle wiring products,downloaded the wiring diagram , and simply built up the loom a bit at a time.
If you do this, (lights, then indicators etc) you can test each function as you go along and correct any errors.
I also added extra earth wiring to the lights,instead of relying on the body panels to act as earth.
As Jan says ,it is a very pleasant and rewarding job, and the Tessa tape gives a professional finish.
IW Martin

Thanks to all who replied. Much appreciated. I will carry on with the job as suggested. Well, as soon as I get the body tub finished!
c caygill

Colin - and anyone else doing this or who has done it - it would be enormously handy to have a shopping list of wire length and color. Then any of us, when we get around to this job, could use that as a basis for our (probably modified) wiring loom. Vehicle wiring products supplies a staggering number of different colors, thicknesses etc.
So please, if someone undertaking this could keep their invoices and measurements...?
Geoffrey M Baker

Good idea Geoffrey. I have found this which might be helpful at least to UK owners.

I'll post any other info I come across although its going to be in the new year before I can start on the wiring...too much other work to do.
c caygill

Just had a look and they ship worldwide!!
c caygill

I've got a local store which will sell wire by the foot and has a wide array of colors etc. But lots of online places have everything you need... Ron Francis wiring in the US and Vehicle Wiring products in the UK are just two...
Geoffrey M Baker

Hi Colin, and Geoffrey,
I made my own loom for my RHD TD. And since the main time consuming job -but interesting- was to draw the manufacturing schematics that don't exist anywhere. I wrote an article in TTT2.
You will find everything needed to build the loom. Wire colours of course but also gauges, length, conduits, terminals...
Easy to adapt for your specific car.



LC Laurent31

Thats what we're looking for Laurent!
Many thanks.
c caygill

Awesome, Laurent. Thanks so much!
Geoffrey M Baker

For anyone thinking about doing a complete rewire, who is also considering extra fuses, relays for horn, brakes and headlamps etc, you might want to think about the ultimate electrical accessory:'s "M-unit". This is a box the size of a cigarette pack that contains ALL centralized electrical switching and protection for a vehicle.
That means: Headlamps, running lights, brake lights, turn signals, horn, accessories, starter... everything.
Digital processing offers full voltage protection on ALL circuits (no relays or fuses needed whatsoever), even protection from reverse polarity.
So in other words, it gets rid of the fuses, flasher, control box, and all relays. It also offers a thin-wiring solution to all control switches, which need far less amperage to run.
Additionally, it offers:

A built in alarm system.
Self cancelling turn signals
Modulatable turn signals

It's designed for motorcycles, but I see no reason it could not work with our old cars. It supplies 30A to the starter, 16A to AUX, and 10A to all other circuits.

In conjunction with two other products from motogadget, it can also offer an ignition safety lock, and, interestingly, a 'm-button' device can be used to simplify wiring, requiring only one wire to connect to the dash panel to control horn, lights, and turn signals.

Only for those who absolutely don't care about originality, but for people looking to improve (and simplify) their electrical systems, this is a very cool device!

I had one on my motorcycle and loved it. Sadly, sold the bike with the unit.
Geoffrey M Baker

Absolutely brilliant, but if it goes wrong you are completely b******d.
Dave H
Dave Hill

Dave, you could always carry a spare in the glovebox :)
Additionally, it's circuit protection shuts down any circuit and lets you know which one is causing the problem, allowing for much easier troubleshooting!

I had one on the bike for years and never had a problem, the thing is waterproof and foolproof.

Geoffrey M Baker

That 30 amps for the starter better be going to an added relay for the starter. It would appear to require a total rewiring of the Tcar's simple, direct, electrical system. Think I'd rather KISS. Bud
Bud Krueger

My post was predicated on the fact that someone would already be rewiring the vehicle from scratch, Bud.
Geoffrey M Baker

I recently rewired my TC. I was a bit bothered to find that virtually nobody sold the correct type of copper wire. The usual suspects sold the pvc and the fancy braided kind of insulation, but the wires inside were wrong. I suspect the TD and maybe TF also came with pre-tinned copper wire. Not just tinned at the ends where the connection is made, after you brush or sand off the copper oxide coating, but tinned the entire length of each strand of the multi strand wires. Generally nowadays it is called boating or marine wire and can only be found in pvc or sometimes silicone insulation. The silicone insulation is quite expensive. Here's one source of pre-tinned wire, look under "primary wire":
and another that may or may not be of better quality?
search "tinned marine wire"

Pre tinned copper wire makes for much less work when creating bullet or other soldered connections. It is not noticeably stiffer than non-tinned copper strand wire.
D mckellar

This thread was discussed between 28/11/2015 and 02/12/2015

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