Category Archives: Rewire

Rewire – in colour!

One of the best loved features of the M-series TVR’s is that the wiring is done throughout in black wire with coloured rubber sleeves at each end to identify the circuit. Over time, the colour of these sleeves evolves to a beautiful dark brown, making circuit tracing impossible. I first encountered this quirk whilst trying to fix the headlights which had failed around the car’s 2nd birthday. This turned out to be due to corroded connectors exposed to all the muck and bullets of the front wheel arch down near the offside bonnet hinge.  Many years later, the grease that I had smeared the new connectors with to protect them was still in place and preserving the contacts! However, one of the early decisions regarding the wiring was that these bullet connectors would be replaced with waterproof connectors.

original bonnet wiring

Back to the rubber sleeve issue, I found out all those years ago that by rolling them inside out the colour could be identified since the inside of the sleeve hadn’t faded as much as the outside. My mistake was to not turn the sleeves back again – so that over the intervening time both inside and outside became the same shade of deep chocolate brown thus ensuring that many hours were required to decode the loom so that I could make a new one.

This article therefore covers the ups and downs and the fun I had in getting the car re-wired, which happened over a long period of time and overlaps with some of the previous articles. At this point I should declare that I understand much more about electrics than the mechanics of the car. However, I was still hoping at the outset to be able to buy a replacement loom and just connect this to all the new electrical items but once I had stripped out all the wiring and saw the issues with the original concept, I thought there was no alternative but to design and build new wiring looms myself. Probably the correct decision but more time consuming than I originally thought.

As I was stripping out the loom it became obvious that none of it was going to be re-used. The picture below shows what I discovered when I removed the dash (probably around 3 years ago now). The connectors had pulled off the fusebox terminals and the rest was a real rat’s nest and a daunting prospect to try and unravel and trace, let alone rebuild. Despite that, I was determined to label everything that I could identify to help in tracking down what was connected to what, where and how.

original fusebox wiring

The dash wiring wasn’t in too bad a condition but I could see that some of the terminals needed replacing and the instrument earths needed new life so again decided it all had to be replaced.

original dash wiring

Similarly, the boot wiring was basically OK so the main motivation in replacing it was to have the wires in the correct colours and to get new terminals and connectors on everything to improve reliability. The bonnet and engine bay looms and connectors had suffered as shown in the first picture above so there was no alternative than to start there from scratch as well.

The main part of the wiring loom (engine bay and behind the dash) was labelled and hung on the garage wall. Bit by bit this was dissected so that I could trace out the individual circuits and see how they connected to each other. I had the original circuit diagram from the car’s handbook but this contained a lot of extras that the 3000S didn’t have (e.g. heated rear screen switch) as well as a few obvious mistakes (such as the brake warning circuit is shown earthed at both ends with no supply voltage) which didn’t build confidence in using it as a guide for a new loom. On top of this, a circuit diagram doesn’t show where all the real connections are made so, in terms of working out what connectors to order and what the lengths of each wire colour should be, it was no help at all.

main front wiring loom

I therefore set about drawing up the circuits in CAD (TinyCAD to be exact – free and easy to use) starting with the Battery, Starter, Ignition and fuse circuits. The circuit below is probably tricky to read at this size but clicking on it will bring it up in full screen resolution that should then be easy enough to read. I suppose putting up circuit diagrams on a car blog is like putting equations into popular physics books (à la Stephen Hawking and “A Brief History of Time” where only e=mc² featured). So this will be the only one – promise.  If you’re interested in the full set just let me know and I can email them to you.

GLB746T fuse circuits 5

The main idea behind starting here was that I wanted to replace the original Lucas 4 way glass fuse box with the more reliable blade fuse system. At the same time I could fuse individual circuits, hopefully making the electrics safer as well as more reliable. I finally decided on the arrangement shown using two 8-way fuse boxes, one for the unswitched circuits and one for switched. This still doesn’t fuse every single circuit but with some logical doubling up on the supplied circuits, it’s a major improvement on the original system of 4 glass fuses (IMHO).

The next thought was where to locate the new fuse boxes. There would have been space where the original box was located on the bulkhead and it would have been easy to access the fuses from the engine bay but would also have been an obvious modification. Since one of the goals of the restoration was to change as little as possible I decided to make it not so obvious and locate them in the driver’s footwell. I blocked up the hole with P40 and a couple of layers of matting on the inside and in the engine bay it was covered by the heatshield . That way, I don’t have any leaks through the bulkhead and the absence of the old 1970’s box will not be so obvious as the presence of 1990’s new technology.

This picture shows it as work in progress as a hingeable flap containing fuseboxes and the relays for the Dip and Main beam lights. The blanked off original fuse box hole can be seen top left next to the steering column bracket. The connectors at the bottom left are new connectors for the ignition and stalk switches as well as a couple of connectors for the dashboard (more on this later).

new wiring WIP

The hinged panel turned out to be a bit flimsy since it was made from 2 layers of trimboard and hinged on a piece of carpet.  I therefore decided to replace it with a 3mm aluminium panel and did away with the hinge idea. I fixed a wooden batten to the front of the A-post using P40 and screwed the trimmed panel to it with wood screws. In this position the fuses are relatively unobtrusive but still accessible on the (hopefully rare!) occasions that they will blow. With the relays behind the forward edge of the panel they can also be replaced without too much trouble. The finished result is shown in the picture below.

new fuse ali fuse panel

To tidy up what was becoming a rat’s nest of bullet connectors where the boot loom joined up with the main loom and where all the earth connections were being made (above and to the right of the steering column) I decided to make a terminal board of 12 x 6.3mm blade terminals. This was a piece of aluminium bent into a top hat section and bolted to the bulkhead using the bonnet catch fixing bolts. On the panel, I screwed 2 rows of 6 blade connectors with each row soldered to the other using some solid copper wire. This used up a lot less space than a bullet connector solution and formed a star point for all earths. The panel is earthed directly to the offside chassis earthing stud with a 44/0.3 wire (rated at 33A) and all other earths for the cabin and boot connect into it meaning that each earth is only 1 pair of connections away from the main earth thus avoiding unreliable and difficult to trace daisy-chains. This can be seen in the photo below (the wires in a plastic bag are for the interior light and are ready for the time when the windscreen frame finally gets finished).

earthing point

The wooden dashboard has been completely stripped and re-trimmed. The instruments have also had their bezels replaced and while I was doing this I stripped out the innards to check that everything was OK – which they were so just a clean, polish and bench test and they were ready to go back in. I renewed all the wiring mainly to get rid of the black wires but some of the terminals needed replacing as well. One thing that I didn’t re-use was the old bi-metal voltage regulator. The modern solid-state regulators provide a much more reliable solution and are not expensive.

To make it easier to wire-up, I decided to use two 9-way Mate’n’Lok connectors. This meant that all the vehicle wires going to the dash could be terminated at a connector and thus worked on separately. Similarly, the dash wiring could be completed on the bench and then offered up for mating with the rest of the vehicle loom at a later stage.  This won’t help too much in the future with dash removal since there will still be all the mechanical components to disconnect – speedo cable, oil tube, heater cables, air ducts etc. but once that’s done, the plugs can be disconnected and the dash removed from the car for any further work (hopefully this won’t be needed!). The 2 connectors can be seen at the lower edge of the dash next to the air-vent hole.

rewired dahsboard

The back of the dash still looks a mess when all the aforementioned mechanical parts are added but at least they are hidden from view when fully assembled. . .

central dash 2

. . . so that the car is starting to look like a car again!

refurbished dash in place

As mentioned in the first paragraph, in order to avoid the corrosion of the bonnet connections I decided to use two 9-pin waterproof connectors, one for the nearside and the other for the offside lights. I needed 9-pins so that I could feed each lamp and earth with separate wires. These wires then ran back to the area of the washer bottle where I could use bullet connectors without the risk of them being exposed to the corrosive muck being thrown up by the wheels.

This provides quite a neat solution – the two connectors are visible in the photos below just forward of the two bonnet hinges.

bonnet wiring composite

That just left the wiring in the boot which was pretty straightforward. The only downside is that the lamp cluster bulb holders are notorious for creating bad earths through the clips that hold them in place. I thought that I had found a source of new ones but although they were nice and shiny, the build quality was poor meaning that the clips came out of the plastic body when removed from the cluster a couple of times. So far, I haven’t found a reliable replacement so that part of the chapter isn’t closed just yet.

boot wiring off side

I also ran a wire so that a rear fog-lamp could be wired-up in place of one of the reversing lamps. I’m not a great fan or user of these lamps so I haven’t converted it yet but it can be easily done in future if deemed necessary.

Amazingly, the motorised radio aerial sprang into life when first connected up (after 25 years) but after one up/down cycle it gave up the ghost. The motor still ran but the aerial wouldn’t extend. More in hope than expectation, I stripped it down and found that the telescopic aerial is driven up and down with a nylon cord that had become detached from the wheel. I eventually managed to figure out how it was supposed to connect and with a bit of luck managed to get it greased up and back together so that it now works perfectly. Small victories like this keep you going!

boot wiring near side

Another modification I decided to incorporate was a power socket in the boot. I had already run a 33 Amp cable from the fusebox for this purpose and found an unobtrusive place for the take-off connector on the boot lid latch cover.

boot power socket

All the electrical stuff is now installed and working except the interior light at the top of the windscreen frame since the frame hasn’t been installed yet.

In the end, the actual rewiring was not that difficult but what took the time was the planning so that I could decide where the cables would run and what length of each colour wire I needed to order as well as the type and number of terminals and connectors that I would need.

And the added bonus of doing it myself is that I now have a completely new loom installed in all the right colours and that I completely understand . We’ll see how reliable it is once the car is back on the road. . .

The continuing story of the struggle to make this happen will appear in the next blog which may not be too long in coming (but then again, I’ve said that before haven’t I?)