TR3A Installing a New Wiring Harness

[David Owen]

One of my winter projects will be to replace the wiring harness in my TR3A.  The car has been converted to negative ground.

Does anyone have a really good methodology for performing this replacement?  The current wiring has been jury rigged so much that I can't rely on it.

One of the options I did find was to lie the new harness out on a 4x8' sheer of plywood and start labelling everything from the schematics.  But I am not sure this would work due to all the changes that have been made?

Any ideas would be welcomed.

[EliTR6]

I printed out the wiring diagram, laminated it and spread the whole loom out on the living room floor 

I spent ages with a multimeter figuring out where each wire ended up and labelled both ends 

Once you get the main part of the harness through the grommet of death in the bulkhead, the rest is easy 

I also replaced all bullet connectors with the spade type and shrink wrapped each one. I bought a decent crimping tool for the job, its already earned its keep! 

[David Owen]

2 hours ago, EliTR6 said:

I printed out the wiring diagram, laminated it and spread the whole loom out on the living room floor 

I spent ages with a multimeter figuring out where each wire ended up and labelled both ends 

Once you get the main part of the harness through the grommet of death in the bulkhead, the rest is easy 

I also replaced all bullet connectors with the spade type and shrink wrapped each one. I bought a decent crimping tool for the job, its already earned its keep! 

 

Thanks, Eli.  Did you solder and crimp?  This will make for an interesting negotiation.  It will probably end with me working in the laundry room.

Edited September 13, 2020 by David Owen

[foster461]

David, I replaced the wiring loom during my TR3a project. It is a simple loom and once you figure out the layout of the major segments, how they are routed and what grommets they need to go through things pretty much fall into place. The two areas that need some attention in a standard LHD TR3a is the wiring behind the central instrument panel as there is a lot going on and there are several patch wires that may not appear on any wiring diagram. I think I documented most of not all of these. There is also the funky loop back connection near the RHS horn that exists because the loom is multi-handed and when used on a LHD car it needs to be configured correctly. We can help you when you get to that stage and wonder why you have two empty connectors. If you have other special stuff going on you will need to deal with that too but compared to a modern car this is a piece of cake.

Stan

[EliTR6]

6 hours ago, David Owen said:

 

Thanks, Eli.  Did you solder and crimp?  This will make for an interesting negotiation.  It will probably end with me working in the laundry room.

Just crimped but with a proper tool (approx 60eur) and taking the time to do it properly. I read up on the solder/no solder at the time and the reasons were a proper crimp should make a strong but flexible cold weld whereas soldering heat can make everything a bit brittle and the wire could eventually break off. 

Really it just boiled down to the crimped terminals feeling strong enough and not wanting to spend ages fiddling with a hot soldering iron.

[Lebro]

I agree on a proper crimped termination is better than a soldered one when subject to any vibration. Personally I would leave the bullets on, they will be brand new & will be perfectly OK for a long long time.  Wiring on my car is a new standard loom, with extra wires added by me, as required, I use the blue insulated crimp bullets to mate with existing connections, & a ratchet type crimping tool.

Bob.

[ianc]

The loom for my TR4, 4VC, was made by a technician from Lucas in 1962 to the requirements of the drivers and navigators in the Works' team. 

Bullets throughout and almost all wire colours had faded by 1992.  As Neil Revington, "doesn't do electrics" and the car has 20 fuses (four SF4 boxes), lots of relays and extra equipment,  I laid the whole loom on the dining room floor in 1992, put a cable marker on the end of each wire, and it was re-installed after the re-build by Neil & Carl. 

I have never had any problems whatsoever with the original bullet connectors.  The rubber sleeves can deteriorate, but they can be replaced.

I agree with Bob, crimping (with use of proper tool) is better if the cable is subject to movement/vibration in the area of the connection.

Ian Cornish

[David Owen]

I am leaning toward crimping bare spade connections and then shrink wrapping them as opposed to the ones that come covered.  Any preference or advice?

[foster461]

David, the theory is that crimping is better however for a good crimp connection all of the planets have to align - wire, connector, crimp tool, technique.

I have found I can reliably solder better than I can reliably crimp.

Stan

[Ralph Whitaker]

I bought what I thought was a professional crimping tool. I already had 2 but they were both for the coloured plastic sleeved terminals. The new one I bought came with different sets of Jaws but the tool itself was the same as the 2 I already had. However one of the jaws was for the plain brass spade connectors and made a really good crimp, folding the ends of the tangs inwards as it crimped into the wire and to grip the outer plastic of the cable. The main problem I had was finding any good quality terminals, they seem to be made of much thinner brass than the good old Lucas items, and many had to be squeezed with pliers to get a solid grip on the male terminals of the switches etc.

For all the inline connectors I used soldered brass bullets as original.

Ralph

[tthomson]

I totally agree with the comments on crimping for spade connectors and soldering for bullet connectors.

I use only uninsulated connectors when crimping, with separate insulated covers, and I use a decent crimping tool. The preinsulated crimpable terminals are not worth my effort. (they are unable to hold the connection well enough).

I typically purchase my connectors from Vehicle Wiring Products. These connectors have proved to be very reliable (so far)

As Foster461 says I solder Brass bullets.

As with all connectors they always need to match the cable size to be effective.

TT

Edited September 14, 2020 by tthomson

[David Owen]

I received a PM that gave me the idea to leave a couple of inches of wire on everything I have to detach (instruments etc.) to indicate what goes where when I start to reconnect everything.