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MG TD TF 1500 - Do I need a new wiring harness?

Iíve been following this forum for quite a few months now, but this is my first post. Iíve been very much impressed with the level of knowledge and enthusiasm of the forumís users. Iím trying to get my í53 TD that I bought in 1957 back on the road after collecting dust in my garage since 1983. Iím trying to use as many of the original components as possible, but Iím wondering about the wisdom of keeping the old wiring harness. Iíve looked in the archives but havenít been able to find anything on the topic. Whatís exposed under the hood is black with 59 years of grease and grime, the color coding is long gone, and the cloth covering is quite deteriorated in many places, but the actual wires and insulation that I have been able to inspect seem ok and the wiring hasnít been modified at all. Most of the connections need to be renewed and there are some bare wires exposed in the fender wells, but those things can be fixed without too much problem. Do any of you have any words of wisdom to help me decide whether or not I should replace the harness?

Thanks for any help you can give!

Joe Olson
J.W. Olson

Joe, I would say this is a question of taste and ambition.

As long as everything works, why go through the pains of installing a completely new harness. My wires look rotten (most likely the original harness) + some loose wires installed by a PM (previous mechanic) who took the car apart and reassembled it. But everything has been operational for the last 6 years (thatīs how long I have the car).

I am an electrical engineer and this certainly does not fulfill my expectation of a decent wiring ( I even made some wiring harnesses myself in my early training days), but so far Iīve left it alone (just fixed some joints where two cables had just been bent together and isolated with some tape - that went too far ;-)

Thereīs good reasons to install a new harness, since old wires may break and touch the metal somewhere, but as long as it works I usually stay with "if it ainīt broke, donīt fix it".

Iīm sure there are some older threads in the archives about how "easy" it is to replace the harness, make sure you look at that as part of your decision making :-)

Mike Fritsch

I agree...there are so may vagaries and complications and dissassmbely troubles to do this ...

Why not go instead for tidying up the the covering. You can get some nice black fabric 'self welding' electrical tape. May not be ogiginal but gives you more time to do essential jobs :-)

Dave Moore

Welcome Joe, glad to have you aboard. I'm going to take the other road. I'm in the put-it-back-together stage of salvaging a 53 that last saw the road in 1972.
( There is no way that I would consider salvaging the original wiring. Under the wrappings are many cracks in the insulation, just waiting to let the smoke out of the wires. Seriously, the motion and vibrations of a being-driven TD could well expose wiring weaknesses that aren't obvious to a casual observer. I just don't think it's worth the gamble. Bud
Bud Krueger


If you decide to go with a new harness look under the Electrical heading in my web site list for some suppliers of wiring harnesses. Rhode Island Wiring has been used by several members of this forum.
No financial connection with same.

Also check the rest of Bud's site for eccellent T-series info.

James Neel

Joe, With modern test instruments, which are fairly inexpensive, I would test the wiring and see if there are any breaks or voltage loss. The outer fabric harness covering being bad doesn't mean the wiring it's self is bad. If you were going to do a chassis off restoration, I would say replace the wiring with new, otherwise if all checks out ok, I'd just clean up all the connections and get to driving the car. It's a lot more fun! JMHO. PJ
P Jennings

The "bulk" of my harness was good. Bad splices where fenders and such had been removed over the years, and of course, all the bullet connectors were a mess. I took the approach of re-shething the main harness (Nylon mesh), adding extra fusing, switching and some other mods such as test points.
In hind-sight, might have been better off starting with a new harness. Ran all new wires to lights (W/grounds) and such keeping all my conections "inside" the car this time, so I am confident it will last for a while.
(Some pics on Bud's TTalk site above.)
Mainly it all comes down to what you feel comfortable taking on.
BTW: I re-did mine to neg earth. I'll get some argument on this but, for me, that made adding fusing & switching to lights and other things easier for me to deal with.
David Sheward

David, I also converted to neg ground recently. Easy enough and now I can use appliances in the cigarette lighter just by plugging in, and my LED daylight driving lights do not require complicated re-wiring. Not visible to the naked eye unless you look at the battery connection, so I donīt think this distracts from the originality of the car.

Btw, I tried to make sense of all the discussions about corrosion being better with pos. ground, but in the end was not convinced it makes much of a difference...

Mike Fritsch

Getting all the butt conectors "inside" I think has helped a lot. I purchased new Lucas soldier type connectors from Triple-C. Gold plated, and makes it real easy to isolate a circuit to trouble shoot.
On the old harness the corrosion had gone back about a foot from all the connections running Poss ground, so you would be hard pressed to convince me it made a lot of differance. Been this way for over 10 years and with a bit of dilectric grease I have no corrosion on any of my connections so far.

I have a "problem" with multi coloured butt connectors, (car was loaded with them when I purchased it). I think what I ened up with looks very "period" and used crimp on's only where they can't be seen on bottom of my switch panel for extra fusing. Left the orginial fuse block in place and hid the rest.

If you go to TTalk & click on the pic of "Izzy" it will take you to some of the mod's posted there.
David Sheward

Thanks for all your thoughts. I think I'll check the wiring out visually and, following PJ's suggestion, test for broken wires and high resistance, and if it all checks out ok, stick with the old wiring. I share Bud's concern about unseen problems so I'll be pretty cautious about it. My car, TD23004, incidentally, is just a few days older than Bud's 53, having been built on 11 Dec 52, but my old wiring doesn't seem to be as deteriorated as what I could see on the photos he's posted.
J.W. Olson

"Most of the connections need to be renewed and there are some bare wires exposed in the fender wells"? Other than that, it sounds just great! The Lucas smoke sounds ready to escape. If you are having to redo most of the connections anyway, just replace the rotten mess. Consider not much is fused, and most all circuits are wired hot with the switch completing the ground. I would strongly suggest a new harness. Moss often has sales, and the PVC covered one is not that expensive. Just my opinion. George
George Butz

Wiring is pretty easy, especialy with a new harness. If I were restoring the car, I would go new, with braided coverings. For a few years at least, it will look wonderful. I'm amazed at how much the braid fades in the UV on my car which is driven frequently.

If I were simply maintaining the car (and original is becoming a sought after trait, I understand especially in Europe) I would repair as needed.

If the braid is in decent shape and not crumbling, you can take a very soft wire brush and clean it gently. You will be suprised at how it freshens an old harness.

A bit of solder to tin ends, some new bullet connectors and some dielectric grease will work wonders.

good luck!
Dave Braun

While doing my body-off work, I pulled the old harness....
In fairness to the old one, it was all working...BUT, so many cracks in insulation that it's amazing no electrical disaster took place....
Not only that, but you could not identify any of the colors, so navigation , while tracing problems , was a nightmare.
I decided to go with the more modern covered wire, as my car is not concours , anyway, and won't be as long as I own it....I just like the idea of having more modern materials covering the wire...It's cheaper , as well.
By the way, you can buy the instrument/dash wiring, alone, from Abingdon Spares, for about $85...Not a lot of wire, but it will save lots of time.
E.B. Wesson

Thanks again for your helpful responses. It is, of course, the specter of a mushroom cloud of Lucas smoke billowing from my car that prompted me to ask the question in the first place. My job now is to weigh the likelihood of hidden defects in the old harness causing big trouble vs. the cost and hassle of replacing it, as well as the loss of originality. In any case I plan to add extra fuse protection for major circuits.
J.W. Olson

If you have to replace the brake light switch, the new ones aren't as good as the older ones and seem to burn out in a short time. Dave DuBois came up with the idea of adding a relay to the system and avoiding future problems. Here's a PDF with illustrations on the subject. PJ
P Jennings

Joe, see for images of where and how I installed Dave's system. Bud
Bud Krueger

Re: Extra fuses

Everything on the car that could suffer an internal short and take out the wiring is already fused. The real key to longetivity in the wiring harness is to repair any grommets where the harness passes through a fire wall; keep the insulation on the wires intact; keep any spade connectors (of which there are few) solidly crimped; tin the wires that go under grub screws to prevent stray wires from touching something they shouldn't; repair any ground points and clean all bullet connectors so they don't build up heat instead of pass current; and provide isolation between closely mounted ground and hot points (the inspection light sockets come to mind). Otherwise there is nothing to really cause a short... IMHO.

Reinstall all connections with dielectric grease.

Oh... and make sure your pertronix wiring in the distributor, if you are so equipped, CAN NOT rub on any thing and cause a dead short to the housing. That will burn up the white wire all the way to the key switch. So use a tie wrap to keep it in place and inspect the wiring frequently.

Dave Braun

Dave, are you sure the head/tail/parking lamps are fused? I don't have a diagram handy at the moment. Good point about the Pertonix wiring- I'll check mine. BTW, I think Dave DuBois has an excellent write up somewhere about preparing grounds and connections. George
George Butz

See for Evan Ford's work on fuse panel installation. Bud
Bud Krueger

George, you don't want fused headlamps if you drive after dark. Heat type fuses are what are typical on headlamps but are rarely fitted on our cars. Sidelamps aren't fused, but the wiring simply needs to be protected from shorts with grommets and tinning. That said, my side lights are fused behind my panel. ;)

Dave Braun

Still running the original harness in my 1951 TD. I did replace some of the damaged or missing cloth covering in certain areas with black friction tape wound around the harness and tied off at the end with a small black nylon wire tie. Friction tape, available at hardware stores, is a fair representation of the original black cloth covering.
John Quilter (TD8986)

This thread was discussed between 30/03/2012 and 01/04/2012

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