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MG TD TF 1500 - Wiring burning

I drove my 54TF yesterday. When I put back in the garage I noticed smoke coming from around the right rear wheel. I got down and looked and the taillight wiring had actually melted. All the copper wires were explosed. Both tail light housings were very hot. I had not had the lights on but I felt of the light switch housing it was very hot. Anyone have an idea as to the cause?

On a second note some of you have talked about changing to electronic ignition. Moss shows an electronic distributor(very pricey)and pertronix ignitor electronic ignition. Which one of these is being discussed? Thanks for any help.

Bud White
S.A. White

Bud,
Check your brake light switch.
No lights on and both lamps hot ...that would be first place I would look!

I have been real happy with my Pertronix ...no experance with the Hi$ unit.
David Sheward

If your lights were off, then the only "hot" wire in the bundle at the rear of the car is the fuel pump wire #9, so perhaps the insulation some how failed, and this was connected to ground thru the wire to the lamp.
Or if the brake light switch failed closed the wire # 14 to the tail light would be hot. A short then could also fry the wire.

The rubber insulation on these old wires is usually hardened and often crumbles, particularly if heated as passing near the exhaust pipe.
this leads to internal cross connections and shorts in the harness.

A mystery!

In any case a new wiring harness is in order because you don't know the condition of the wires in the bundle, except that some should be fried.

It sounds like the wire from the light switch to the right tail light was drawing excess current over its whole length casing damage the entire length.
Don Harmer

I agree with Don- if there is melting to that degree, the harness could be internally melted somewhere else. If your dizzy is in decent shape, no reason not to install the Pertronix. No clue why the light circuit would melt if the lights were off. George
George Butz

As to the pertronix buy it from the co. direct. A lot cheaper than Moss. I have it in my 51 and love it. I also kept the old plate nad points and have it rigged so that in case something goes wrong, I can just plug them in and on the road again.
Tom Maine (TD8105)

Guys, remember --it's only the negative ground Pertronix units are plug-and-play reversible. Positive ground units needed wiring changes. Bud
Bud Krueger

Bud
So if you buy the Pos.ground Pertronix, it's not ready to install?....What has to be changed?
Edward
E.B. Wesson

The negative ground version acts just as a set of points and wires in the same way. It switches the low end of the coil to (and from) ground. Just like points.
The positive ground Pertronix is connected between the coil and the negative (ungrounded) wiring. You have to add a wire connecting the 'low' end of the coil to ground. The Igniter is then connected to the 'high' end of the coil.

See http://www.ttalk.info/Tech/pertronix_igniters.htm for more detailed info. IMHO, next to swapping in a 4.3 rear end, a Pertronix Igniter is one of the best things that you do to a TD. Bud
Bud Krueger

Refering to Buds comments above -- That says to me that the positive ground Pertronix units are actually the same as negative ground units but are wired into the car in a different way. So the current goes through them in a proper direction for the transistors inside.

Anyone care to comment??
Bob
Bob Jeffers

Absolutely right, Bob. The Hall-Effect transistors are standard units, just wired differently. Bud
Bud Krueger

Bob,
Don't think it is the same unit.
Different model numbers for poss or neg ground as well as type of dizzy.
David Sheward

I stand corrected!
I'm really glad I did this 10 years ago and it works because in the last month or so I have really gotten confused about it!
LOL
David Sheward

WHOA! Do not get the idea that you can take a negative ground Pertronix unit and just futz with the wiring to turn it into a positive ground unit. One of the wiring connections is made by screwing the mounting plate into the distributor. Buy the proper unit, please. Bud
Bud Krueger

I do not wish to add to my confusion, but
seek clarity. I am thinking about installing
the Pertronix Elec Ign on my Early 1950 MG TD
(0823) which is Pos/Gnd with an asymmertric dist.
P/N LU-146 MP12 Or MOSS 222-561.

Is this a simple swap (plug & play) or is additional
wiring and head-standing needed....?
Which is best: Set timing at idle or at 3000 rpms.
Would the Lucas Sports Coil p/n Moss 143-200
be of benefit too....?

I've read/heard horror stories about the Pertronix
installtion and then the first turn of the key,
then the cranking, and finally, the smoke from
wires and burning plastic emerge from the bonnet....!

I keenly want to avoid that.

I seek clear, accurate advice and not bus-stop gossip.


Your thoughts, please.

TIA.


DrRx.
drcrougeux

It has been a couple years, but I recall my positive ground system came with great instructions and a wiring diagram. You have to fabricate a short wire from one coil terminal to ground, then wire as directed (see Bud's post above, he explains it well). Although I have never had a failure, I take my points plate with the original wire to the coil with me. I put an eyelet loop terminal on one lead from the Pertronix, and used as small screw/washer/nut to attach to the existig terminal from the harness that formerly went to the coil, taped it up of course, That would allow a quick switch back to the point plate. George
George Butz

Easy, Doc. One thing at a time.
1) If your distributor has an asymmetric cam and is in a positive ground system the Moss 222-561 would be the correct unit.

2)NO! It is not a simple swap (plug and play). Yes, you have to add a wire to complete the installation. Check out http://www.ttalk.info/Tech/pertronix_igniters.htm and look at the page about installing a positive ground system. It's easy. Just follow the directions.

3) Setting the timing and changing coils are separate issues.

4) As with any hi-tech item there are bound to be out-of-the-box failures. But, my experience has been that by far most of the folks that let the smoke out of the wires are those don't follow the directions.

I have no involvement, or interest, in Pertronix except for my belief that it's a good product. Bud
Bud Krueger

Bud, you might want to take a look at this site to protect your wiring. http://tseriesmg.blogspot.com/ It seems to make sense this may have prevented your wiring short. I rewired my TD and it seems to have worked out well. I still use a battery disconnect just in case.

Bill
Bill Brown

This thread was discussed between 26/08/2011 and 29/08/2011

MG TD TF 1500 index

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