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MG TD TF 1500 - Ignition/electrical mystery

OK, here’s a weird one – I thought I had a problem with the starter switch on my TF – often the ignition light would not go on with the key, and the engine would not fire even though the starter worked fine. Sometimes the engine would start up but die after running a while (sometimes a minute, sometimes an hour), and the ignition light would not come back on. So I had the ignition switch replaced, but here’s what happened on the way home from the shop:

Car started fine right off the bat. I stopped, parked and restarted several times on the way home with no problem at all. After about 25 miles and an hour of driving, however, the engine cut out and the ignition refused to work, just as before. (I got it started again, basically by hot-wiring, and then parked.) An hour later I tested the key in the ignition again – no light (the starter motor turned over vigorously, but there was no ignition). Another hour later, I tested the key again with the same result. Then, to show a friend that the battery was fine, I switched on the headlights – presto, the ignition light also came on, and the car fired up with no problem.

I found, however, over the next few hours that this simple "solution" did not always work – but by playing around with the lights, the key and anything else I could think of in various different combinations, I could eventually get the ignition to work. The engine remained susceptible to cutting out, however, and in the end I couldn’t get it started without hot-wiring.

Obviously there’s something wrong with my electrical system and I’ll have to get an expert to look at it, but does any of this sound familiar to anyone?
Ian Watson

Also, sometimes I can turn the headlights on without the key in the ignition or the engine running, but usually (1) they will only only light up with the key turned on or, (2) without the key, they will light up if the engine is running and revved but will dim out as soon as the engine speed drops.
Ian Watson

Sounds as though the wire from the battery to the starter switch is good, but there is a problem with the connections from there to the rest of the system. You should be able to track it down with a test lamp while it is in the failure mode.
George B.

As noted above, the cranking (starter) circuit is separte from the rest of the electrics. Things to look into: pull fuses and clean curved contacts on fuse block. With car running, wiggle/pull wires under hood, and carefully under the dash (this is called "pull testing"). If it dies, you have narrowed down the trouble. Although my wiring diagrams are at home, I believe the headlamps should work regardless of the position of the ignition key. Trace current paths on the wiring diagram to a common point- for the switched items and the lights- that may be the problem spot. I think all of the current feeds off of the starter switch (two brown wires). The ammeter also feeds everything. Check connections there as well. Bad grounds are notorious for weird problems- there are black ground wires from the harness by the regulator/ground battery cable end, behind the metal dash panel, etc.- have seen a newly painted part insulate, etc. If nothing found as above, get a test light (stick tester)- has a clip on one end, and a metal point on the other. While in failure mode, ground the clip, and figure out what is hot, and what not- this should lead you to the trouble. Lastly, as not much is fused in a t-series, I would suggest not driving the car, as it could burn if a short or loose wire! Also, if you are not comfortable doing the sleuthing, have someone else give it a shot.
George Butz

I once had a similar problem, though not identical. There are contact strips on the underside of the regulator, and with the passage of current one would touch ground and prevent ignition from working - while lights etc. could work. I would start the car with a wire, which would cool the strip and break the contact. It took me a while to finf that, but by reshaping the strip I eliminate the problem. Not that the regulator was a new/refurbished item. I would not hurt if you check that: watch for any strip that runs close to another contact.

Denis
Denis L. Baggi

This thread was discussed between 20/07/2000 and 28/07/2000

MG TD TF 1500 index

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