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MG TD TF 1500 - Engine and lights die together.

Folks, the dear old TD has developed an interesting trait. She fires first time and runs sweetly, at all speeds. But then randomly (by no means every time - only about once in 50 slowdowns) as I slow right down for example at an intersection, I suddenly realise the engine has died, ignition and dash lights dead, all exterior lights dead and fuel pump silent.

I switch off the ignition ... take a breath ... ignition back on, and she fires first time and scampers off as though nothing has happened.

Early investigation suggests:
Battery leads secure.
Earth straps secure.
Leads to coil secure.

Anyone had anything similar, or any suggestions as to what I should investigate first?

All advice gratefully received. Regards, John.
J P Hall

Check the ignition switch. This is going to be a real bear to find as it is intermittent problem that only happens periodically. I think that I would probably start by tapping the ignition switch then next time it happens or pushing on the key. There is a nut on the back of the ignition/light switch, with a glob of solder on the nut/screw and it is quite possible that the solder has allowed the nut to back off a bit. Cheers - Dave
DW DuBois

After nearly a year of a similar problem in my YT & lots of troubleshooting, mine was an internal fault in the ammeter. I bypassed it by connecting both wires to one terminal & the car has now done nearly 2,000km without fault.

The gauge is still in the car, so I can't tell you exactly what is wrong inside, but I suspect a broken wire that gets hot when you draw extra current (headlights) and open circuits, then cools and remakes the connection !.

I rebuilt the ignition switch twice thinking that was the problem, and carried a "hotwire" to get me home (without headlights) whenever it happened.

Now the YT & TD have the same gauge, so worth a look I'd suggest John.

Cheers

Tony
Black Mountain Qld
Australia
A L SLATTERY

Well now, what a lot of food for thought. You're right David, I thought "ignition switch" initially, and have carried out a preliminary exam, without finding anything obviously loose. More on that this weekend. Tony's experience reminds me that the TD's ammeter does lurch to pos quite a bit, possibly hinting at a developing internal fault. I might plumb in the ammeter from the (hibernating) TC to see what happens. As a matter of interest Tony, could you not have just bypassed the ammeter completely instead of connecting wires to one terminal? - perhaps I'm missing something.
Thanks both for your suggestions. Regards, John.
J P Hall

Connecting both wires to the one terminal does the same thing John, effectively bypassing the ammeter. It's the same as joining the two wires together using some sort of electrical connector, only a bit neater. Cheers
Peter TD 5801
P Hehir

Gotcha Peter. Incidentally, the backlight on my ammeter is so dim, I don't even know it's there at night! Looks like the time has arrived to fix both problems, if Tony's diagnosis is correct. John.
J P Hall

Suggest wiggling/pulling wires carefully while running under bonnet at starter switch and fuse/regulator area and under dash. If something loose or corroded or cracked connection you may find it. If you have a wiring diagram you can trace it back to most likely spots. Above good advice also. George
George Butz

John this is a pic of the ammeter in my TD as it sits in the dash. Although it's not visible in this shot I've fitted a multi pin connector into the harness so I could tidy up & ensure the security of all of the wiring at the rear of the dash, while it sits on the bench. Cheers
Peter TD 5801

P Hehir

Hi Peter,

What a shame that the distances between, and the colours of, the tie-wraps vary so much, otherwise it would have been quite a neat job..... ;-)
Willem van der Veer

The good news Willem is that once installed in the car no one will ever see it! And I have the satisfaction of knowing that everything behind the dash is totally secure. Worrying about the colour of cable ties that will never be seen is a luxury I can't afford & makes about as much sense to me as rearranging deck chairs on the Titanic :-) Cheers
Peter TD 5801
P Hehir

That's exactly what I'm going to do this weekend, George - highly technical wiggling and pulling, on an eliminative basis.
And Peter, I thought Willem (tongue in cheek) was very harsh. The photo will help me greatly.
I shall report back with any findings, in case it helps anyone with the same problem.
Regards, John.
J P Hall

Hi John,
If you examine the wiring diagram for the TD, you will find there is only one point in the system where a single failure can lead to loss of ignition and lighting - the ammeter.

To be in the lighting/ignition switch would require a simultaneous double fault - most uncommon !.

So it's either the ammeter itself, or the wire leading to the ammeter from the battery or from the ammeter to the lighting/ignition switch.

Just my 2 cents worth !.

Cheers

Tony
A L SLATTERY

Tony, you make a good point (as usual). The most likely and simple cause is what we always know to look for first ... so ammeter it is, after work tomorrow. I now understand that simply joining the opposing wires onto one post, will minimise the need for fiddly joining of wires away from the ammeter. I reckon that might confirm your suspicion - I'll report back asap. Regards, John.
J P Hall

Take care because if the ammeter terminals are a bit loose its very easy to make a short circuit to the ammeter body and then to earth, which can have dire consequences. I put a bit of additional insulation around those terminals to make sure.
Dave H
Dave Hill

The problem with jiggling live wires is just what Dave describes. I'd disconnect the battery before you make the change & not take any chances. Cheers
Peter TD 5801
P Hehir

Been indisposed for a couple of days, so probably won't be able to bypass the ammeter until the weekend now. But could any auto-elecs reading this tell me : is it feasible to have the power going through the ammeter as normal, AND run a joiner (3 wires, 2 into 1) to bypass the ammeter - thus hopefully keeping the car running and being able to monitor the behaviour of said ammeter? There might be a reason NOT to do this, and I'm only too happy to learn, especially where it's auto electrical. Regards, John.
J P Hall

John, once the ammeter is bypassed, it will not show any reading.
You could make a bypass that you can switch off to have the meter reading back, but that switch would need to be rated for 30 amps which most are not. And it would be another potential source of error.
Rgds Mike
Mike Fritsch

Thanks Mike - so even though the ammeter would still be receiving power as normal, the fact that a bypass line was operating at the same time would make it impossible for the ammeter to operate. No wonder electricity is a dark art.
So later this week I remove the wires from the ammeter and join them up using a suitably-rated joiner. Then like Tony, I see whether the car runs without incident. If it does, I need to have the ammeter repaired.
Next question: who repairs T Series ammeters??
Regards, John.
J P Hall

I shouldn't bother, my ammeter doesn't work properly either and its nothing lost. A voltmeter is more useful, but bulky and nowhere to fit it other than hanging under the dash. Instead fit a made for purpose voltage sensitive LED that changes colour with voltage and does the same job but takes up a fraction of the space at relatively low cost. Particularly recommended if you are running an alternator.
Dave H
Dave Hill

remember, your ammeter gives you a warning if you have a short. Gives you time to disconnect before you lose a valuable asset and an old friend.
These cars are not fused to modern standards.
Ray TF 2884
Ray Lee raybar2(at) tiscalidotcodotuk

Totally agree, Ray - that's why I want to confirm that the ammeter is at fault, and then have repaired. Hence my question "who repairs T-Series ammeters". I'll run it past the Aus. MG clubs of course, but otherwise send it somewhere if there is an experienced specialist overseas. It's what we do for these cars that we love. Regards, John.
J P Hall

True, but safer still not to run all that current up to the dash and back. A Voltmeter or LED takes virtually no current at all. Besides what are the chances that you will be looking at the ammeter at the exact moment something goes wrong. But everyone to his own.
Dave H
Dave Hill

OK - today I dropped the dash and revealed the wiring to the back of the ammeter. I hope to attach a photo showing evidence of heat damage (molten insulation) where the 2 wires enter the negative pole. These 2 wires were slightly loose under the grub screw - they were in place, but could definitely be wiggled. So before I set about isolating the ammeter, would any respondents be able to confirm whether loose wires (but in place in the terminal/post) would create arcing or something similar, leading perhaps to ammeter damage and the increasing failure of all electric power?
All advice gratefully received. Thank you ... John.
PS - photo not very good; the 2 wires zip-tied together for ease of reference.

J P Hall

John, the answer to your question is yes, you can have an intermittent circuit with a loose connection causing the problem you have bee having. I would even spray a bit of WD 40 to both clean and ensure a good connection.
Good luck.
Don TF 4887 "Figaro"
Don Walker

John I'd suggest using some heat shrink over the melted insulation & also tinning the wires ensuring of course that they will fit back into the terminal. Secure the wires & dash then take her for a drive. If the ammeter behaves normally & the fault doesn't reappear then you've solved your problem. Might be worth also checking the rest of the instrument wiring for security while you have the dash forward. Cheers
Peter TD 5801
P Hehir

If you are comfortable with a soldering iron, I would actually solder the two wires together before connecting them back to the ammeter. Thatīs one less potential source for a fault.
Donīt forget to apply the heat shrink before soldering them together (donīt ask me how I know)
Rgds, Mike
Mike Fritsch

Ha! Good advice thank you Mike. As we seem to be ad idem, I'll be cleaning the wires and the terminals, tinning, heatshrinking and reinstalling this weekend for a trial run.
The feeling in my bones is that we will have identified the fault (thanks again to Tony my fellow Queenslander) and rectified it .. but let's not get ahead of ourselves! Regards, John.
J P Hall

John, if you look at the wiring diagram in the Workshop Manual you can see how the brown and brown/white wires carry the power for virtually everything. Bud
Bud Krueger

If you want to protect against burnt wiring in the future, you can install a good quality "in-line" fuse in the supply wire from the starter solenoid to the ammeter.

I use a 35amp fuse, and it has saved the wiring a few times when a short occurred by accident or misadventure.

Mine sits near the solenoid, so it's easy to access near the battery.

You cannot depend on the ammeter to tell you when a short has occurred - you will smell smoke long before you notice the ammeter !.

I must admit I have not tested the 35amp fuse for the perfect storm - high beam headlights, horn & wipers - all at once !. I avoid driving at night in the rain on the highway.

Cheers

Tony
A L SLATTERY

Good idea Tony - I'll do the temporary re-fit of ammeter wires and test everything this weekend; then if all is ok, add the 35amp fuse for good measure. Regards, John.
J P Hall

Good news - wires cleaned, terminals cleaned, even the ammeter face and bezel cleaned, and then everything reassembled ... and bingo - she took off like a startled rabbit. No hint of a failure so far, and in fact I detect a return to full power, after a few sluggish runs recently. So the signs are that Tony's suggestion was spot-on. If all remains well, I will tidy up the wiring, apply heatshrink and once again give thanks for the detailed and practical help available to amateur restorers on this BBS site. Regards, John.
J P Hall

This thread was discussed between 18/05/2016 and 29/05/2016

MG TD TF 1500 index

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