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MG TD TF 1500 - Electrical Issues

Hi All
I'm hoping someone has some insight for my problem. I have a 53 TD I restored myself, all new wiring harness, new generator rebuilt battery, new voltage regulator. Original ignition switch. I have been having some electrical problems for the last year that have been getting worse. The car was not charging consistently and the new regulator seemed to help but not much. Last year I drove the car one day and after parking it I walked past and the car smelt hot. The generator was very hot. Disconnected the battery and changed to new generator and that seemed to fix it. This year I fitted a new battery.

Second drive of the year was yesterday, and I was out for about a half hour, everything seemed good. When I parked and switched off I noticed the charge light stayed on after the switch was off and the ammeter was showing a hard discharge. I figured a short somewhere. Removed the ground from the battery and checked everything. Only thing I found was the lead to the starter was loose. Tightened this and reconnected the battery. No discharge showing. Tried to start and sparks and smoke from either the ground wire or the voltage regulator. Now the car will not turn over and every time I try I get either a click or a spark from the same area. I"m not sure where exactly.

Thoughts?

Joe Hine
J.D. Hine

There are some EE's on this board who will no doubt come up with the source of the problem Joe. Id suggest going right over the car and checking all of your electrical connections for security. If that checks out my guess would be the new voltage reg. I'd heard that there were issues with some of these. The progressive worsening is a clue. Maybe swap it over with a known serviceable unit. Where did you get the new VR and genny? Cheers
Peter TD 5801
P Hehir

Make sure the frame to bellhousing/block ground strap is in place. If the "cut-out" in the regulator sticks, that would overheat the dynamo and cause serious discharge. Do you mean the engine will not spin over at all? The cranking circuit has nothing much to do with the rest of the electrical system. George
George Butz III

Hi George and Peter. Thanks for your replies

Yes the engine will not crank at all, I'll check the ground strap tomorrow, but I'm sure it is there. Peter the generator and VR are from Moss

I have to say, I"m all little suspect of the ignition switch. I'm going to check that tomorrow, and order another new VR.

Joe
J.D. Hine

Someone on the BBS will probably have an original VR that they could help you out with. I guess yours is a 6 post? It seems just too many AM parts have issues. If your fairly new one is a dud you might just end up in the same boat. If you do have to replace the switch, original reconditioned ignition switches are available in the States from Craig Seabrook and should be good for another 50 or more years. They look correct as well. If Craig can't help you I also have a few restored MRN (TC and early TD) and FA (later TD) series LUCAS PLC 6 switches, though shipping from Oz isn't cheap. Cheers
Peter TD 5801
P Hehir

Hi Joe, I had a similar experience much like yours. I switched the car off and as I was getting out of the car noticed the Ignition light was on and about the same time smelled something burning; it was the wiring going to the generator. By the time I disconnected the battery it was too late, smoke was out.
The VR had shorted and was sending power from the battery directly back to the generator. I replaced the VR and wires to the generator.
I remembered reading an article about this happening but promptly forgot about it until it happened. The article suggested installing a 35 amp fuse on the Brown wire from the starter switch to the ammeter. I installed mine just before the terminal on the ammeter.
Hope this helps.

Ed
TD/20709
ECS Stanfield

The starter circuit is totally isolated from the rest of the wiring. Very simple- Ground side: Battery cable to side of battery box/bulkhead, cable from bulkhead mounting bolt/chassis to bellhousing. On the hot side, just hot from battery to switch to starter. You could remove the brown wires from the starter switch and that would isolate the rest of the car's wiring. If it won't spin over, there is a bad connection - ground, bad starter switch, bad battery or starter. You can take a jumper cable and go from battery ground terminal to a bare metal spot on the block, or even starter mounting bolt to eliminate all of the possible ground problem areas. Shorting across the starter switch would make it crank if that is bad, etc. Sounds like similar problem initially that Ed had. Inside the regulator, one side/coil regulates voltage. The other side/coil is a spring loaded contact called the cutout. When the generator voltage is higher than the battery it closes, thereby charging the battery. When generator (uh, dynamo) voltage is lower than battery, it is suppose to open to prevent current from flowing backwards from battery to generator. If it sticks, full battery current will be flowing through the stopped dynamo, which will cause things to burn/melt and the Lucas smoke to leak out... George
George Butz III

You mean like this George? Recognise this Jasper? Cheers
Peter TD 5801

P Hehir


Guys, thank you for all your replies. I'm going to order a new voltage regulator as a first step, it seems to me given the history that I will find that is the problem. I'll let you all know.

Joe
J.D. Hine

Peter,

Sure! Bad memory but fortunately all turned out well.

Thanks for sharing again!

Jasper
Jasper Nederhoed TD3966

As others have said it looks as though your cut out is not working properly. The dynamo can work either as a generator i.e. outputs a current when the pulley is spun, or as a motor if current is supplied to it. The cut out is effectively a one way valve that allows current from the dynamo to flow to the battery but not vice versa. Without it, when the engine is stopped current will flow from the battery to the dynamo which will try to turn as a motor. It can't do this because of the fan belt so everything overheats. The cut out switch is to the right hand side, under the regulator cover. As a rough check when the engine is not running the contacts above the right hand coil should be open. When the engine is started and the speed increased the contacts should close. Stop the engine and they should open again. Circutary associated with the cut out also switches off the red charging lamp on the dash as the contact close.


Jan T
J Targosz

This thread was discussed between 13/06/2018 and 18/06/2018

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