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MG TD TF 1500 - Prince of Darkness strikes...Help Please

Here's the weird problem...My TD ('52), has all new wiring....
I carefully checked all the connections with an ohm meter, before startup.
Engine works fine, generator does it's job...Car runs great.
headlights, tail lamps , parking lamps work (car does not have turn signals installed).My separate fog lights also work (through a relay).
First problem: My fuel warning light stays on...Sending unit is correctly installed, and , with a nearly full tank, ohm meter shows no connection from stud to ground. Stud is connected to proper green wire. If I remove green wire from stud, fuel light goes out...If there's no connection from the stud to ground,(according to the meter), how can this circuit be completed to light the fuel indicator.?
The sending unit was tested and working when I re-installed it after paint.
Second problem I have tail lights (as mentioned), but no brake lights...Shorted across pressure switch, but still no brake lights.
Looking at the wiring diagram, both circuits terminate at A4 ...Is this a clue, or just a coincidence? I'm assuming (HELLO!), that the green circuit is the stop light, since it goes to the pressure switch.
Thanks for help tracking these dastardly gremlins.
E.B. Wesson

Edward, the wire that gets attached to the fuel level sensor should be green with black (#24), not green (#17). A green wire (#17) does go to the stop light switch. Can you find the #24 wire? The brake light wire (from the pressure switch) should be gree with purple (#22). I can think of no reason for a green (#17) wire being back at the fuel sender. Bud
Bud Krueger

Thanks for your input...I will double check, but I'm pretty sure my fuel sender has the black tracer...It's the wire that came on the ready-made harness, from Moss.
I'm also pretty sure that the purple tracer is on the brake switch....
Going back out to the garage now to go back over those.
If wiring is correct, where else should I look?
Do you think adding a ground wire to the fuel sender might make any difference?
E.B. Wesson

Edward, the fuel sender gasket set sold by Abingdon Spares (shown below) contails a small annular gasket that goes around the post on top of the sender. Without it, it's possible for the green/black wire to contact the tank and keep the light on.
Unless you have a plastic fuel filter in the line you don't need a ground wire. Do you have a test lamp handy? If so, connect it to the green wire on your brake light switch. It should light up when you turn the ignition key on. If so, move it to the other terminal on your switch, turn on the key and step on the brake. Does it light? Is that where the green/purple wire is? Bud

Bud Krueger

Thanks for your suggestions....
Spent the day analyzing my problems...
Found two reasons for the brake-lite problem:
1) Only car I've ever owned that requires the ignition switch to be on for the brake lites to work!
2) Driver side (LHD) tail lamp unit has gone bad...found voltage all the way to the connection on the unit, but corrosion inside the spring-loaded connector, prevented a connection to the bulb...
I took it apart, and cleaned it. It now works, but I'm going to get a new one, as this one is worn out.
Regarding the fuel lite....I have a spare sender, and took it apart...I can now see that the stud is connected on the inside to a brass tab, that will turn with the lower nut, and ground inside the unit.....
I will have to wait till I'm low on fuel, and open the back of the unit, and adjust the connector....A rather stupid design, IMHO, since you can easily move the internal tab, when you attach the wire to the stud.
The good news on all of this, is my wiring is correct.
E.B. Wesson

Bud may be on to something with the sender- if the insulator washer is damaged, perhaps tightening the nut causes it to short. Missing and it will short for sure. Of course my pictures of the sender are at work or I would post, maybe Tues. George
George Butz

EB, Where are you in GA. I'm about 150 miles north of Atlanta.

J K Chapin

1) Only car I've ever owned that requires the ignition switch to be on for the brake lites to work!

I meant to add that I just discovered this last weekend. Weird but I suppose thoroughly British.

Tea and scones all around :-)

J K Chapin

Edward, that's why I said "...turn the ignition key on..". I recall spending a long time chasing down a brake light problem until I learned that. Bud
Bud Krueger

"Only car I've ever owned that requires the ignition switch to be on for the brake lites to work!"

Green circuit (green wires) - Switched, fused circuit. The green circuit is fed by the white circuit - switched, unfused circuit (true for all MGs and I believe all early British cars). Cheers - Dave
Daved DuBois

Ed, there should be two nuts on the sender. The inner one should lock the stud/internals in place. The outer one then tightens the wire loop without moving anything internally.
George Butz

PS- in order from the case outward, there should be the insulating washer (the small green one in Bud's picture or equivalent), flat washer, nut, then another flat washer/wire terminal end/flat washer/nut. The origianl units also had a bakelite insulator on top of the first insulator washer. So if the innermost nut is tight, attatching the wire won't move or effect anything. George
George Butz

Ed, I had a similar problem with the fuel light. My problem came about because I installed the fuel float assembly upside down in the tank. The light would go out when the fuel level was low. You might want to check that.

Bill Brown

Thanks again for all the comments...
The stud has the "proper" number of washers....It was new when I installed it into the tank....The float is in the correct orientation....
I discovered, as mentioned, that if care is not taken, that the lower nut can turn when tightening the upper nut...That in turn, turns the inside connector, and it will ground to the case...I tested my theory, by removing the wire, and top nut, then moved the lower nut slightly.
The meter then showed no connection, and when I put the wire on, the lite was out....Trouble was, that as soon as I put the top nut/washer, back on, the lower nut turned just enough to ground the connection....
Easy to fix, but must drain the tank first....I will just use up the gas, until I get down to a point below the sender, then take the four back screws out and adjust and tighten the stud...

I'm in Hiawassee, 110 miles N. of Atlanta, and 60 miles (or so), West of Westminster.
E.B. Wesson

This thread was discussed between 18/11/2012 and 20/11/2012

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