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MG TD TF 1500 - 1953 TD factory turn signals (directionals

I am troubleshooting an electrical gremlin and I'd appreciate some advice.

The problem: When I step on the brakes the front side lights turn on (along with the brake lights).

Apparently there is a shorting out of two circuits (brake lights and side lights) somewhere. I thought it might be a grounding issue so I examined the tail lights but found no faults.

My next guess is a short internal to the turn signal relay (Moss number 141-400). Before I purchase one and swap it out, can anyone with relate any similar experience.

Thanks
Mark Sherman
shrmnmrk at gmail.com
Mark A. Sherman

You don't say whether this is a recently rewired car. If not is it a new problem that just came on recently?

If this is a new problem on a recently completed wiring, check that you have connected the 8 wires to the relay correctly.

The DB10 turn signal relay has been known to give the occasional problem. With the battery disconnected, remove the cover and inspect the contacts. Be sure they are not sticking. In any case, take the opportunity to clean the contacts with a fine emery paper.

Of course, the relay's function is to switch between brake lights and turn signal on the side where the turn signal is activated, so the relay is immediately suspect.
Lew Palmer

I have seen the cover on the DB10, scrwing upthe connections.

Peter
P G Gilvarry

You are correct, Peter. Mine, which has been in the car since before my ownership, has the numbers on the case exactly reversed - #1 as market is actually #8, and so on.
Lew Palmer

Mark, I have heard that the cover to the relay can go on backward. If memory serves there is a couple of tags that help to locate it the correct way round.
Here is the wiring diag to help try to trace the errant wire.

Rod Jones

The original DB10 cover has two tangs on one side and one tang on the opposite side that should line up with the base. Even ensuring the tangs were properly aligned with the base, the numbers on the cover of my DB10 was still exactly reversed.
Lew Palmer

Mark,
If you have a loom with the right colors.
This diag might help you identify which wire goes where.
Rod

Rod Jones

This one from the WSM should help with the others on the relay unit.


Rod

Rod Jones

Mark
I've had this problem with a faulty stop/tail globe (shorted out inside)
What happens if it is this, is that when you operate the brakes the power goes to the brake lights and it feeds the parklights through the short in the globe
Also there are some dodgey globes about that have quite long contacts on the bottom of the globe instead of nice short ones and when you twist them in they bridge the terminals in the light socket
If you've changed a globe lately it might be a dud
Best test is to remove the stoplight globes and see if the problem goes away without the globes in there -If it does a globe is causing it

willy
William Revit

Actually, thinking further about this,
I have seen a single element(single contact)
globe forced into a stop/tail hole doing the same thing by shorting the base terminals to each other
willy
William Revit

Gentlemen: thanks for your input. Unfortunately I have still not resolved the problem.

Lew Palmer:

This is not a recently rewired car. It actually has the original wire harness and original (or just very old, I think) turn signal relay. The original round tail lights (1953 TD) were replaced with Moss reproductions when the car was recently repainted.

The only change is that the car was stripped to bare metal and repainted a couple of years ago.

Rod:
I don't think a reversed cover is the problem because the relay has not been removed from the car in 28 years. Also it has not been re-wired.

William Revit:
When you say "globe" I assume that is what we call the light bulb. As you suggested, the first thing I did when I saw the problem was to remove the light bulbs in the tail lights, thinking they may have shorted from the brake light circuit to the side light circuit. This did no resolve the problem.

Thanks
Mark

Mark A. Sherman

When you say the front side lights turn on, are you speaking of the side light filament? Or is it the turn signal filament. One is brighter than the other.

The side/tail lights are completely independent of the turn signal circuit.

When you say it has not been retired, but it was repainted I assume you removed wires from lights to remove them? Did the problem occur when you reinstalled the lights?

Without a turn signal being activated the brake light signal passes thru the DB10 box directly to the rear lights using the relaxed contacts of the box.

In the front lights a lamp with dual filament but parallel tangs is used. Stop/tail is dual filament with offset tangs.

I would ensure tail/side lights work first, then move to brake lights next.

Only when they are working would I look at turn signals.

Peter
P G Gilvarry

Recently repainted- always suspect a bad ground. The relay box has to be grounded, as do the front wing lights. Try running a known ground wire to the relay box mounting/chassis, as well as the sidelight socket assembly. George
George Butz III

I agree. It possibly is a ground, even under the front fenders.

But I recommend a logical approach, ensure the side/tail lights work first, hence good grounds established. None of that goes through the relay box.

Then move to stop lights that go through the relay box with relays in relaxed mode, no ground required.

From memory there are a couple of ground at forward end of engine compartment using fender attachment bolts that convey ground to fender.

But having said all that, do the tail/side lights work? If yes, then move along.

Peter
P G Gilvarry

I suggest this is one of the problems that cannot be directly resolved via the bulletin board. The only way a solution can be found is to study the wiring diagram and methodically check everything. For example disconnecting the 22 terminal wire and connecting directly to the live terminal on the battery will show if the brake light switch is faulty - providing the internal relay contacts are clean and functioning! This applies to other issues such as engine miss fires. I strongly believe that to run a T Series car you need to be a competent automotive engineer or have a very deep wallet. Having said that please keep the posting problems and please let us know the eventual solution. There is nothing more frustrating that 23 post about an issue and nothing about how it was resolved!

Jan T
J Targosz

I am going to agree with the last sentiment.

However, these issues can be resolved by using a logical approach, testing one circuit at a time.

That is why I suggested checking the side/tail lights first, they are simple, don't involve anything but the switch at one end, ground at the other.

The brake light switch works, some lights he does not want come on when he presses the brake.

Over 50 years ago I was taught to take a logical approach to troubleshooting, that training has paid off in several cars, many wide bodied aircraft and home electrical systems.

I do suspect a ground/grounds due to recent paint job, but would like to know what he is actually seeing, is it a different filament that is lighting (turn signal) or actual side light.

Electrics are a mystery to many, sometimes it just needs a different approach.

My 2c worth.

Peter
P G Gilvarry

I didn’t read all the responses. The new DB-10 boxes supplied in the Moss wiring kits is electronic not breaker type as the original Lucas I tried several of the solid state repops when I had marker light issues flashing as four ways all the time or lighting up when brakes applied (separate issues at different times). This became evident when I swapped in LEDs in the tail lights. My car was also converted to negative earth as well but that wasn’t the issue. The three repop DB 10s I tried (all new) ended up having feedback issues between circuits that became more pronounce with the light current load of the LED tail lights. As to the markers lighting up when brakes where applied it appeared to be poor grounding at the 1130 marker lights.

The flashing signals occurred when the ignition switch was turned on. All wire connections where correct to the lights, flasher, relay box and turn switch. The problem was feedback with the relay box. I acquired several NOS Lucas breaker type relay boxes and switched the repop box for an original. Result was no more feedback to the 1130 markers and no flashing as four ways.

If you have a repop DB 10 check for residual feedback between circuits with a multimeter. If any is found replace the box with a serviceable breaker type DB 10

Bill Chasser
TD-4834
W A Chasser

In case it is useful, I had a recent problem, when I stepped on the brake, a rear position light went off. If the position lights were off, the brake light came on normally. Another Gremlin But since I do not believe in ghosts I investigated and discovered a bad ground connection to the braking light circuit. And now comes the good, the brake lights worked properly with the position lights off because they gave the connection to sufficient ground in these circumstances.
Gabriel Martínez

This thread was discussed between 06/05/2019 and 16/05/2019

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