Indicator Earth Fault / Disco Lights

[james12345]

Hi. We have a '65 convertible, just through a new MOT which required some welding, and following my wife home when picking it up I noticed that there's a fault with the indicators.

With the side lights off, the indicators work fine. With the side lights on, the indicators give a nice disco light effect! I'm aware that this is an earthing fault, but for the life of me I can't find it.

Lights on, left indicator on - left indicator / left side light flash alternately.
Lights on, right indicator on - right indicator / left side light flash alternately.

I've tested continuity between the bulb body and the bolt on the boot catch, and the earth is good from all four rear bulbs. Starting to run out of ideas now!

With the flashing combination above, can anyone point me in the right direction of where to look next?? Rain has just stopped play for today, but I'dlike to get this fixed asap so the car can be used safely after dark. Could the welding have had an effect? I've no idea if the issue existed beforehand though.

[mogbob]

Which part of the car was the welding done on ? A good welder would have isolated the battery before welding.

Any way if you car hasn't been " mucked about " with electrically, the side lights and the indicators are on separate circuits.So it is an unusual problem.
Could you clarify a little further please... are the sidelights on each side, back and front re-acting in the way you describe ?
It would help the Forum isolate the problem for you.

Bob

[james12345]

Hi Bob.

The front indicators / sidelights are all behaving as expected - only the rears are affected.

The welding was carried out by a reputable Minor specialist, and the welding was to the floor / chassis around the rear hanger on the passenger side.

I'm convinced it's an earth fault somewhere, but I'm lost as to where it might be!

[mike.perry]

What happens when you operate the stop lights whilst indicating? What about the number plate light? I suspect an earth problem within the light units.
Also check the wiring loom between the o/s and n/s rear lights

[james12345]

Hitting the brakes seems to stop it all flashing all over the place, and seems to give normal operation.

Could that mean a faulty unit? I'm not averse to buying new ones as the existing ones are slightly pitted, but I'd prefer to fix rather than swap.

[mogbob]

As Mike has suggested....check the wires from the offside to nearside ....they lie on the horizontal floor at the rear edge of the boot area i.e right above where the welding was done.
I'll wager 50 p that the wires are melted along that run and that the power is going to earth through to which ever takes it's fancy alternately.
If this is the case I'd go back to the garage and asked them to repair the short lengths of wire.
Bob

[james12345]

I've already been through the wires where they cross the boot floor - nothing untoward there. However, melting could well be the problem, especially if it's where the wires pass through the bodywork. I'll have to have a closer inspection there, I think! Sounds very likely that something there is shorting out causing the fancy disco effect. Many thanks for all of the replies

[mike.perry]

If they have been disconnected make sure that they have been correctly re connected

[bmcecosse]

It IS an earth fault - on one of the LH light units. You say there is a good earth path to the boot catch - but have you checked the front light unit for a good earth??

[james12345]

I checked that the earth points on the front lights were good (battery negative to the earthing bolt), but not from the bulb holders themselves - will look there as well.

Also, I don't believe that the rear lights were disconnected, but will double check. That said, the lights all light correctly when used separately but play up when sides and indicators are on - which definitely points to an earthing problem. My issue is finding where the bad earth actually is!

[bmcecosse]

You are on the right track - just keep going.......