Intermittent electrical fault...

[xvivalve]

Took a Sprint for an MoT yesterday and discovered that the neither the rear lights and number plate illumination to be working. Came home to investigate, and without touching them, suddenly they were working. Probably something lose somewhere; any suggestions as to where it might be given it affects both sets of lights?

Indicators, hazards and reversing lamps all function correctly.

MoT exempt and not that I drive it at night, I take comfort from getting an MoT pass each year

[soe8m]

You could check the connector of the rear harness where it connects at the main harness.

A few weeks ago on a customers Dolomite it was corrosion on single pins what caused similar problems. It had intermittent main beams and the wipers sometimes wouldn't park. The connectors under the steering column had some pins corroded. Don't ask why but that car had just some single pins corroded in a connector. The others around in the same connector were fine and hadn't any trouble.

You probably did check it wasn't a former dimmer relay car and the bodge isn't holding anymore..

Jeroen

[xvivalve]

That seems logical, but I was hoping for a different suggestion; I don’t think the parcel shelf has ever been removed in this car before

When they do work, they’re really bright, which surprised me; I thought they’d dim with bad connection or earth…

[new to this]

Have you checked the rear lamp holders

[xvivalve]

Have you checked the rear lamp holders

No, because it would be great co-incidence for both tail lights and both number plate lights to chose not to operate at the same time, every time , were it a bad connection between individual bulb holders and earth.

[MIG Wielder]

That seems logical, but I was hoping for a different suggestion; I don’t think the parcel shelf has ever been removed in this car before

When they do work, they’re really bright, which surprised me; I thought they’d dim with bad connection or earth…

Hi Alun, I reckon you have 2 faults.
1. The intermittency on the red wire.
2. The overbright bulbs at the back.

For 2. I think that either they are the wrong bulbs, or that one of the brake light filaments has drooped and is now touching the rear light filament.
For a test, with the rear lights in their bright state, press the brake pedal with the Ignition OFF.
If the IGN light comes on then the cause is either a drooping filament or a short circuit between the brake light and rear light circuits.
I see it is an early car (M ?) so it may have the light dimming relay. Is this the case with the car please ?

I'll come back to you on problem 1.

HTH,
Tony.

[xvivalve]

Hi Tony,

When I said 'really bright', I didn't mean brake light bright, just brighter than I'm used to seeing with a 50 year old loom! The brake lights still operate brighter yet than the bright side lights.

[soe8m]

There's only one connector that has the fronts and the rears connected so when the fronts do, it's that connector. I believe the night dimming relay has a double wire crimped in one spade so that would be a take off only.

You could check your towbar wiring. Sometimes it's taken off before the dimming relay and sometimes that's connected very creative.

Jeroen

[TrustNo1]

I'd be looking at the towbar wiring first