Failed MoT on rear light issue - where's the earth point?

[Joseph Martin]

My 1988 360 GLE failed its first MoT in two years - two very minor issues.

With the headlights on, pressing the brake turns off the bulb completely on the right hand side. I'm thinking this is down to a bad earth. Where are the rear lights unearthed to, or am I looking in the wrong place?

Any advice appreciated.

[Baxlin]

Rather than try finding the original earth, could you take a new one from the offending light, to at least test your theory?

[Joseph Martin]

Originally Posted by Baxlin

Rather than try finding the original earth, could you take a new one from the offending light, to at least test your theory?

I could attempt to, I will be honest in that electrics are not my strong point at all, I'm more mechanically-minded. But I shall try to see what I can do.

[john.wigley]

Might it just be a dodgy bulb, Joseph? Worth substituting it with a known good (new) one to eliminate it before delving deeper? I've had bulbs that appeared sound playing silly b's with me in the past ...

Regards, John.

[Laird Scooby]

If memory serves, the 360 rear lights have a crude multiplug to connect the loom to the clusters, very much like the Fords of the time.

The fault sounds very much like a bad earth on the stop/tail bulb, could just be the bayonet of the bulb is corroded and needs cleaning or the bulbholder itself or if my memory is correct about the multiplug, the contacts in that and on the cluster - clean them with a soft wire brush, emery cloth or similar but not sandpaper. Once clean and normal service is resumed, disconnect the multiplug from the cluster, smear silicone grease on the contacts of both and reconnect with a final test. The silicone grease will exclude more moisture from corroding the contacts again.

[Joe Harding]

The galvanised strip in those lights is pretty crude as well. As above, a good clean, contact cleaner spray and don't forget to emery the bulb contacts too and it should be fine. They are prone to water ingress too. Our rear lights have a tiny hole drilled in the external surface to allow rainwater to drain out, otherwise the light is filtered through a pool of water.

[Clan]

Originally Posted by Joseph Martin

My 1988 360 GLE failed its first MoT in two years - two very minor issues.

With the headlights on, pressing the brake turns off the bulb completely on the right hand side. I'm thinking this is down to a bad earth. Where are the rear lights unearthed to, or am I looking in the wrong place?

Any advice appreciated.

On the back of the plastic housing where the bulb holders are is a thin metal bar which runs long and presses on each bulbs case , the bar has a earth wire on it , as you only get a problem with one bulb I would take the bulb out and clean its casing and look carefully at the strip which it presses up against.. sometimes the plastic support holding the strip can break .. can be fixed with a strong epoxy glue to strengthen the strips support..

Or it may just be a dirty bulb and case contact .

[Joseph Martin]

FIXED!

As per Clan's suggestion, the bulb wasn't properly engaging with this metal bar, and I've now confirmed this and it works.

Will be going for retest on Monday. And with these faults sorted it'll then have a totally clean bill of health.

Not bad for a 33 year old Volvo 300 series!

Thanks again for all your advice!!

[Two340'sman]

Years ago I had similar problems, soldered separate earth wires to each bulb holder, no further trouble.

[Joe Harding]

I just empty a couple of sacks of fertile loam in the boot. Ensures good earthing all round.