Fog lamp not working - help?

Chris152 · Jun 3rd, 2024, 09:37

1990 240 GLT - we've changed the bulb and fuse seems to be fine. So we just checked the Volts to the switch and it measures 32V, but 0 Amps. I don't understand! It also didn't light the bulb as in the pic (but with ignition on).

Couple of questions:

1. How could I get that measurement? I guess I'm doing something wrong, I'm still not used to a multimeter.
2. If the switch is working, is our next stop the relay? Oh, and
3. Which side is the fog light supposed to be on - driver's or passenger's? It's RHD in the UK.

Thanks for any thoughts, Chris

loki_the_glt · Jun 3rd, 2024, 20:13

At that age the rear fog lights are wired through the headlights - if you have either dip or main beam selected the rear fog lights should come on; only the early (pre-1981) cars had their rear fog lights wired to come on in ANY lighting configuration. Try the switch again but with the headlamps on as the first port of call.

There are two on both saloon and estate models - the estate ones are at the top of the cluster, while the saloon ones are in one of two positions and the changeover was around 1990!

Chris152 · Jun 4th, 2024, 07:43

Thanks Loki - we didn't know that! However, it's still not working - but, we now have a reading of 3A and just shy of 11V at the fog switch contacts.

Checking continuity of the unplugged switch contacts on and off, the meter registered 50+ Ohms in the On position. Does that tell us anything?

Thanks, Chris

ps Loki - do you recognise the leads and bulb?! Still going strong :-)

Chris152 · Jun 4th, 2024, 08:32

Update - the resistance on the switch was being caused by corrosion - I opened the switch and cleaned the contacts and - Hey presto, the fog lights are working!

We've finally managed to use the multimeter to figure out and resolve a problem :-)

Jun 3rd, 2024, 20:13	#2
loki_the_glt Torquemeister Last Online: Yesterday 16:18 Join Date: Dec 2004 Location: Asgard, Cheshire	At that age the rear fog lights are wired through the headlights - if you have either dip or main beam selected the rear fog lights should come on; only the early (pre-1981) cars had their rear fog lights wired to come on in ANY lighting configuration. Try the switch again but with the headlamps on as the first port of call. There are two on both saloon and estate models - the estate ones are at the top of the cluster, while the saloon ones are in one of two positions and the changeover was around 1990! __________________ loki_the_glt - Skipper of the Exxon Valdez, driver of Sweden's finest sporting saloon - and pining for another Slant-4.

Jun 4th, 2024, 07:43	#3
Chris152 Senior Member Last Online: Jun 4th, 2024 10:02 Join Date: Jan 2020 Location: Cardiff	Thanks Loki - we didn't know that! However, it's still not working - but, we now have a reading of 3A and just shy of 11V at the fog switch contacts. Checking continuity of the unplugged switch contacts on and off, the meter registered 50+ Ohms in the On position. Does that tell us anything? Thanks, Chris ps Loki - do you recognise the leads and bulb?! Still going strong :-) Last edited by Chris152; Jun 4th, 2024 at 07:55.

Jun 4th, 2024, 08:32	#4
Chris152 Senior Member Last Online: Jun 4th, 2024 10:02 Join Date: Jan 2020 Location: Cardiff	Update - the resistance on the switch was being caused by corrosion - I opened the switch and cleaned the contacts and - Hey presto, the fog lights are working! We've finally managed to use the multimeter to figure out and resolve a problem :-) Last edited by Chris152; Jun 4th, 2024 at 08:34.

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