Fog Lights

[shade82000]

Hi all, got a question about the front fogs on our 172 mk2 ph1.
They haven't worked since we bought the car last year but one of them got a broken lens so I bought a used one from ebay and fitted it today thinking it would be easy to fix ... still not working though.
The rear light works fine and the dash indicator comes on for front and rear when I turn the stalk round.
I've had the multimeter on it today and everything seems like it should work. There is 11.2v on the two spade connectors inside both light units when both of them are unplugged, but if I connect one back up the voltage drops to 0v on the other one. I think this means that the voltage is being grounded through the bulb that is connected but they are not coming on.
Both bulbs look like they should work, the filaments are fine and the multimeter bleeps when I do a continuity test.
Is there something else that I should be checking? I thought it would be a simple battery-switch-bulb circuit but I'm probably missing something.

Thanks!

 

[RenMatt]

Hi well the last one I had with that problem turned out to be the switch ., when looking at the switch off one of the small wires had broken ,Also worth checking for corrosion were the fog light wiring plugs in behind the pas front wheel arch liner , good luck

 

[shade82000]

Cheers for that. I will check the switch and earth but there is a voltage going to both bulb connectors when the stalk switch is on so it should be ok. Might try some new bulbs anyway.

Thanks.

 

[shade82000]

Man this is confusing me now.
Got some new bulbs a few weeks ago but that didn't fix it.
I had some more time to play with it today - took the wheel off to get to the wiring and noticed it disappears into the loom just to the right of the battery, inside a triangular fuse box. It doesn't appear to connect to the bodywork anywhere.
So I got a couple of 12v LEDs and connected them instead of the bulbs. Yes they work so it must be the bulbs right.
Nope, the bulbs work fine when I connect them straight to the battery.
Then I put the bulbs back in their sockets and connected the multimeter in line with one of the terminal. It shows the right voltage when the lights are turned on showing that there is a circuit through the bulbs.

So we have good bulbs, 11.2v at the connectors when the switch is on, 0v when it's off, the relay clicks on / off and LEDs work on the connectors but the bulbs don't work in their sockets.

As above, really confused.