Took the car to the MOT station and one of the things it failed on was fog lights, further investigation and popping fuses like sweets! Rears work fine until the front are plugged in. bulbs are both ok and terminals read about 0.2 - 0.3ohm, checked the wiring from the lighting twist connector (slam panel) to the terminal plugs and all seems ok, checked ground from terminal plug to battery and one was 0.0ohm but other was slightly higher at 11.1ohm (wondering if there is a bad earth here causing the issue) with them unplugged and switch turned on I am getting about 11.99v (ignition only not running) so power is getting there. left them unplugged for now as not needed for the MOT but thought I would see if any one has any suggestions other than that ground being higher at 11ohm? Also annoying the Haynes hasn’t got the wiring diagram for the front fogs and oddly each terminal plug has its on ground back to the twist connector at the slam panel so assuming they have seperate earth back to the main earth terminal by the steering column?!?
there are 2 earths in the slam wiring yep, all the earths for the lamps either side tap together near the light and then run back to the wires at the round plug. since it only blows when the fog lamps are plugged in this suggests faulty lamps to me, try 1 lamp plugged in at a time see if you can narrow it down to a particular side. doesnt seem like a wire short since if the bulbs are unplugged it should still blow...
Hi Jonny thanks for the reply, I have tried everything that’s what is throwing me out, just tried both lamps in each side and they both work on each side but I didn’t put them both back in together as I only had 1 15 amp fuse left and I needed to take it for it’s retest. Makes me think it’s a load issue but rear bulb is drawings like 1.7amp and the fronts are 55w bulbs so should only be drawings 9.1amp so say 11amp collectively. I will have another look at it once I get it home but when I put my meter on it last time(15amp max) it was over that and was bleeping unhappily at me lol
The wiring circuit isn't all that complex, a 12v feed using grey-yellow wire arrives from the switch at the front panel connector, and then continues to each lamp. There should be battery live voltage on this Grey-yellow wire at each lamp connector with the ignition and the lamps switched On. Each lamp is earthed separately, but I doubt the wires run back into the cabin. They're more likely to use the earthing points under the battery platform. I'd disconnect the multi-pin front panel connector, and use the meter on ohm setting to check between the pin with the Grey-yellow fog lamp wire(s) and one of the earth wires, i.e. simply through the lamp itself. It should show the resistance value of a 55w bulb. The other circuit should be similar. Going by Voltage = Current x Resistance, if the current drawn by a 55w bulb is 4.58 Amps, the resistance works out as around 2.6 Ohms.
