J

jase750

Active Member
OK I give up, my rear fogs don't work an MOT fail too.
The fuse is ok and if I bridge out the switch the rear lights come on and the tell tail light on the switch works too.
Its the non latch type of switch I can't hear any relays in the passengers foot well clicking and I've swapped no 1 and 5 relays just to try and still nothing.
Any ideas folks?
 
jase750 said:
OK I give up, my rear fogs don't work an MOT fail too.
The fuse is ok and if I bridge out the switch the rear lights come on and the tell tail light on the switch works too.
Its the non latch type of switch I can't hear any relays in the passengers foot well clicking and I've swapped no 1 and 5 relays just to try and still nothing.
Any ideas folks?
Click to expand...

I thought D1 fog lamp switches were all latching (certainly my 300 has all latching switches) - only D2 uses the BCU and non latching switches? If so I suspect your switch is the culprit.
 
The d1 switches are non latching, they go off when you turn the lights off. They are controlled by the mfu on the back of the fuse box.
Try holding the switch in for 5 or so seconds with ignition and headlights on, that's how I found mine work. Has to be a loooong press, not just a quick press.
 
i wouldnt think its the mfu i'd be looking at getting a known working switch and try that first after all the lights do work when you bridge the switch you have now..
 
quattro6999 said:
The d1 switches are non latching, they go off when you turn the lights off. They are controlled by the mfu on the back of the fuse box.
Click to expand...

Thanks for that - thought the non latching stuff came in with the D2! Learn something every day - thanks :tea:
 
OK swapped the fuse board and mfu and now everything that wasn't working.
Interior lights,
Rear wiper,
Rear wash,
Heated rear screen,
Intermittent wipers.
All work perfectly everything but the bloody fog lights?????
 
jase750 said:
OK swapped the fuse board and mfu and now everything that wasn't working.
Interior lights,
Rear wiper,
Rear wash,
Heated rear screen,
Intermittent wipers.
All work perfectly everything but the bloody fog lights?????
Click to expand...

Put the MFU through the diagnostic test, it doesn't depend on any switches being operated so if the fog-lamps illuminate in the test u know the MFU is ok.
 
Tried it a couple of times.
Hold the heated rear screen button,
Turn on the ignition,
Release the button.
I don't get a beep ?
 
Are the headlights and ignition on when you are trying them? May seem silly, but I think they only work when both are on
 
So even that your MFU failed the diagnostic test u still believe its ok, have you checked the feed back to the MFU and do u have a trailer socket that may be putting a short on the feed?
 
Last edited:
It has got towbar electrics on so I might disconnect them and see if that m,akes a difference.
It's just strange that everything else works bar the fog lights??
I may have to admit defeat and call a proffesional auto electrician
 
Just see if u 12v in the o/s rear light cluster at the position of the bulb when the dash fog s are switched on there is just a single wire to look at. There's a circuit diagram in the Haynes book
 
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