rear fog lights

[jiffjaff]

hi i have a problem with no rear fogs and no tell tale light on the dash its not the abs fuse but there does not seem to be a fuse holder in the slot where it should be ......the bulbs are fine ...
does anyone have any ideas ???
thanks mark.

sorry its an 80 series vx auto 4.5 straight 6 cyl petrol/lpg on an n reg

 

[Justin_Elliott]

You'll have to trace back through the circuit to see where you lose power to the circuit.

Fuses are the obvious first check (Not quite sure what you mean by "there does not seem to be a fuse holder in the slot where it should be ") - Check all fuses to be sure.

Then eliminate all possibilities section by section (sorry if these seem obvious/basic, but its difficult to know what you have and haven't done), i.e.

Do the other lights work ok - is there any combined faults which need to be considered - remember the fog lights will only come on with the sidelights.
Check the switch operates (i.e. continuity changes when pressed)
Confirm there is no power to the circuit (at switch and rear fog lights)
Check the earth points near the dash.
Check continuity over each length of wire to see where the failure/break has occurred - it sounds like the fault will be close to the dash (as you say the light doesn't light come on with the dash switch).

iirc the wire's change colour as they go from section - section, which made the fault finding a little more challenging

I had the same problem and ended up replacing the majority of the wiring from the dash back to the lights. Its an easy find / fix when you know where to start. I've a copy of the Electical manual which was invaluable for this, but alas I don't have it to hand! (Currently in Montreal, Ca).

I'm sure someone else will chime in shortly to assist further...

Hope this helps.

 

[jiffjaff]

thanks Justin
all the other lights work fine there is power to the switch however the tester is the next point of call i was wondering if there were any more pointers before tracing wires ..... do you or anyone know if there is a relay near the switch ?
mark. also i have noticed a power drop on petrol its fine on lpg ... any ideas also is there any way of increasing the power on the truck ?
other people say i could get better mpg by tuning a little ????

 

[Justin_Elliott]

Re: Tuning - probably worth starting another thread. But imo yes the IP fuel pumps can go out of timing and therefore could be retuned.... but tbh its not something I'm particularily clued up on.

There is a relay in the drivers footwell behind the kick panel. Its in a group of 7 or so relays (if stock, it will be a round silver relay). You should hear this clicking in and out when you operate the switch.

It can be removed easily enough for checking that its receiving power / operating.

 

[Chris]

Check fuse 'ECU-B'

Chris

 

[jiffjaff]

hi Chris i have checked the ecu b fuse and all ok ..... any other ideas ??

 

[Chris]

Hmm. No. This is classically that fuse. Worth checking or replacing that fuse with another just to be sure. It's a very simple circuit and not much to check other than the lamps and the indicator in the dash.

Seen it several times and that fuse has always been the ticket.


Chris

 

[Ian Rubie]

This is going to sound odd but do you have a tow bar? If you do it could well be the cause of your problem. Some sockets have fog light cut out to stop the vehicle fog lights reflecting off the trailer. This goes wrong and you end up with no fog lights even if there are no trailer electrics plugged in.

Ian

 

[jiffjaff]

hello again and i just went and checked the fuse and replaced it with a new 15 a and still no joy ... do you know where the earth wires are for this circuit ? or where i can find the wires to start tracing them back ?
mark

 

[Chris]

They do indeed Ian. I actually though that was my problem from the start but it wasn't - in the end. But certainly worth looking at dodgy trailer socket.



Chris

 

[jiffjaff]

hello Ian i do have a tow hitch any ideas on how to check this out ?

 

[jiffjaff]

if the trailer socket is the problem would it stop the dash tell tail light as well ???
and any ideas witch wire colour it is in the socket ?
thanks for your help guys ! mark.

 

[Ian Rubie]

Blue wire.

Ian

 

[jiffjaff]

hi i have had a look at the rear socket and all seems to be mint inside however i did test and seems i have 12 v at the blue wire when the fog switch is on or off ??? after taking the blue wire out of the socket it made no difference any other ideas ?
mark.

 

[BobMurphy]

hi i have had a look at the rear socket and all seems to be mint inside however i did test and seems i have 12 v at the blue wire when the fog switch is on or off ???

Plug a trailer lighting board into the trailer socket and see if the trailer fog light works.

How is the trailer socket wired to the car?? If its spliced into the various looms you could have a problem where its joined.

Bob.