Headlight fault - any ideas??
Discussion
I experienced my first electrical gremlin in EIGHT YEARS on my 4.5 last night.
The lights (side, dip and tail) have stopped working. It's not the fuse. It's not the control box that sits to the left of the CD jukebox with the indicator controller either (checked that in another Cerbera).
The fault:
I can't get side/dip/tail at all - or rear fog. (I have main beam, brake, indicators etc.)
When I switch on the ignition, the mainbeam flash works as it should - i.e. main beam on for as long as I press the switch.
If I then turn on the lights, the main beam button now latches when I touch it - i.e. main beam on until I press again to unlatch.
If I now turn off the light switch, the main beam button then only latches (ie the light switch going to the 'on' position causes the function of the main beam button to go from momentatry to latch ...and then stay that way).
If I turn off the ignition then on again, the main beam button 'resets' to being on-while-pressed.
From this I deduce the fuse is OK, the light switch is OK ...but there is something else somewhere that isn't. What is it?
The lights (side, dip and tail) have stopped working. It's not the fuse. It's not the control box that sits to the left of the CD jukebox with the indicator controller either (checked that in another Cerbera).
The fault:
I can't get side/dip/tail at all - or rear fog. (I have main beam, brake, indicators etc.)
When I switch on the ignition, the mainbeam flash works as it should - i.e. main beam on for as long as I press the switch.
If I then turn on the lights, the main beam button now latches when I touch it - i.e. main beam on until I press again to unlatch.
If I now turn off the light switch, the main beam button then only latches (ie the light switch going to the 'on' position causes the function of the main beam button to go from momentatry to latch ...and then stay that way).
If I turn off the ignition then on again, the main beam button 'resets' to being on-while-pressed.
From this I deduce the fuse is OK, the light switch is OK ...but there is something else somewhere that isn't. What is it?
So control box works in the other cerb, the bulbs are ok, the fuse is ok, the switch is ok.
The only thing I can think of is maybe some wiring is shorting somewhere? or maybe theres a power issue? Try hooking up a multimeter to the main power terminals on the control box, and get the other half to go through the light switch motions and monitor the power fluctuations, if there is a short or power issues, should show up by a sudden drop and rise on the inputs of the control box which could affect the control box's operation, whence why its running fine in the other cerb.
Thats what I'd do next, before ripping out the wiring loom and then tracing the whole damn thing from end to end.
The only thing I can think of is maybe some wiring is shorting somewhere? or maybe theres a power issue? Try hooking up a multimeter to the main power terminals on the control box, and get the other half to go through the light switch motions and monitor the power fluctuations, if there is a short or power issues, should show up by a sudden drop and rise on the inputs of the control box which could affect the control box's operation, whence why its running fine in the other cerb.
Thats what I'd do next, before ripping out the wiring loom and then tracing the whole damn thing from end to end.
I was gonna sugest the dim/dip control box might have something to do with it, but on re-reading your post I'd say not.
So it sounds like an earth (or negative as it is in the Cerb). I'd check every light cluster, check for continuity on the common connection (i.e. the negative) to every lamp.
If one cluster's negative connection has gone open circuit or high resistance then the system will be getting its negative via another lamp and all sorts of wierdies will happen. You know the way on normal cars you sometimes see brake lights flashing instead of indicators?
And of course check the control box is getting a nice clean + and - supply. Locate its +ve and -ve supplies on the connector, then measure them directly to the battery - i.e. measure between the -ve at the plug and the +ve at the batt and between the +ve at the plug and the -ve at the batt. You should get the same voltage each time.
I'd bet some connection has fallen off or corroded somewhere.
Hope that helps.
Andy.
So it sounds like an earth (or negative as it is in the Cerb). I'd check every light cluster, check for continuity on the common connection (i.e. the negative) to every lamp.
If one cluster's negative connection has gone open circuit or high resistance then the system will be getting its negative via another lamp and all sorts of wierdies will happen. You know the way on normal cars you sometimes see brake lights flashing instead of indicators?
And of course check the control box is getting a nice clean + and - supply. Locate its +ve and -ve supplies on the connector, then measure them directly to the battery - i.e. measure between the -ve at the plug and the +ve at the batt and between the +ve at the plug and the -ve at the batt. You should get the same voltage each time.
I'd bet some connection has fallen off or corroded somewhere.
Hope that helps.
Andy.
Check ALL the fuses, Cerbs have a wierd electrical system. On most cars if a fuse goes, something STOPS working, on Cerbs if a fuse goes, other things START working when they shouldnt.
I blew the fuse in the cig lighter once (didnt know at the time) and the main beam, 4 way flashers and wipers all came on when I put the ignition on. Spent ages trying to check all the wiring under the steering coloumn, and finally checked the fuses. The fuse which had blown was nothing to do with any of the above, but when I replaced it, everything went back to normal.
I blew the fuse in the cig lighter once (didnt know at the time) and the main beam, 4 way flashers and wipers all came on when I put the ignition on. Spent ages trying to check all the wiring under the steering coloumn, and finally checked the fuses. The fuse which had blown was nothing to do with any of the above, but when I replaced it, everything went back to normal.
jensena said:
Check ALL the fuses, Cerbs have a wierd electrical system. On most cars if a fuse goes, something STOPS working, on Cerbs if a fuse goes, other things START working when they shouldnt.
I blew the fuse in the cig lighter once (didnt know at the time) and the main beam, 4 way flashers and wipers all came on when I put the ignition on. Spent ages trying to check all the wiring under the steering coloumn, and finally checked the fuses. The fuse which had blown was nothing to do with any of the above, but when I replaced it, everything went back to normal.
Would agree with that! I had rear fog stop the other day - the rear fog fuse (same as side!) had NOT blown...very confusing for a while. Was a completely different fuse. I was putting in new rear lights so it wasnt unexpected to have a glitch or two.
I also had the rotary switch break on me, main beam still worked - but did not latch like you seem to be able to do. Worth thinking about though, they do break, it could just be on its way...
Thanks for the suggestions. 
I tried all fuses when it failed ....on the Midnight Tunnel Run
Nice...
The problem started when someone noticed the n/s rear bulb (tail and brake) was out. I tried wiggling the bulb with the lights switched on, to no avail. Switched lights off. Then switched lights on and ....nothing. [I've since replaced that bulb and got both brake lights back.]
I think the bulb wiggling fried a relay/control box somewhere. The switch behaviour I described in my first post suggests a relay/transistor somewhere can latch to enable main beam to work, but not the general light cicruit.
I'm one Cerbera down at home at the moment - when the other one's back I'll try swapping another light control box that sits to the right of the CD jukebox.
I tried all fuses when it failed ....on the Midnight Tunnel Run
Nice... The problem started when someone noticed the n/s rear bulb (tail and brake) was out. I tried wiggling the bulb with the lights switched on, to no avail. Switched lights off. Then switched lights on and ....nothing. [I've since replaced that bulb and got both brake lights back.]
I think the bulb wiggling fried a relay/control box somewhere. The switch behaviour I described in my first post suggests a relay/transistor somewhere can latch to enable main beam to work, but not the general light cicruit.
I'm one Cerbera down at home at the moment - when the other one's back I'll try swapping another light control box that sits to the right of the CD jukebox.
BossCerbera said:
Thanks for the suggestions.
I tried all fuses when it failed ...
...well, not all, or not ALL THOROUGHLY.
Turned out to be a fuse (No2, 15A). The fuse I changed was No4, 20A (dip headlight and dim/dip), No2 is sidelights and rear fog. Perfectly logical.
So - really - the old girl continues to be an electrical gremlin-free Cerbera. Fuse blow was caused by me wiggling a failed bulb.
BossCerbera said:
Thanks for the suggestions.
I tried all fuses when it failed ...
...well, not all, or not ALL THOROUGHLY.
The fuse I changed was No4, 20A (dip headlight and dim/dip), No2 is sidelights and rear fog. Perfectly logical.
So - really - the old girl continues to be an electrical gremlin-free Cerbera. Fuse blow was caused by me wiggling a failed bulb.
lol, happens to the best... also make sure whenever you fit bulbs, you clear any thumbprints off, heat reflection causes the bulbs lifespan to decrease immensly...
Gassing Station | Cerbera | Top of Page | What's New | My Stuff