Help please! - Failed MOT and I cant seem to fix it!

[Thatch]

P&J failed its MOT due to the front side (parking) lights not working. I have tried everything i can, but i cant find the problem!

Situation:
- both front side lamps wont work (but the garage has checked the bulbs and said they are fine)
- rears do work
- have the dashboard out and checked the connections to the switch
- checked the switch itself - working fine
- transferred all the connections to a spare switch i have - same symptoms!
- pulled out and refitted every fuse and relay in the footwell
- checked the electrical connectors in the panel behind the passengers door

and still no front lights.

tried to follow the cables from the back of the dashboard switch, but they soon go into the loom, so cant get very far at all.

This is killing me!

Any ideas?
Anyone!

[BliarOut]

Do you get 12V on the spade connector down by the sidelights?

Is the earth wire good? (measure resistance to ground)

Have you put a multimeter across each fuse? (my horn isn't on the fuse it should be on!)

[Guillotine]

probably the earth.

check volts at the lamp holders.
To lamp casing, then to a known earth.

[Thatch]

looks like i will have to get to the bulbs myself then (assumed that they would be OK because the garage checked the bulbs)

where are the bulbs earthed?

[V8Bart]

There are a couple of common ground points on the chassis, weather gets to them. Can sort just by un bolting and using wire wool or wet and dry then rub with a dab of oil or wd40.

[Thatch]

V8Bart said:

There are a couple of common ground points on the chassis, weather gets to them. Can sort just by un bolting and using wire wool or wet and dry then rub with a dab of oil or wd40.

Can you give me directions?

[steve-V8s]

There is an earth point to the end of one of the chassis rails, drivers side I think. To get at it sensibly you need to lift the radiator up a bit.

However I suggest the first thing to do is get access to at least one of the bulbs. Take the bulb out and with a multimeter switched to ohms check across the bulb. If it is OK you should measure just a few ohms if the bulb is good. Switch the meter to DC volts connect the black probe to something earthed (the engine will do). With the red probe measure to both sides of the bulb holder and see if you have 12v on one of the terminals with the lights switched on. If you get 12v switch the lights off and check it is no longer there to prove you are measuring what you think you are. If no 12v then go back to the switch and start checking from that end. If you do have 12v put the bulb back in and connect a wire from the other terminal ( the one that didn’t have 12v on it and something earthed and switch on again. If the bulb lights it is the earth connection which is probably common for both lights. If it doesn’t light then it is the bulb holder.

[Guillotine]

since the other lights are working at the front, the earth to the chassis should be ok.
just run a good earth to the lamp casing. Much easier than getting to the front earth bolt.
again, make sure you have 12v.

[Thatch]

steve-V8s said:

There is an earth point to the end of one of the chassis rails, drivers side I think. To get at it sensibly you need to lift the radiator up a bit.

However I suggest the first thing to do is get access to at least one of the bulbs. Take the bulb out and with a multimeter switched to ohms check across the bulb. If it is OK you should measure just a few ohms if the bulb is good. Switch the meter to DC volts connect the black probe to something earthed (the engine will do). With the red probe measure to both sides of the bulb holder and see if you have 12v on one of the terminals with the lights switched on. If you get 12v switch the lights off and check it is no longer there to prove you are measuring what you think you are. If no 12v then go back to the switch and start checking from that end. If you do have 12v put the bulb back in and connect a wire from the other terminal ( the one that didn’t have 12v on it and something earthed and switch on again. If the bulb lights it is the earth connection which is probably common for both lights. If it doesn’t light then it is the bulb holder.

Accessed one bulb, it is OK (continuity across the filament)

cant see 12 v at the bulb holder with switch on :-(

but i cant for the life of me see anything wrong behind the dash before it goes into the loom.


this is incredibly frustrating.


Do you think i can somehow piggy back off the live going to the main beam? otherwise i am going to have to wire a new positive to the side lights, and i don't fancy that!

[Simon says]

What car is it ?

[Thatch]

Simon says said:

What car is it ?

1992 4.0 litre, converted to 4.3BV in 2002

[jagracer]

Thatch said:

Do you think i can somehow piggy back off the live going to the main beam? otherwise i am going to have to wire a new positive to the side lights, and i don't fancy that!

No because the side lights have to work independently of the headlights. How much hassle would it be to run a wire to the side lights from the switch just for the MOT?

[davep]

I had something similar when I changed my dash. The problem was a high current drain occurring in the dash illumination cct's when the side lights were switched on. I traced the problem to the clock bulb feed and socket, which for some reason was making a partial short. So perhaps a quick check on the instrument bulb 12V feeds might cure the problem as both cct's (dash and side lights) use the same switch. Also, on my car (pre-cat) there is a 'spare' 12V lead in the vicinity of the clock, you could try swapping the bulb feeds around and see what happens.

[Thatch]

jagracer said:

No because the side lights have to work independently of the headlights. How much hassle would it be to run a wire to the side lights from the switch just for the MOT?

Like your thinking, but i dont fancy having to go through the bulk head and drilling from the engine compartment through to the inner wing!!!

[Thatch]

davep said:

I had something similar when I changed my dash. The problem was a high current drain occurring in the dash illumination cct's when the side lights were switched on. I traced the problem to the clock bulb feed and socket, which for some reason was making a partial short. So perhaps a quick check on the instrument bulb 12V feeds might cure the problem as both cct's (dash and side lights) use the same switch. Also, on my car (pre-cat) there is a 'spare' 12V lead in the vicinity of the clock, you could try swapping the bulb feeds around and see what happens.

sounds interesting.

PS what's a "CCT"?

[davep]

Thatch said:

sounds interesting.

PS what's a "CCT"?

Abbreviation for circuit.

Did your front side lights work prior to the dash and alternator problems?

A quick check to eliminate the dash circuit as the cause would be to disconnect its 12V feed from the side light switch.

The 'bible' circuit diagram shows the double Red/White 12V feed circuits from the side light switch go to:

- rear side lights
- front side lights
- lights in the window switches
- lights in the heater control switches
- cigar lighter lamp.

The double Red feed from the side light switch is used for dash illumination.

If all lamps bar both the front sides are On with the switch On, establish that there really is a continuity problem in the common feed to both front lights by swapping the two double Red/Whites on the switch.

Edited by davep on Sunday 8th May 20:58

Edited by davep on Monday 9th May 09:38

[Thatch]

Thanks Dave for the pointers. Another couple of frustrating hours and still no joy. :-(

to answer your questions above:
-all the dash illuminations work well
- the cigar lighter light works
- there are two live 12v feeds going into the dash switch
- all connections look fine

tried all combination on the switch, and still the same symptom - front parking lights only wont work.

(In answer to your other questions in this and other threads, yes i had this problem before the alternator change, and I only noticed the problem after I refitted my repaired speedo about 3 months ago)

All i can think of now is trying to wire a new front light feed through the bulk head and down the inside of the wings, but i have no idea how difficult (if at all possible) this will be!

I wish i knew where the front and rear feeds split, as it obviously there where the problem occurs.

Thanks for everyones help and support.

[davep]

Damn! Following the Red/White leads to the loom multi-connector(s) is there 12V on the main loom side?

Removing the dashboard surround gives access to the thick end of the loom, see here:

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

I'm not sure, but I think the front lighting loom is routed through the nearside inner wing void. However, when working on a heater/blower fix on my car I found an access hole to this void in the nearside inner wall of the passenger footwell, and there is a wiring loom in there. I'm guessing the hole was cut to allow access to the void without having to remove the dashboard surround and heater matrix. This might be an option for a 'quick fix' route.

[Hedgehopper]

There is a cover plate under the AFM, did ask why it was there but had no answers so guess it might be for the wiring harness.



There are also several connectors under the headlamp pod, probably accessible by removing cover plate at back of headlamp.

Good luck

[leerdam23]

Just out of interest, have you tried switching the dash lights off with the switch under the steering column?

Also, have you tried a continuity test from the fuse to the bulb holder?