Hello,

New here but got an issue with my Focus already!

Its a Mk2.5 Titanium hatch.

Basically theres no reverse light working, I'm sure it was working when I got the car a fortnight ago but with the tints it's hard to tell!

The bulb is fine, and have even tried a new one to rule that out.

The bulb holder is getting 12 volts when in reverse so I assume the switch, fuse etc must be good.

The rear fog works fine.

I really can't understand why if the holder is getting 12 volts and the bulbs are working fine why the bulb in the holder doesn't illuminate!?

Would like to sort it asap really as there's no street lights in my village and that coupled with the factory tints are making parking on my drive in the evening difficult lol.

Cheers

Tom

Dirty/corroded contacts maybe? Give them a scrape with a flat bladed screwdriver etc

The contacts against the bulb are fine/clean.

Though I've been looking on here and found it could be corrosion between the plug and the bulb holder, so will check that tomorrow.

Perhaps the rear gear sensor on the gearbox

If the switch on the gearbox was the problem I don't think there would be 12 volts at the bulb holder?

I said perhaps, I had the issue on a chrysler minivan, but I'm clearly not the man of the situation.

I'm not really good at mechanics, just try to help.

Try a different bulb, although that one looks intact, did you measure it with an ohmeter?

Quick test to prove out the reverse switch on the gearbox - with car stationary put the wipers on then put the car in reverse. If the switch is OK the rear wiper will operate.

might be worth checking if there is 12v on it all the time or just when its in reverse?

an extension to that would be to check if there is 12v coming off the ground too.

a good example of 12v on 12v is the internal boot light for whatever reason mine turns off not by cutting the 12v line, but by pumping 12v down the ground. Didn't realise until I wired in a second boot light and grounded it off something else and it wouldn't turn off, had to run a second cable around to it to do the job

Anyhow, if its perhaps shorting out or damaged somewhere it might help explain it.

I really can't understand why if the holder is getting 12 volts and the bulbs are working fine why the bulb in the holder doesn't illuminate!?

This sounds like a high resistance somewhere in the circuit causing the voltage to collapse under load. Your test meter will have a quite high input resistance so won't load the circuit significantly.

Hmm, cant seem to multiquote for some reason so bear with me lol.

I did try another bulb yes, but also checked the original which had good continuity and about half an ohm resistance.

I've just tried the rear wiper trick....and it doesn't come on! So confused now lol, how can voltage get to the bulb holder if the switch is broken!? I do have a modified ELM with ELMconfig and FORSCAN, not got time to try it right now but would that be able to prove the switch is faulty?

Dee - I guess that's something to do with the CANBUS system? I didn't try testing it out of reverse tbf!

might be worth checking if there is 12v on it all the time or just when its in reverse?

an extension to that would be to check if there is 12v coming off the ground too.

a good example of 12v on 12v is the internal boot light for whatever reason mine turns off not by cutting the 12v line, but by pumping 12v down the ground. Didn't realise until I wired in a second boot light and grounded it off something else and it wouldn't turn off, had to run a second cable around to it to do the job

Anyhow, if its perhaps shorting out or damaged somewhere it might help explain it.

Could be that there is permanent 12v on one side of the bulb and the other terminal is grounded through the reverse switch.

Don't know for sure but it would account for what your seeing.

If this is the case then OP has a faulty reverse switch?

Looking at the wiring diagrams the lamp positive is fed from the PJB with a bit of canbus stuff going on, so it's not a case of a switched negative in this case.

Perhaps the switch isn't fully open circuit or there's partial damage to the wiring so you still get some voltage through to the bulb.

If the switch is reasonably accessible you could disconnect it then put a shorting link in the connector to simulate the switch operating, and see if the reverse light then comes on. That would prove out if it's the switch or a possible wiring issue.

Put a 9v battery, Positive to + side of bulb, neg to a body earth, see if bulb lights. That will test the negative side

Put a wire from negative bulb to body earth to test the positive side

At least that way you halve the wiring down

If the switch is reasonably accessible you could disconnect it then put a shorting link in the connector to simulate the switch operating, and see if the reverse light then comes on. That would prove out if it's the switch or a possible wiring issue.

This exactly what I've just done (turned out not as accessible as I expected lol), the bulb illuminates with a jumper wire so it is the switch at fault.

So I checked the bulb holder again....its getting 12 millivolts, not volts lol, I'll have to put my glasses on next time haha.

Glad you've found what the cause of the fault is.

If you're ever using your multimeter to check house electrics make sure you remember those glasses ;)

Wow this is an old post  probably had a few more cars by now. However . if there is anyone reading this , this may help! i need help too please.

take a wire with crock clips and clip to where you are getting 12v  + and -   Wish mine was   , then attach the other end to the bulb. ,, see if that work. If it does not then you have a duff bulb or its not sleeting right.

Anyone reading this I have no power going to the bulb holder. I have replaced the switch on the gear box.   Someone please tell me the right colour code. Checked all fuses. I am dum struck on this one. Ford focus 2004/5   zedec 1800 PJ05tFZ

I had the same problem on my focus Rs MK2 due to salt flicking up and causing hassle to the connection what I done I took the 12v socket that holds the bulb and tryed it on the fog light side and then tryed the fog lamp 12v socket on the other and that solved my problem as it come on so it’s obviously the 12v socket was corroded or just wasn’t getting the volts through.[emoji1360]


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