Reverse light not working

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richardjeaton

richardjeaton

New Member
Posts
198
Location
Wetherby, Leeds, West Yorkshire
I noticed last week that my reverse light had stopped working and assumed it just needed adjusting as that is all it needed last year when the same thing happened - but no... :doh:

I tried adjusting the switch and it made no difference so I went back to basics and checked the bulb. Bulb was fine and I checked with a multimeter and no 12v to the bulb holder.

So I went back to the switch and disconnected the 2 terminals. I assumed that one would be 12v and the other is a return which the switch will allow 12v to flow to if in reverse. Again the multimeter (with one side grounded) showed nothing on either wire :mad:

Any ideas???

I wouldn't normally be that bothered but when I reverse down my lane to park I can't see bob all and nearly wiped out the hedge earlier :eek: I was already thinking of fitting a rear spot light connected to the reverse lights (via a relay of course!) because of this but there's no point connecting it to something that doesn't work :rolleyes:
 
trace the wires (green and green with black stripe iirc) to near the clutch and brake master cylinders (check wires haven't chafed through anywhere) to see where they plug into connector blocks and clean and test .
 
short wires on reversing light switch failing that behind rear lights the loom chaffs through
 
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Had a similar problem with my reversing light. Checked bulb - fine. Checked earth for bulb - fine.

Located reversing switch on top of gearbox and it was not connected. Found the relevant wires dangling somewhere and connected them.

Now we have 12V at the bulb! But whenever we actually connect the bulb the p.d drops to near zero.

Checked the resistance of the reversing switch on the gearbox: Zero when out of reverse. 3-4Mega Ohms when in reverse - still quite high? Is this a normal reading for a closed reversing switch?

Also, one more question: With the ignition on, but engine NOT running, should the reversing light work? I'm assuming so, this would make the process of diagnosis much easier! ;)

It seems to be the case so far...

Cheers for any help you can offer!

Simon
 
As stated by Fanatic,Short out switch and check if bulb lights.
If it does,then switch is broken.

If it doesn't,then Put 12v feed to Green/black wire which goes to light and see if bulb lights. (check first)

Ign on provides 12v thru fuse to switch to bulb to ground. Llight comes on. If it's a glass fuse/holder,clean the ends of both with a some filwirewool,whatever.
 
Harleyman said:
As stated by Fanatic,Short out switch and check if bulb lights.
If it does,then switch is broken.

If it doesn't,then Put 12v feed to Green/black wire which goes to light and see if bulb lights. (check first)

Ign on provides 12v thru fuse to switch to bulb to ground. Llight comes on. If it's a glass fuse/holder,clean the ends of both with a some filwirewool,whatever.
Click to expand...

I have the same problem. How would you short out the switch and is this safe to do or would I risk blowing a fuse?
 
GreenLove said:
I have the same problem. How would you short out the switch and is this safe to do or would I risk blowing a fuse?
Click to expand...

Pull the connectors off the back of the switch and push a bit of spare wire, with the ends exposed, into each connector thus making the circuit. You are just immitating what the switch does, it is perfectly safe and wouldn't blow a fuse unless you are some sort of inept idiot.
 
GRATCH said:
Pull the connectors off the back of the switch and push a bit of spare wire, with the ends exposed, into each connector thus making the circuit. You are just immitating what the switch does, it is perfectly safe and wouldn't blow a fuse unless you are some sort of inept idiot.
Click to expand...

Excellent, thanks!

Do you know if the engine has to be running (and be in reverse) for the light to come on, or can I just turn the ignition to standby (engine off) and place the gear in reverse for illumination?
 
Station House said:
As Gratch says - just ignintion on

Sorry to offer a daft suggestion as sure you'll have checked - is the circuit fused? Presuming fuse is OK:eek:
Click to expand...

Now worries. Yes, checked and replaced all fuses with the correct amperage fuses last week.

Just finished shorting the two wires from the reverse switch, but no joy.

The wire going to the switch has power, so I'm guessing the break in the circuit must be from the switch back to the??? Does it go from the switch to the fusebox then to the reverse light, or straight from the switch to the reverse light? I'm guessing it's the former.

Perhaps I should next measure the resistance between the switch and where the wire runs back up through the engine compartment to wherever. My mechanic was playing around with the gearbox last week, so he might have pulled a bullet connection out or similar.

This is quite fun for my first dedicated electrical fault diagnosis, although I am operating with vain hope that the fault can be found without tracing the wire through the loom that's running through the fricking chassis of all places.
 
Right, replaced the switch, mended a corroded connection going from switch return to loom connection (in the engine compartment).

I know the wire going from the switch to the fuse box is fine because I blew the fuse by accidentally shorting the switch connection to the top of the gearbox :doh:

The next step is to test the wire coming from the fuse box to the loom (in the engine compartment) before it begins it's trip through the chassis to the rear.

Anyone have any idea what colour wire is coming from the reverse light fuse? I could unscrew the fuse box, but was hoping it was standard and someone would know.
 
GreenLove said:
Right, replaced the switch, mended a corroded connection going from switch return to loom connection (in the engine compartment).

I know the wire going from the switch to the fuse box is fine because I blew the fuse by accidentally shorting the switch connection to the top of the gearbox :doh:

The next step is to test the wire coming from the fuse box to the loom (in the engine compartment) before it begins it's trip through the chassis to the rear.

Anyone have any idea what colour wire is coming from the reverse light fuse? I could unscrew the fuse box, but was hoping it was standard and someone would know.
Click to expand...

It's a tangled, confusing mess. I seem to have two green wires coming from the back of fuse input three, one for the wiper and one for the reverse light, which are both green.

So to test whether there is current going from the fuse box to the loom in the engine compartment I'll have to use the sharp multimeter probe to pierce every green wire, then do the same when the connections appear at the rear cross member.

And it's drizzling. Bollocks!
 
Yoy should not need to puncturs all of the green wires to find a fault (honest).

According to the circuit diagram that I have from the fuse holder (listed as 12A?) two green wires (which are ignition switched & fused) leave, one to the front wiper motor (which enables the "park" function), and the second to the reversing light switch on the gearbox.

If you have 12v across the reverse light switch with the ignition on then that bit of electricity (from the battery / ignition / fuse to switch) should all be good.

If you then put it into reverse gear the 12v at the switch should go to zero volts, as there should be no potential across the switch.

If you still have 12v across the switch then there is a downstream fault to the light itself because there should be an earth by the bulb to create the lighting circuit which will effectivly pull voltage across the terminals of the switch to zero volts.

These may be any or all of the following:
Broken cable (which should be green with brown stripe from the switch to the reverse light), corroded, loose or open connectors, broken bulb, faulty or no earth, corroded contacts. All of these can be eliminated with time and tedium :)

Have you also tried a test bulb from the switch (bit of wire to switch - test bulb - bit of wire to a good earth). This will eliminate the switch if the test bulb lights. If it does not light, and there is 12v to the green wire then perhaps the switch is faulty, but as you say you have replaced it, has the switch been adjusted in such that it is activeted when engaging reverse gear?
 
skint-as-usual said:
If you then put it into reverse gear the 12v at the switch should go to zero volts, as there should be no potential across the switch.
Click to expand...

To test the new switch I connected one multimeter crocodile clip to each of the switch pins protruding out of the gearbox:

Out of gear = 1 / full resistance
Reverse gear engaged = zero / no resistance.

So I'm pretty sure the new switch is working as it should i.e. connecting the circuit.

skint-as-usual said:
If you then put it into reverse gear the 12v at the switch should go to zero volts, as there should be no potential across the switch.
Click to expand...

Sorry, but I really don't understand that one. When I did a voltage test to see if the switch was working (ignition on and reverse engaged) I got 12V going in and 12V coming out, which I would have thought was normal because the reverse switch simply connects the circuit. Am I thinking about this the wrong way?

After some more multimeter testing I got a little more info that I hope you can help me with:

Tested the wire going from the reverse light, back through the chassis, to where it appears in the engine compartment.

Result: zero resistance (all good.)

With the ignition on and reverse gear engaged I took a voltage reading (pierced insulation with probe and ground to engine metal) from the wire in the engine compartment, just before it goes through the bulkhead towards the fuse box.

Result: 0.026V (not so good.) What should the reading be anyway?

So judging by what you're saying, the fault is somewhere between the fusebox and where the wire appears in the engine compartment?

Incidentally, I'm about to take the dash off, if that helps.
 
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