# Reversing light not working



## vicdicdoc (May 14, 2005)

Whilst away this weekend our friends mentioned that the reversing light wasn't working . . . being [big headed ?] I stated it was one of four things . . (1) the bulb u/s (2) the reverse switch in the gearbox u/s (3) a blown fuse or (4) a wiring fault.
(1) We removed & tested the bulb - result - works ok.
(2) We turned on the ignition & selected reverse - result 12.28v being shown on my multimeter.
(3) We put the multimeter across the pos & neg wire to the bulb 
holder - result 12.28v.
(4) We checked ALL fuses - result all ok
we were both totally confused :? . . if there was 12.28v across the connections why wasn't it working ??? . . Am I missing something [obvious to everyone but me] ?


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## clodhopper2006 (Aug 13, 2006)

bad contact on the bulb. Give it a good clean. Scrape the pos terminan on the bulb with a coin.


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## vicdicdoc (May 14, 2005)

clodhopper2006 said:


> bad contact on the bulb. Give it a good clean. Scrape the pos terminan on the bulb with a coin.


Done that but still not working !


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## erneboy (Feb 8, 2007)

If there is power at the socket from which you removed the bulb then the fault is there. Have you tested the bulb with your meter, it may look ok but still not be working. If you get continuity through the bulb then the connections are faulty/ corroded or the bulb is a loose fit, Alan.


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## Tezmcd (Aug 3, 2009)

by way of limiting the area of investigation

1 - Does the offending bulb work correctly in a different holder?

2 - Does a different (previously proven to work bulb) work in the suspect holder?

If 1 works then its not the bulb at fault
If 2 doesnt work then its the holder

If 1 works and 2 works then its a bad area of contact between that bulb and that holder (which I have seen before)


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## clodhopper2006 (Aug 13, 2006)

vicdicdoc said:


> clodhopper2006 said:
> 
> 
> > bad contact on the bulb. Give it a good clean. Scrape the pos terminan on the bulb with a coin.
> ...


OK well if you definitely have 12v at the fitting and the bulb measures good then it must be that the pos terminal on the fitting is either dirty or not touching the terminal at the base of the bulb. 
Use a pair of long nose pliers to bend it forward a bit. Make sure the ignition is off and you're not in neutral first.
Incidently how many ohms does the meter say the bulb measures?


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## clodhopper2006 (Aug 13, 2006)

just re read this point


(3) We put the multimeter across the pos & neg wire to the bulb 


test the voltage at the contact points in the fitting not the wires.


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## thesnail (May 1, 2005)

*still don't work*

Hi Guys,

It's my van with the faulty reverse light.

Bulb is Ok, it checks for continuity and also been replaced with a proven to work bulb and a new bulb.

There is 12.6 volts in the bulb holder, we also bypassed the bulb holder and connected the wires directly to the bulb, still no luck!

Will prob end up selling the van, seems to be the only way to rectify the problem.

Note:- there is a reversing camera fitted with a wire connected to the bulb holder, as this may have caused the problem, I have disconnected that to take it out of the equation, --*HELP*-- !!!!

Bryan


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## clodhopper2006 (Aug 13, 2006)

yes but is the pos terminal actually touching the bottom of the bulb?


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## thesnail (May 1, 2005)

*touching*

YES! Actually connected the both wires directly to the bulb

Bryan


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## clodhopper2006 (Aug 13, 2006)

When you measured the resistance (continuity) of the bulb element what was the value you saw in ohms?


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## vicdicdoc (May 14, 2005)

clodhopper2006 said:


> When you measured the resistance (continuity) of the bulb element what was the value you saw in ohms?


Surely a 12v bulb is a bulb is a bulb regardless :?


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## corgi (Mar 9, 2007)

Bryan
Had a similar fault a few years ago.
12v across bulb contacts with meter but no light with proven bulb.
As you did connected wires direct to bulb still no luck.
Then connected +ve wire from lamp holder to bulb and another wire from proven earth (chasis) to other contact on bulb, Hey Presto bulb lit.
It was a poor earth good enough to indicate 12v on meter but to high resistance for the lamp to function.

Hope this helps

Trevor


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## clodhopper2006 (Aug 13, 2006)

vicdicdoc said:


> clodhopper2006 said:
> 
> 
> > When you measured the resistance (continuity) of the bulb element what was the value you saw in ohms?
> ...


Well were sure there is 12v to the bulb but it aint lit. Voltage test has been done between the terminals of the fitting so we know voltage is present. Now we know it isn't blown but if it's resistance is too high you may get a continuity bleep but it won't draw enough current to light it. Can happen with a dead bulb.
Either measure it's resistance or replace bulb to illiminate that

edited due to blond moment


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## peaky (Jul 15, 2009)

sounds a bit complicated to me, we too had bulb issues, if we put a reversing bulb into the holder the front nearside headlight came on, take it out and then the front headlight came on when braking, rear offside light just didnt work and three of the four top little lights on roof refused to work also. been like this since we bought it 4 months ago, we only drove it during daylight as the indicators and brake lights were the only consistant thing to work (although i had replaced the side indicator bulbs cos they did nt work ) been to garage this week, 3 hours labour, 3 new bulbs and 75 euros later all fixed, she now lights up like a christmas tree !!!! wonder what it was crossed connections ??????


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## clodhopper2006 (Aug 13, 2006)

It's really simple. In your case it very much sounds like an earth fault causing current from one circuit to travel through another circuit using the other circuits earth path.
In the cse of the OP it's even more straight forward. He has a voltage at the bulb therefore he has a circuit. If the bulb is inplace he should have a resistance to complete the circuit. Voltage through a resistor of say 12 ohms gives a current typically say 1 amp giving 12w of heat and light. Increase that resistance to say 120 ohms you sudenly find your current flow down to a theoretical 0.1A and no visible effect.


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## erneboy (Feb 8, 2007)

That is interesting Bob, my electrical knowledge does not extend beyond basics. The bad earth lighting other lights bit I knew, Alan.


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## clodhopper2006 (Aug 13, 2006)

corgi said:


> Bryan
> Had a similar fault a few years ago.
> 12v across bulb contacts with meter but no light with proven bulb.
> As you did connected wires direct to bulb still no luck.
> ...


Yes I agree this may be the case here too.


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## thesnail (May 1, 2005)

*Thanks for help with reverse light*

Thanks everyone for your help with my problematical light.

Does seem that a poor earth may be the problem I will investigate as soon as it stops raining.

Thanks again

Bryan


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## emmbeedee (Oct 31, 2008)

Agree with the above, most probably a poor earth. Searching for these sort of problems is easier with a test lamp, IMHO, than a multimeter. Multimeters (especially digital ones) only require a miniscule current to show voltage, as in this case. If there is a bad connection anywhere in the circuit, on the positive or the negative side, it can pass enough current to work your multimeter but not enough to light the bulb.
Suggest you connect an extra earth cable to the bulbholder temporarily (earth side obviously) & insert bulb. If it lights, poor earth is the problem, if not poor positive connection is the problem. With a simple test lamp you can just go back along the circuit, checking each connection in turn until you find the culprit.
I first came across the missing earth problem on a brand new Harry Potter Ford Anglia in 1959. Brake lights putting tail lamps off, indicators causing other lights to flash, etc., etc. Driver had been to three different Ford dealers who couldn't sort it, one suggested a new loom was necessary.
Not wanting to lose the car whilst they had it in for goodness knows how long, he asked me to look at it. (Even back then I was always working on cars.) Nearly drove me mad, all connections good, as they should be, being brand new. :? Eventually after much head scratching & studying of wiring diagram worked out the problem, no earth connection at all to RH tail/indicator cluster. All nuts were tight, but paint or something must have been blocking current. 
Easily solved once identified, I made up an earth lead from the lamp to the vehicle body & everything worked as it should. Never forgotten that lesson, though. Any cases of bizarre happenings with vehicle lamps, always check for a good earth first :!: 
Seemples, as the Meercat says.


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