Technical Reversing Light

[Patspiercing]

Hi,

I have a problem with the reversing light on my 1999 Barchetta. It is totally doing my head in.

The reversing light does not work.

I have removed the light and checked for 12 volts on the wiring connector and I am getting that. I checked the bulb and that is ok. I cleaned the connections on the bulb holder but it still doesn't work.
I then removed the fog light and tried plugging that onto the wiring connector and that doesn't work. I plugged the reversing light into the fog light wiring and it works fine.
I have tried putting a pair of wires into the reversing light wiring socket and I definately get 12V. I then tried connecting them directly onto the bulb and it doesn't light.

The gearbox switch MUST be ok because I am getting 12V so what can be the problem?

To Summerize
1) I have 12V to socket
2) The light and bulb works
3) they do not work when I connect them together

Any ideas please

 

[GettinBetter]

Long shot here, but:

• Are the contacts in the housing spring loaded?
• Any pics?
• One or two contacts.
• When the bulb is twisted to lock it in, does it still line up with the contacts?

 

[Patspiercing]

Hi, Thanks for the quick response.

The contacts are not spring loaded
There are 2 contacts.

When I plug the complete light unit into the rear fog light wiring plug it works, so it cannot be the bulb holder. When I plug the complete rear fog light into the reversing light socket that doesn't work either.

I get 12v when I put the probes against the 2 contacts, I do not even have to push them inside.

The only thing I can think of is that I am losing the 12v when the resistance of the bulb is connected across it. But I cannot think of any way it could do that

 

[Mike1alike]

I have tried putting a pair of wires into the reversing light wiring socket and I definately get 12V. I then tried connecting them directly onto the bulb and it doesn't light.

Means you don’t have ground at the bulb, doesn't it...?!

 

[GettinBetter]

The contacts are not spring loaded

They may not be conventional circular springs, but they are springy tabs? So one should be live and the other grounded.
How are you measuring the 12V that you say you have. one meter probe on one tab and the other meter probe on the other tab?
Can you supply a picture of the bulbs housing?

 

[Patspiercing]

If I was missing the earth I would not get 12v across the 2 terminals. I am measuring across the 2 terminals. The bulb holder must be good because if I plug it into the fog light it works

 

[Mike1alike]

The plug (and probably bulb too) have oxidised contacts there, that's why bulb doesn't work. Use contact spray and/or scrape the contacts clean as much as you can.

 

[Patspiercing]

I have scraped the plug and bulb contacts as I thought that was the problem.

But if I plug it into the fog light socket it works, so that can't be the problem.

This is why I am pulling my hair out trying to sort it out!!!!

 

[Mike1alike]

I have scraped the plug and bulb contacts as I thought that was the problem.

But if I plug it into the fog light socket it works, so that can't be the problem.

This is why I am pulling my hair out trying to sort it out!!!!

Obviously the problem is with the reverse light plug connectors/reverse light socket!

 

[Patspiercing]

I have also tried using the bulb and holder from the fog light in the reversing light and that doesn't work.

I am getting 12v at the plug without even pushing the meter probes into the socket, just touching them on. So I don't think that is it.

I have tried using an old motorcycle indicator and pushing the wires into the socket and that doesn't work either. I am reluctant to cut off the socket and fit another one as the car is very original and has only done 25K km.

 

[puntodad19]

The lads Punto had a r/h/side rail light intermitant problem that would show up on the dash warning system.

The fault suggested to me a "bad earth" from time to time.

Using a dmm set to buzzer continuity suggested the tail lamps earth track had a high resistance between track and connection earth pin, just st where the earth track ( and others ) were plastic riveted, a plastics pip, heat deformed, to hold the tracks in Place.

A dedicated extra earth soldered to the he lamp unit earth track, and connected to the car body convienient hole, via a "bulleted" flying earth lead, cured the problem.

Difficult to believe but there you are.

Does your black "car loom connecter" pass the dmm "voltage presence" test, earth continuity test, and a "load test"...?

A load test equivalent to the wattage of the bulb that connection supplies...

You say you do not want to replace that particular possibly "dojjy" connection...


Do a load test....on those wires....

 

[Patspiercing]

I have used a nultimeter to test for voltage between the 2 pins and get 12V.

If I connect a bulb directly to the socket it does not work, so that suggests it is losing the voltage under load.

I will try connecting the bulb to the live 12V socket and earthing direct to the battery and report back. It will probably be tomorrow.

Thanks for your suggestion

 

[puntodad19]

A load test from the yellow? 12 volt supply to body earth, system works, yes, so yellow supply line ok.

Load test from yellow supply wire to black earth wire, system does not work, fault in black earth wire under load, even though continuity test suggests earth is ok.

Wire broken inside connecter, a bad connection at its earth point, or somewhere in between....?

A "pin probe" through the black insulation, or just renew wire run...

It's probably a make and break connection inside the black two wire connection....

Enjoy, report back with conclusion.

 

[Mike1alike]

Surely there lies your problem. Maybe there is something inside that make connectors touch each other, short cut, when you plug the holder in. Get the connectors out and make sure everything is in order.

 

[puntodad19]

I do not believe you will be able to remove the connection *female spades* from inside the black car loom connection block, they seem to be "sealed" in place.

Someone mention "servicall" spray contact cleaner, available from *rapid electronics* and other suppliers. Very good stuff.

Mike has said that the two female spades connections may be dirty. They look a bit dirty in the photo....

 

[Mike1alike]

Yes, they do look dirty. Contact spray would do them good.
But can be more than just, as I said. Can be a short cut there when holder is connected. So needs to be checked.
And although seem unlikely, every connector (be it female spades - careful @puntodad19 not to get suspended again! ) usually can be removed with care. (And that's how every female should be treated - with care )

 

[puntodad19]

Yeah, you don't want to bugger it do you..

 

[Mike1alike]

Yeah, you don't want to bugger it do you..

Or... do you...?!

 

[Davefridge]

Yeah, you don't want to bugger it do you..

My guess is that testing with a multimeter is giving false info. There is probably enough power/voltage getting through to give a12v reading but not enough to light the bulb. This could be due to bad connection anywhere. Is it possible to bypass the gearbox switch?

 

[puntodad19]

If ignition is on and gearbox in reverse, them 12 volt appearing at the yellow ( or is it white ? ) Terminal in the black loom connector, all good, but.....insert a prepared wire into the same connection, connected to a suitable "load", like a 21 watt bulb, with a wire connected to a close body earth, then the wiring from the source, thru the load bulb, then to earth, with the bulb lit, tests the circuit as working.

Now earth via the black connecter black earth wire, same conditions, but with the bulb now not lit, would prove a bad earth, surely....

No matter what is involved in the circuit, fuse, gearbox switch, body computer controling lights etc., will be tested and either proved to work, or not.....

I suspect, the wiring diagram will show, that the light in question is earthed, via body, rather than being "sunk" thru an electronic unit.

Electronic units, usually, but not always, sink more current than source...

The op has a m/cycle "test load" but may have not earthed it via car body directly, yet.