Technical GP '09 - Roof and boot lighting - low voltage

[francocm]

Hi all,

So I recently bought a July 2009 Grande Punto 1.2 car which I'm very happy with.

Immediately I had noticed that the interior roof light was not powerful. I had dismissed this to a low quality led bulb, and planned in mind to simply replace the bulb. Eventually I replaced it 3 times and never satisfied with the luminosity. Again I blamed the cheap eBay LEDs.

Then recently I bought an led strip for the boot, and to test it quickly I connected it to the cigarette lighter socket and it shone so happily, I connected it to the boot circuit... Again, dim light.

At this point I realised that the problem might not be the bulbs but the actual car. So I got myself a volt meter and surely the voltage for these lights is 6V, whilst I'm expecting to see 12V. This explains why the bulb shone a lot better when connected with the cigarette lighter as it provides 13V.

This voltage is constant irrespective of whether the engine is started or not.

Anyone encountered this before or has any idea where the issue might be?

Thanks

 

[francocm]

So guys, I did some few more tests and noticed the following:

Test #1
Condition: LED bulb connected to roof light socket
Result: 6V measured between the + and - of the connector. Bulb lights up but emits a weak light

Test #2
Condition: No bulb connected
Result: 12V measured between the + and - of the connector

Test #3
Condition: Traditional incandescent bulb connected
Result: Bulb doesn't light up. Approx 0.2V between the + and - of the connector

Basic physics tells me that for this kind of behaviour to occur, there must be another component connected in the same circuit, with a very high resistance.

Now, whatever this component is, I do not know, although I suspect it would be related to whatever controls the dim effect on the bulb.

Anyone has any idea of how the rest of the circuit is made up? Anyone can provide links to this particular wiring diagram?

Thanks a lot guys

 

[Andy Monty]

See our downloads section you need to mount and burn all parts of the elearn to a CD ROM

 

[francocm]

See our downloads section you need to mount and burn all parts of the elearn to a CD ROM

Thanks. Will check it out

 

[aurick86]

You are right on the resistance.
High resistance can be caused by a bad connection somewhere in the circuit, on the + side or on the ground.
You can easily find out which one is causing problems by alternately trying one of the + or - (of the connector) with either a GOOD body ground, or a +12v directly from the battery.
I hope i made myself understood.
Always measure the voltage under load ( better use the original incandescent light bulb for this.

I would suspect a bag ground.