[Pierceb.lewis]

Hi All,
The performance of my lights is become a real nuisance of recent. I've refurbished the lenses and keep them polished yet there wasn't any improvement after the last time I did so. Alternator seems to be putting out over 13v on idle however only 9v is getting to the lights? Any suggestions to what could be causing this?
I know the mk4 golfs and T4's had poor lights and you could buy aftermarket relay assemblies which would provide battery voltage to the lights, I think this was due to the voltage drop within the standard circuits, is it the same for passats? I've had the car for going on 4 years and they seem to be getting worse.
Many thanks for reading, I look forward to reading any replies.
Pierce

 

[Iowegian]

I'd say it is almost certainly a voltage drop in the circuit that powers the headlights. For some reason, it seems that the majority of cars these days have under-capacity headlight wires and the Passat is no different.

Pull the cap off the rear of the headlight assemblies and check the wiring, it may be already damaged. If those wires are bad, you'll have to replace them or the head light assemblies. If that wiring is OK the voltage drop is somewhere else. You can measure the voltage drop across various points of the circuit with any old DC voltmeter. Find the weak point(s) and upgrade those wires or connections. Relays reduce the load that goes through the light switch and can also act as a 'remote' switch so the current path from the 12V source to the lights is shorter. Don't forget any current going through the lights must also travel through the grounded side of the circuit back to the battery so be sure to check the negative side of the light circuit to see how much voltage drop is on that side. The problem could be as simple as a dirty or loose ground wire somewhere.

 

[Tomvw]

Are you only getting 9V to the high beam lights ?

The low beam lights normally run on about 9V as daytime running lights.
If they don't go to about 12V when the headlights are switched on, maybe you have a faulty switch.

 

[ylwagon]

That's a good suggestion. All the headlights get current through that headliight switch, so if both high and low beams have the same low Voltage, check there. Four headlights all dropping 4 Volts at maybe 4 Amps each would be cause about 60 Watts of heat, enough to smell something burning I'd think.