Blown fuse...

[lipunx]

My friends Golf is blowing the fuse for the marker and tail lights on the drivers side. It'll hold till you rev it up or drive around a little bit. I'm pretty sure it's a lost cause since it's such a weird problem but I figured I would ask anyways...

Thanks in advance

[Mr_Diesel]

Get a voltage tester... put the red (positive) lead on the positive battery terminal and the black (negative) on the other terminal.

When the engine is off and key is turned off you should be getting approx 12V from a fully charged battery give or take 0.5V Start the engine... give it a quick rev to 2,500 to activate your alternator... At idle with all the accessories and everything turned off you should be getting a voltage reading of approx 14.5V give or take 0.5V. Now get a friend to rev it up and hold it at about 3,000 rpm.... see if the voltage changes. If the voltage spikes then your alternator or the alternators voltage regulator may be bad or going bad. Anything above 16V is getting dangerous. Now, since you are under the hood with a voltage tester you might as well test your alternator to see if it's up to snuff. Turn on everything in the car. Headlights, rear defrost, AC blower, radio etc. Take a reading on the battery again... With all these things turned on your reading should still be above 14V. If it goes anwhere below 13.5 give or take 0.5v your alternator is probably showing it's age with diminished output.

If everything here checks out, then it's probably that damn electric VW squirrel burrowing a nest in your wires and fuse box... AT this point it might take a professional to diagnose the problem.

Try upping the fuse amps by 5... Most of the fuses that run simple circuits for the small lights are fuses are like 10amp... so just stick a 15 in there... try it again. If it pops the bigger fuse, then yeah... something is shorting out. If the fuse doesnt pop, your problem is solved. Don't go any higher than 5 amps above spec or you might run into other problems... Going up just 5 amps should be safe though.

It's highly unlikely that your alternator or voltage regulator is popping just this one fuse, but hey... it's all about a process of elimination... It wouldnt hurt to know about the condition of your alternator or voltage regulator.