The Funny Thing about Wiring-

Whether you need to do a simple repair or a major wire harness replacement, you're going to need some common sense and mechanical aptitude. In a previous example, I talked about a bulb being placed into the socket incorrectly. Well, OK- we probably got to that point from a car that blows the directional fuse, fast or slow turn signals or seemingly unrelated lamps coming on or dimming when the directionals were turned on.

This symptom could have been a couple of things, especially in a car that has corrosion issues. But after the laying on of hands, some things should jump right out. Has someone messed with the wiring before, maybe added a trailer harness for instance? Following the basic harness at the affected part could also reveal collision damage, even if correctly repaired, a ground or other connection could have been replaced carelessly. And corrosion won't be limited to older cars- a cracked lense or socket could allow water in on even a fairly new vehicle.

Be sure to look inside the lamp socket or at suspect connectors, very slight corrosion can make all sorts of weird symptoms appear. Be prepared with a very small pick tool or file, and gently burnish any connection or contact that doesn't look nice and clean. Things can move out of position too, maybe a bulb was forced into place and the contacts will not touch the base even when installed correctly. Di-electric grease can be used to protect the connection(s) once the repair is verified.

OK,  nothing funny here, just common sense.