I have a 98 mustang that I am having a light problem on. The right headlight is really dim and I can't seem to fix it . I have put in a new headlight switch bulb and a new lens but still no good . Any help would be appreciated
The BEST way to fix your problem is with a through visual inspection followed by perform a voltage drop test. This will help pinpoint WHERE the weak electrical connection is (positive or ground).
The concept of how to perform a voltage drop test can be found here:
The information is about charging system but the concept is the same.
For example. If you suspect the problem is in the ground then put one lead of the VOM on the terminal with the black wire and the other on the battery negative. Turn the head lights on and measure the voltage drop. Do the same thing for the positive side. Compare the results. Focus first on the side with the greatest voltage drop.
^ I agree. Most likely culprit in my experience is weak ground. the circuit is loosing voltage to the light because it's having to push through a patch of resistance at the bad ground. It's not broken, but corrosion or a loose connection is causing resistance in the circuit.