On my 1991 Formula the passenger side headlight had started to go dim over the last week or so. I took the bulb out and switched in a known good headlight bulb and got the same dim result. I tugged on the headlight wire/plug a little and then the black (ground) wire came completely dettached from the headlight plug. So, it was a poor ground wire connection in the headlight plug that was causing the dim bulb. After doing a bit of reading on the site here..I could see that a dim bulb can often be caused by a bad ground.

I stripped the black wire...btw I used the my $2.99 HF wire stripper, http://www.harborfreight.com/cpi/cta...emnumber=66690
for the first time. The HF stripper was very easy to use. I pulled out the old plug/spade...and opened out the end of the spade connector - reattached the stripped black wire and headlight works fine.

So, if you are getting a dim headlight bulb and your ground looks good...try tugging on the headlight wires/plug a little..you might have a bad connection in the headlight plug like I did (and it is a bit hard to see).

 

If put some dielectric grease in those plugs after you clean them it will never happen again.