Hi boys/girls..

im trying to help out my brother in-law, his 94 f-150 8cyl. lights would dim than brighten.. doing this back and forth in sync with the charge guage when it was idling.. give'er gas, the guage stabilized...
so..... he changed the belt, no difference.. changed the battery... no difference.. changed the alternator, no difference... still has the fluctuating guage, headlights, etc..
Now, ive been searching alot of posts... found a couple which sound similar, such as bad connections... especially grounds, and wires where high voltage is... they need a real good connection...

but with the components that have been changed, and the factr that revving seems to help... does anyone have a better explanation or one at all.. lol

thanks..

 

Certinaly the lights will change brightness when the system voltage changes over a several volt range.
Check out the plugup at the alternator for corrosion or being over heated.
It likley moves with engine movment under acceleration and loses connection.