I have a problem with my headlights when i press the brake pedal, the headlights dim a little and when i let go of the brake they turn back to the normal brightness. Also wat i noticed when i break wit the light off the battery gauge goes down almost to 10 volts and wit the lights on it goes down to 8 volts. I checked the alternator and is good. could it be a short somewhere or something needs more ground? I have a 1984 GS

 

mine goes down just bit but not that far i found that the heater fan was worste than the headlights

 

Hey Trailhand,

I take it that this is a recent incident. If so suggest you "load test" your battery. Most service stations have one, It tests your battery by putting a "load" on it as if you were starting your car or running a bunch of accessories. If the battery is "old," or "dying", it's time for another. Also how did you "check" your alternator? Did you take it off and take it to auto supply house for a test? If not, do so.

Lastly, but more simply, check your belts. Are they old and worn, loose?
If so replace or tighten as needed...

Santa Claus is comin'....

Denny, from the 'ol corncrib....

 

You might have lost a ground in your brake wiring. Check your diagram in the Haynes manual and find out what color it is and see if it's grounded. There should be one near the brake lights, somewhere back there. Hope this helps.