Clean/tighetn all tattey cables/grounds etc & tighten the alt belt.
It is normal for the lights to drop some esp at a low idle with auto trans car with only a 37 or 42 amp alt.
You battery could also be a little weak to adding to the light intensity/voltage drop at idle when the alt isnt putting out much umph.
After you clean all connections check electrolite level in battery and add distilled water only if its below the plates and then recharge it.
After that start the motor with a volt meter on battery and if you get approx 13.5-14.5 volts with the motor at 2k rpms no load and then approx 13-13.5 volts with headlights and heater fan on with motor still at 2k rpms you should be ok.
If car is starting ok i would not worry about it at this point after cleaning the cables and checking the battery lvl but if you can raise the idle a little i would do that.
You could have your local shop do a load test on the battery to see what cont its reallty in,autozone/pepboys etc do that for free where i live.
If your running a 37 or 42 amp alt they are marginal at times,you could find a good automotive electrical rebuilder shop that could upgrade your exisiting low output 37 or 42 amp aly to 55,61,0r 63 which were h/d charging options back then or they can install an upgrade for approx 70-80 amps,i had the 80 amp upgrade done to my stock 37 amp unit in my 69 velle/396.
scott
