I have a '77 Early Bronco with a problem. Let me start by saying the wire harness is not spliced at all and is in very good shape. When I start the vehicle the ammeter is roughly at 0 (Early gauges are not very accurate). When I drive down the road everything is fine. I can use the radio, heater, and interior light until I turn on the Headlights. Then the ammeter will jump around (always staying above 0) and all the lights on the truck will get dim then bright again...almost like a flickering effect when I am going down the road or above idle. When I stop or I am at idle the lights will go dim....not so dim I can't see but dimmer than when I am above idle and they will stop flickering most of the time. The second I turn off the headlights everything goes back to normal. I have been rebuilding the vehicle and have spent alot of time and money to ensure everything is correct. I have new Heavy Duty Battery Cables, new starter solenoid, new voltage regulator (replaced twice), New Headlights, New Alternator (Tested 5 Times at local shop), New Battery....but is not correct size for battery tray....don't think it would be a problem as it starts every time and runs no problem. I did notice if I leave the lights on to drain some power out of the battery for a little while and then turn the lights on after I start the truck the ammeter will go to +30 or +60 depending on how long I left the lights on and it will eventually start jumping again. I heard there is a breaker of some sort on the headlight switch that could be causing my problem, but I want to cover all my bases before I go spend some money I don't need to. Has anyone ever had this problem or anything similar? I could use the help...everytime I drive at night the people in front of me think I am flashing them. It gets annoying after a while. I would appreciate the help....thanks

 

The breaker in the headlight switch will cause the headlights only, to go completely out and then come on again. None of the other lights are affected by this breaker.

My first thoughts are there may be a grounding problem to the front sheetmetal. That is where the lights are grounded, and probably also where the regulator is bolted and gets it's ground.

Take a voltmeter and take a volt reading on the + and - battery terminals with the truck off. You should get around 12 to 12.5 volts. Then with the engine running, take a reading again. It should be anywhere from high 13's to 14.5v roughly. If you are getting readings way out of this range, say 16v or higher, that is saying there is still something wrong with the charging system. Also with the engine running, turn the headlights on, and then while they are going dim/bright, take readings at the battery again. If the voltage is going wild at the battery, then this confirms the charging system does not have control of the situation.

You had everything checked over and over, so I hope the grounding problem is what's causing it. Take a short piece of wire and bolt it to the block, and then bolt it to the firewall. You may want to run some more to the radiator support or near the regulator. The number of grounding wires you need to run will depend on how rusty the sheetmetal is, or it could be a case of it being restored and there is too much paint where the metal is bolted together.