Headlamp Voltage Drop

[tracksuit hobo]

On my 85 FJ60, the voltage started jumping up to 16v. I had the regulator replaced by my local Alternator shop, and everything worked fine as before.

While testing the system , the measured Voltage drop when the headlights were engaged was 1.1V.......I always figured it was normal since the blinkers dropped the voltage as well....but the tech was VERY alarmed. He says no headlamps should pull that much ....

To test, compare, and to prove his point, we ran the A/C. It dropped 0.2V

When I purchased the truck, the first thing i did was upgrade the headlamps to the H4 Hellas with 60/55w lamps. Huge difference, but should they pull that much power? As long as I can remember the Voltage dropped that much (very noticeable on the gauge), even with the older sealed beams.

The only other thing wired is a set of Hella FF1000's using the (straight to battery) Hella Harness, and no noticeable drop happens when engaged.

Bad ground? Bad Headlight Relay? Get an Upgraded Harness? Start fishing for shorts?

Would like to fix it before i start replacing regulators on a bi-monthy basis!

Any Info would Help - TSH

 

[djawahir]

I ran an 8awg wire from the alternator directly to the battery terminal and that fixed my wicked voltage swing problem. You may want to give that a shot first. I also grounded everything on the truck with 4awg braided wire. But the important part was the 8awg alternator wire. Hope that helps...

 

[lovetoski]

The 8 ga wire is a good idea - I've done it also.

The stock headlight wiring is long, and probably undersized - which results in a bigger voltage drop that ideal. An headlight hardness (with relay) is a great mod. My voltage drop essentially went to zero.

 

[tracksuit hobo]

Just did the 8awg wire jumper.....and voltage drop was the same.

Pretty sure i'll be making a wiring harness now.....might not fix the specific problem, but it will go around it and have a cool upgrade to boot.

thnaks for the help - TSH

 

[zebrabeefj40]

I also have H4 headlights and also get a decent drop in voltage when I turn stuff on. I have upgraded the alternator to a 105 amp Delco 21si from a school bus, upgraded the battery wire to 6ga and run an IPF headlight harness. Still get a little drop but not as much as before. Only thing I have left to do is replace the headlight harness ends as there is a lot of corrosion in the headlight connectors of my particular harness.

Nick

 

[lovetoski]

....there is a lot of corrosion in the headlight connectors of my particular harness.

Nick

I pulled every lightbulb and cleaned the sockets - lots of corrosion. Also replaced all the bulbs. Not only were all the lights brighter, but I measured less voltage drop as a result. Easy explanation - less corrosion = less resistance. Best of all - this is a free "mod."