Hi. Just went to take my 71 "S" out for a spin and noticed the headlights weren't coming on. None of them,not the regulars or the high beams. they were all working up until last week, last time i drove at night. the instrument panel lights dim and brighten when i turn the ****. the turnal signals and break lights are all working. noticed also the dome light is not coming on. no other electrical problems that i know of. i have a knew alternator,battery and voltage regulator installed and the battery is being charged by the alt, i have aftermarket gauges installed. tried searching online and searched here for past threads. also referenced my chassis service manual but can't find where the fuse is, the fuse block diagram does not list headlights. is there one? i know the headlight switch has a circuit breaker but the lights aren't flickering, they're just dead.

 

That's a tough one. Old car wiring (40 years) can be a PITA. I would start at the front and work my way back. Check the plugs at the bulbs and all of the grounds. There are some wires that bolt to the header panel to ground the headlights, Make sure they are tight and clean.
Then follow the wires back to the bulkhead connector on the firewall and make sure there are no breaks in the wires anywhere. Then you can move into the cab and check the fuses. The headlight fuse should also control the parking lights, so if they work the fuse is most likely not the issue.
The next stop would be the floor mounted dimmer switch. You may need to remove it to inspect the connections and make sure they are clean and good.
Last on the list will be the headlight switch it self. It can be a pain to remove so save this for last.

This is from a 70 FSM, but the wiring should be really close.

 

there didn't seem to be a fuse marked headlights on my fuse panel though, and the description in my chassis manual of the fuse panel doesn't list one either. is it not on the fuse panel directly below the steering column?

 

OK I just took a closer look at the schematic. If you look closely at the main light switch at the bottom of the picture you will see that it is fused by a fusible link that attaches at the horn relay on the drivers side fender. That is where it gets it's power from. The switch then sends power to the foot switch via the blue wire and the foot switch decides if it should go to the low or high beam lights.

So my thought it it's either the dimmer switch or the headlight switch it self as there just isn't that much to go wrong in the system.

 

my chilton manual says that there are two fuseable links coming off the starter solenoid (both red wires). if the headlights are not coming on but all other electrical systems are working then one of those links has to be replaced, if its the opposite with the lights on and nothing else working then its the other one. i'll check those first and then work backwards to the dimmer switch and main switch. sounds like its those links as that's exactly what's happening.

 

They are NOT at the starter, but located on the post of the horn relay on the drivers side fender.
I don't trust the Chilton or Haynes manuals. They are either incomplete or just plain wrong with a lot of their information. The scan I have is from a 1970 factory service manual.

 

update: got them to come back on. seems the plug going into the foot dimmer switch was a little corroded so i cleaned it up and it started working again. the switch itself seems fine so i think its just the plug that should probably be replaced.

 

Good deal.