I have posted in Tech but wanted to try and get some info here too.

I have lost tail, side marker, brake, and gauge lights. They went out few weeks back driving home. I started checking fuses and things just started working again. Two week later same issue. Started troubleshooting, here is where I am at.

I have changed out the fuses, and the flasher. I did notice that the 20A Cig lighter \ Ctsy fuse was not installed, so I installed. With the battery re connected the interior lights came on seems like one of the door switches is malfunctioning because they did not turn off when the door was closed. What was weird is when the hazards were activated the interior lights kinda dimmed a bit and stopped working? I pulled the Cig lighter \ Ctsy fuse and went back to trouble shooting, all the tail, side marker, brake, and gauge lights were working before, and the interior lights can be dealt with later. So checked the connections to the brake switch looks good, looked at the harmonica connector and that looked good to. Where I am at now is no brake lights, no Hazards and no tail or parking lights. Turn signals are working. Not sure where to turn next, very frustrating, there were no indications of any issues until 3 or so week ago. Any further trouble shooting tips would be great. I have a multi meter and a 12 volt test light so I should be able to check some things out. I was thinking a grounding issue; can one component like a brake switch affect other circuits? Sorry for the long post but just put in 4 hours and have more questions than answers.

A few more hours and some more info. Jumped the brake switch no help, with one lead of a test light connected to the negative battery terminal for ground, the fuses for tail, stop and inst have no power.

Still trying to find the answers.

Any information would be greatly appreciated, I am hoping to enjoy the last month or so of the good weather her in the northeast, before really pulling things apart.

 

Normally light problems are caused by no grounds. Cleaning up the ground connections fix. But when you say you are on negative battery and no power at fuses point to the fuse box itself. I have noticed these fuse box clips seem to get corroded and even though the fuses are in they don't make contact. Taking out the fuses and cleaning clips with an ink eraser or fiberglass pen( bought at electronics store) and contact cleaner (spray) may help you.
If still no power it may be the connector coming and going from fuse box. Not an easy place to get to.
As for your courtesy fuse it sound like you have a partial short when you turn your hazards on. Easy to check your door switches with a meter as two wires and open when closed and shorted when open.
Alway start at source with meter and work towards light.

 

Pull the flasher relay out of the circuit on the fuse box and see if the brake lights, etc., are working. If so, the problem is with the flasher relay or related wiring to the harmonica connector.

 

trace your power. start at the power side of the fuses and see if there is power. if not check the power going into the fuse block. work your way back until you find power. all these things not working leads to what is common between them= grounds, fuse block

 

Looking at my 1973 wiring diagram I would check at the horn relay. This is a common point for jct of 5 battery wires feeding circuits.
You should ensure your connections are good here.
Also get a wiring diagram for your car. There is a forum member who has supplied them on request. Check forums for wiring diagrams

 

Thanks, All great advice, I will be back at it hopefully tomorrow. I do have a wiring diagram that I received from a member, actually I just printed it on 11x17 and laminated it. I think it will come in really handy. Again thanks for the information, and ideas. I will post as soon as I have some updates.

 

So I have done some more testing, main issues found

1. Bringing the brake lights (installing the bulb with the brake switch jumped) seemed to cause the stop light circuit to fail. I did have 12V at the socket with the switch jumped but would lose voltage if lights were inserted. Oddly enough a fuse would not be blown. I could go back to the fuse box and have no voltage at the fuse, however after working the fuse holder with the tester prod power would be restored to the circuit. I could then test the circuit from fuse box back to the light socket, all good. I also noticed when the tail lights were turned on the tail light and stop light circuit would lose power, but again back at the fuse box testing fuses with no power and after a few wiggles with the test prod voltage would return to circuits.

2. Fuse holders in the fuse box do not look good. Some oxidation, and corrosion.

3. Inst lamp fuse was almost falling apart, when I pulled it came out in two pieces.

Still very confused, however I am going to move forward with a plan.

I am going to remove all fuses, clean all fuse holders, inspect the fuse box for any damage and or lose screws\ connections. Re install all new fuses. Test all voltages at the fuse box for consistency and stability. Basically try and work out any issues at the fuse box first.

Work the stop light circuit - Start again at the fuse box and work back to the light socket on step at a time.

Do the same for the tail lights.

PS after pulling the basically broken Inst lamp fuse, and pulling and re installing the stop light fuse. (The one that seemed to respond to the prodding and wiggling the most) The tail light were working, turned them on and off several times with no issues, inserted the bulbs and they worked without causing the circuit to fail.
Once again sorry for the long post, and any information or thoughts would be greatly appreciated.

I will continue to update.

 

Removed all fuses &flasher, Sprayed the fuse box with air, sprayed the fuse box with CRC electronic cleaner. Cleaned all fuse holders with q tips, used a fine small file and lightly cleaned any oxidation, or corrosion I could see. Cleaned all fuse holders with q tips. Sprayed the fuse box again with CRC. Sprayed with air one last time. Installed all new fuses, used dialectic grease on all fuses. One of the holders seemed a bit loose, I paid close attention to that holder when I installed the new fuse, it seemed to be stable. Tested brake light & tail light circuits, both tested good. Cleaned tail sockets with CRC, and q tips, Installed new bulbs with dialectic grease. Tested tail & brake lights, both tested good. Tested the jumped out break light switch, it tested good. Reassembled break light switch, harmonica connector, and all lenses.

Brake lights, tail lights(and all marker lights) and turn signals all functional. Drove the car both Friday, and Sunday checking status each time. I also diagnosed my interior lights not turning off, checked both door jamb switches, and replaced a partially broken bulb. Cleaning all contacts along the way.

Thank you all for the advice, and ideas. The multimeter, 12V test probe, wiring diagram, and of course a lot of patience were critical. I also believe cleaning the fuse box and replacing all the fuses made a big difference. It's a good place to start if you have some funky wiring issues.

Thanks again.

 

the fuse clips are typcially so corroded they will not conduct or do it intermitantly.
and make poor contact with the fuse, when testing for voltage touch the clip not the fuse body.

 

Best advice I can add is to sit down with a good electrical diagram that you can see and read and start visualizing how each circuit works and where it gets ground/power from and the sequence of events to make that circuit operate.

Than start the process of troubleshooting each individual circuit. I prefer to start with making sure I have 1) wire continuity, 2) ground and than move on to 3) power. Somewhere along the way working through 1, 2, 3 you will find your problem.

 

Thanks, I have Brake, tail, turn signal and instrument lights all working. The multi meter, 12V test probe, wiring diagram, and of course a lot of patience were critical. I one circuit at a time, from source to light. Thanks, again for all the great information. It has been a while but after a bit I was back into it.