New World Datsuns...

So this is a new one for me. I got the red wagon driving smoothly and somewhat reliably. I can drive it during the day all I need, but when I run the headlights for a while while driving they die out after about 5 minutes and then some seemingly random electrical problem follows.


First time around they just shut off and no lights would work at all for anything until I let things sit for a minute (and cool down?). I thought I solved it by cleaning all my grounds and making sure all was in order there, but now that's not the case. Today it happened again, but after I shut everything off, my dash lights all stayed on, no matter what I did with the headlight switch. I disconnected the battery, then reconnected it. Everything was off again and my headlights came back on when I pulled out the switch. It all worked normal like disconnecting the battery reset something.

Bone stock electrical system on a 71 510.

Anywhere in particular I should start looking? Or should I just start digging though the harness with a test light and multimeter until something seems funky?

Bad headlight relay?

Never gave me any trouble before... But I'll look into it. I'd rather replace all the relays with modern parts anyways.

Yesterday when it happened the body grounded to the engine via the return spring, causing my throttle to stick and the spring to stretch.

Try tapping the relay,if it happens again,it "should" click off

If it is grounding threw the throttle cable, then the engine/battery ground connection/cable is bad, or the engine to body ground/cable is bad.
The one time I goofed and and left the ground cable from the engine to the body/frame ground loose, my throttle cable melted to its sleeve at half throttle, I was lucky and just half a mile from home, so I fast idled all the way home on back streets.
Check all your battery cable size cable grounds, battery to engine, engine to frame, and frame to body, they all have to be there.

i would imagine maybe your light switch is fucked. Take it out, take it a part and look inside of it.

Neighbors mustang was doing the same thing. Replaced the headlight switch, done deal. May not be your case, but that's why i suggest taking it apart and looking inside of it. Could be all corroded and dicked up.

Head light relay, and light switch have the full current going through them. If either are a bit corroded, it increases resistance and will heat them up to a point of failure.

Are you killing fuses?

Ill also see if I can get a write up about switching to a modern relay. I have done this...

I'll check the switch and relay after work tomorrow. Oddly enough, no fuses blew.

levigideon wrote: Today it happened again, but after I shut everything off, my dash lights all stayed on, no matter what I did with the headlight switch.

No fuse is going to power the dash lights when the switch is off. This is likely a failure in the headlight switch.

If you are careful you can pry back the folded metal tabs that close the switch to hold the parts in. Have a care as you may only get one chance. Bending these tabs more than once may snap them off. You can take out the sliding parts and the brass contacts and clean them. May even be something in there that's broken like a spring.

To remove the switch unplug it first. Pull switch out fully. Grip the brass stem tightly with needle nose pliers and at the same time push inward on the knob and turn to release it. Now loosen the nut on the front of the dash and push the switch through and retrieve.



A short is a path around a load to ground and would either blow a fuse, which is what they are supposed to do, or melt a wire starting a fire. An open (or bad) connection would cause the lights to go out. This could be a dirty or worn contact, often intermittent. The dash lights staying on could be something loose/broken inside the switch making contact where it should not. This would not be a short strictly speaking.

The lights going out could also be a poor fuse contact that heats up and 'opens'. So replace the headlight fuse and check the fuse clips are clean and grip the fuse securely. As stated this won't cause the lights to stay on. Likely both problems are in the switch.

datsunmike wrote:

levigideon wrote: Today it happened again, but after I shut everything off, my dash lights all stayed on, no matter what I did with the headlight switch.

No fuse is going to power the dash lights when the switch is off. This is likely a failure in the headlight switch.

If you are careful you can pry back the folded metal tabs that close the switch to hold the parts in. Have a care as you may only get one chance. Bending these tabs more than once may snap them off. You can take out the sliding parts and the brass contacts and clean them. May even be something in there that's broken like a spring.

To remove the switch unplug it first. Pull switch out fully. Grip the brass stem tightly with needle nose pliers and at the same time push inward on the knob and turn to release it. Now loosen the nut on the front of the dash and push the switch through and retrieve.



A short is a path around a load to ground and would either blow a fuse, which is what they are supposed to do, or melt a wire starting a fire. An open (or bad) connection would cause the lights to go out. This could be a dirty or worn contact, often intermittent. The dash lights staying on could be something loose/broken inside the switch making contact where it should not. This would not be a short strictly speaking.

The lights going out could also be a poor fuse contact that heats up and 'opens'. So replace the headlight fuse and check the fuse clips are clean and grip the fuse securely. As stated this won't cause the lights to stay on. Likely both problems are in the switch.

Mike, thanks for taking the time to comment.

datsunmike wrote:

levigideon wrote: Today it happened again, but after I shut everything off, my dash lights all stayed on, no matter what I did with the headlight switch.

No fuse is going to power the dash lights when the switch is off. This is likely a failure in the headlight switch.

If you are careful you can pry back the folded metal tabs that close the switch to hold the parts in. Have a care as you may only get one chance. Bending these tabs more than once may snap them off. You can take out the sliding parts and the brass contacts and clean them. May even be something in there that's broken like a spring.

To remove the switch unplug it first. Pull switch out fully. Grip the brass stem tightly with needle nose pliers and at the same time push inward on the knob and turn to release it. Now loosen the nut on the front of the dash and push the switch through and retrieve.



A short is a path around a load to ground and would either blow a fuse, which is what they are supposed to do, or melt a wire starting a fire. An open (or bad) connection would cause the lights to go out. This could be a dirty or worn contact, often intermittent. The dash lights staying on could be something loose/broken inside the switch making contact where it should not. This would not be a short strictly speaking.

The lights going out could also be a poor fuse contact that heats up and 'opens'. So replace the headlight fuse and check the fuse clips are clean and grip the fuse securely. As stated this won't cause the lights to stay on. Likely both problems are in the switch.

Thanks for this Mike. Took a closer look tonight.

Flipped the headlights on... waited for them to flicker off. Tapped the relay once, nothing. Tapped it again... One headlight and the running lights came on. Wiggled the other headlight socket, it came on. The switch got warm pretty quick. So I decided to dismantle it and see what the skinny was with it.

Pretty corroded around the sides of the casing, but the connectors were all in good shape. A little gunk and dirt here and there, but all fairly clean. Decided to clean it out anyways. Hooked it back up, not so hot anymore, nothing flickered off.

Seems it was a combo of both the relay and the switch. I'll probably just swap out the relay with a bosch that we've got laying around.

Lesson learned: You can never clean connectors enough. Time for another vinegar scrub. Gotta see if I can drive this car to Bellingham next week.

Vinegar works good. So does a pink pencil eraser. Just put it on there, and rub it down to brass again. Works amazing on computer stuff too. I use it on my gauge clusters where the light sockets go. Nothing harsh, nothing wet, cleans it. no finger oil left on there to eat it away... Good shit.

I have always used a razor blade.

Forgot the relay... but the relay can't keep the dash lights on. If you had it (headlamp switch) out sometimes just messing with it will fix it.