Hmmm - Bad Light Switch Circuit Breaker?

1956 CJ5, F134, 6v system...

Earlier today I got the horn working on my CJ5 - the last electrical thing needing my attention. Tonight, my neighbor and I are "aiming" the headlights and we take a spin around the neighborhood to test our work. Pulling back into the driveway after about 5 minutes of driving at various speeds, rpms, etc ALL the lights suddenly go out/fail. But the horn still works.

I figure it's a bad circuit breaker on the switch so I shut off the jeep, pack up my tools and say goodnight to my neighbor - maybe 3-5 minutes go by. I climb back in the jeep start her up to pull into the garage and for grins I pull on the light switch and everything is working again (headlights hi & lo, cluster lights, tail/brake lights, parking lights all functioning as they should).

Now I'm thinking that the breaker didn't go bad. Maybe it simply got hot enough to shut off and the 3-5 minutes allowed it to cool down enough to function again. Can they do this? I didn't go anywhere after pulling into the garage so the jeep only ran for a couple minutes once things were functioning again.

Maybe I've got a bad ground that reared it's head for the first time this evening. I've driven the jeep extensively prior to tonight and never had the lights all go off, but that was prior to fixing the horn.

Before I go chasing wires and replace the switch, is there anything else that comes to mind?

For background, the majority of my wiring harness is the cloth insulated type and is original to the jeep. I've replaced some wires and wrapped/insulated others in an effort to get everything working. I'm putting off a complete re-wiring/new harness as long as I'm able as funds are tight right now.

I'm going to drive it around the neighborhood a bunch tomorrow during the day when its safer to see if I can repeat the failure.

Thoughts on what might have failed, then started working again, are appreciated. Thanks as always!

 

Wonder what that circuit breaker is for? See FSM for details. You had a short and the breaker kept the most important lights working. It did cool and reset. It will trip again until the short is corrected. Hope that helps.

 

I would say an intermittent bad earth/ground but saying that would have taken out all the lights seems like a stretch.
Then again the CJ5 wiring harness is 9/10ths less complicated than more modern vehicles.

Definitely check everything--my guess is corroded ground(s).

 

That is exactly how the circuit breaker is supposed to work, if the wiring shorts or is overloaded.

At the same time, it is possible the circuit breaker itself may be "weak" and tripping prematurely.

 

Could possibly be this as they don't last for ever.

 

You can get a ballpark measurement of whether the CB should be popping based on what your multimeter says. Measure from the light side of the CB to ground and record the readings in ohms. Then, by Ohm's law, V=IR or equivalently I=V/R. So if you measure near zero, say 1/2 ohm, that's 12/0.5 = 24 amps. If your CB is rated at, for example, 20 amps, at least you can eliminate the CB as your fault until you find the short in the wiring.

If you make a measurement of these kind of low resistances, touch the leads together, note the resistance of the leads and the meter works, and subtract that from your measurement.

Really, if you measure anything but open (or near-open, like few megaohms,) you have a short somewhere. "Chasing wires" as you call it, is the right way to approach this. Divide and conquer. The CJ wiring is really simple - just disconnect and test each circuit resistance to ground until you find the short.

The old cloth-cover wires are actually cloth over rubber insulation, as I recall, and the rubber will deteriorate by exposure to sun, air and smog. If the cloth cover wears away or frays, likely the rubber fails soon after and you could have a short. IMO this is a good reason to buy a replacement harness from Walcks. These harnesses use period-appearing wire, which I believe is cloth over plastic (PVC), which is much more durable. With plastic sheathed wire, I'd just fix the offending wires, but with the old rubber-insulated wire, replacement is likely the prudent course.

 

Thanks guys - I'd never had the breaker reset over the years when I had my 3A. It would just blow and stay out when I'd do something dumb. Thats what kinda threw me this time around with my CJ5 as nothing had changed, except for getting the horn going. I'll start there looking for shorts and/or ground issues and work my way through the rest of the systems. A Walcks harness is on the "future" list for sure. Thanks again.