I'm Not A Wizard - Electric Problems

78 CJ5 - bought just a few weeks ago, and I am cleaning it up and trying to fix what's wrong with it, to give to my son to drive. It has a Chevy 305 in it, needs a water pump and radiator and a new top and some rust repair and a new front driveshaft and and and...
But what I'm working on right now is getting the electrics working. Heat and defrost were FUBAR, but they work now. The next project (and topic here) is the lighting system. I had an issue where the parking lights were on all the time, even if the switch was off. I had to disconnect the battery to get them to go off. I suspected a bad ground, and sure enough discovered that the switch wasn't properly grounded (at least there was a black wire hanging off in space) I grounded the switch, and now the two parking lights in the front turn off, and the right rear turns off, but the left rear still shines.
What could possibly cause that? I'm all ears boys!
New member here -nice to meet you all!

 

is it another bad ground? on the light itself this time?

you're officially in the rabbit hole now...

 

Do the brake lights work? Does the brake pedal return fully? I'm thinking, if it stays slightly depressed, and the right side brake light is burned out, you may have fixed one problem but now have a different problem that looks like the same problem.

If that doesn't do it I'd pull every bulb, make sure the sockets and contacts are clean and the bulb is installed correctly.

I saw a problem once where a broken filament was laying on the other filament in a tail light and back feeding to the dash bulbs.
Every time the brake pedal was stepped on the dash lights came on.
The mechanic working on it eventually pulled the gauge cluster out before he found the bad bulb in the tail light.

 

Welcome from SoWeGa.

 

Welcome from France. We have goos specialist in electric"ctricity on this forum. I myself had some surprises.
It takes time to checks all and it needs lot of logic. Cleaning, testing use a device to check independent from your Jeep.
I generally use a light with a small battery to see what goes were.
I also used a sound signal (buzzer) to hear if there is a contact, when I cannot see. Small tricks, but useful. IMO.

 

May or may not solve your case, but parking and indicator lights often get weird when the bulbs and receptacles need cleaning, and better grounding. Due to their multiple functions, current can feed back through the bulbs into secondary pathways.

Won't hurt, and might help, to do a careful cleaning of each bulb and socket before going any further, and be sure each unit is effectively grounded.

 

Could be. I'll dig back into it tonight. It's a real hack job. Someone put a GM tilt column in, and butchered the wiring under the dash. Every time I look at it, I'm tempted to tear it all out and rewire the whole thing. But I'm also determined to keep this simple - to just fix what's broken. I'll check all the grounds, sockets, etc tonight.

 

Welcome from Idaho!

 

Welcome from Boston!

How much effort do you want to make to understand this? As mentioned, loss of grounds can cause unexpected behavior from these circuits. I would look at it by measuring (disconnect the wire and trace where the current comes from) combined with following the factory wiring diagram. I would make sure I was looking at the correct diagram for 1978. There is a copy of the TSM here Jeep® Parts Manuals online free to read and download. I would photocopy the diagrams, blow them up, and trace the circuits in colored pencil as I traced them. Possible you could figure it out by just looking at the diagram, but that seems both uncertain and inefficient. Unlikely that anyone has a sufficiently detailed mental model of these circuits to tell you what's happening, without some significant effort.

These Jeeps came with the GM column from the factory, and optionally a tilt column. I understand that the factory tilt column is a desirable upgrade. Lacking a factory column, your PO may have installed a tilt column from a passenger car.

 

I had a similar issue when I acquired my jeep last year. Engine ran, but none of the lights worked. I ended up pulling every single wire out of the Jeep and starting from scratch. I honestly think it took less time than trying to trace all the wires and separately fix each problem. And then end result is much cleaner than what was there before. I pulled all of this out, and the engine still ran:

 

i wanna go through and replace all th wires, most are likely cracked

 

Maybe that's the best thing to do. I have a 72 240Z that I'm re-wiring. I guess I could steal some stuff from that project.

 

Suggest before you decide to rewire, trace the remaining live tail light back to where the power is coming from. The indicators, brake lights and hazards are the same filament, and all go through the turn signal switch in the column. This is where the indicators are prioritized over the brake lights for that side, and where hazard signal is directed to all four corners. A '78 is pretty new in terms of old cars generally, and the wire is probably fine. Really old Jeeps can have cloth-covered rubber wire that's falling apart, but vinyl-covered wire (PVC insulation) in a '78 is probably ok.

I see this on these forums all the time - the wiring seems so overwhelming that owners think they have to rip it all out and start over. The marketing of companies like "Painless" suggests that their products are an easy way out of what looks like a confusing mess. I say - it's easy. This is all 12V DC - no shock hazard - and it all conforms to the constant form of Ohm's law, just like water in a pipe. Take it one circuit at a time, and tidy the mess as you go.