Weird power issues

[converted_to_datsun]

I have a 1979 620 and started having some strange electrical issues. I'll try to be as clear as I can but I'm pretty stumped. One of the issues is the starter won't work when the truck is off but will engage if running which I know shouldn't be done but it does work. The other issue that seems to be related to the same problem is hard to explain so bear with me... When the lights are on and the radio is on the lights dim and the radio shuts off completely if I turn on the brights. The brights aren't lit up tho. Sometimes the radio shuts off at idle too. I've cleaned all the connections at the battery and the starter. It seems to be running completely from the alternator when running. If the truck is off and you turn on the key all the lights come on and everything works but the radio and light issue is there.

 

Oh and the reason I know the starter and the other issues are related is it happened before and once the short stopped happening the starter also worked just fine again.

 

Any ideas? I'm pretty lost

[Draker]

Have you checked to see if your battery is any good? Sounds like it's time for a new one.

[converted_to_datsun]

It has 12 volts. I can get it tested to be sure tomorrow tho. But the lights and the radio? Would that be battery?

[Dat Lurka]

Gremlins.

[converted_to_datsun]

No joke haha my dogs name is gizmo... Haha

[Dat Lurka]

Lol

Go somewhere and have the battery and alt tested.

[converted_to_datsun]

First on my list tomorrow. The alt was new from the po and Skib helped me test it last time and it tested good. Batter might be the weak link but seems to have plenty of juice... I hate wires sometimes

[Laecaon]

I love wires, but hard to diagnose over the internets. A lot easier in person.

[Dat Lurka]

Also sounds like a grounding problem. Never hurts to add bigger better wires from bat to ground, alt to bat, bat to starter, etc.

[converted_to_datsun]

Well if you have time on your day off and I haven't figured it out. I might need a fresh perspective.

 

There's already an extra ground from the battery to the starter. But not sure where to start with the rest. The radio shutting off has me scratching my head

[Laecaon]

So this problem is intermittent?

[converted_to_datsun]

It sticks around for about a day then goes away completely till it pops up again. Second time it's happened and last time was about 2 weeks ago

[wayno]

If you hit the starter while the engine is running, how do you know the starter is actually running, and not just slamming the moving flywheel?

Check the main cable from the battery to the starter, also check the actual post cable connection, same with the ground cable.

Modern radios shut off when they get down to a certain power level, an example would be that the radio will work till you turn on the headlights, and will come back on when the lights are shut off.

Another example would be that the turn signals/radio work when the engine is at higher RPMs, but when you drop to an idle things quit working, check everything, cables, alt, battery, voltage regulator, fuses, ect.

[converted_to_datsun]

My truck is a 79 so the alt is internally regulated. I've cleaned all the connections I can think of connected to the starter. Al the battery cables there is plenty of juice coming from the alt. I guess I can check the alt wires too. Problem is the starter worked perfect again after it stopped last time. So I'm thinking some how it's connected. I'm starting to think it's the battery the more it think but last time I checked it and it seemed fine from what we could test

[DATN510]

Get a diagram of you wiring system,

Follow the wires that may cause the problem, could be a wire that's just barley connected.

I've had this problem before.

[converted_to_datsun]

It's worse now... Seems like everything is running off alt mainly and draining the battery too. At idle my whispers stopped half way up the windshield today. Can the alt power the motor but not power the battery if there's a bad ground?

[banzai510(hainz)]

Your got a volt meter?????????

and test light.???????

 

ck and clean fuses

clean battery terminal or get new cables.

reseat the key connection

[converted_to_datsun]

Already done all that. I completely redid my fuse box so no corrosion there. Haven't done the key but does that controls my battery power? Seems to be a different problem than the key

[banzai510(hainz)]

yeah Im not a real 620 expert I know 510s more.

unless you think you got s major intermittan short soemwhere thsat just loads downs the systm

Biggest power draw is the starter.

[datzenmike]

Unplug your fuse box and remove from the dash. Pull the fuses and soak in a mixture of full strength vinegar and lemon juice overnight. Replace with new fuses and install.

[converted_to_datsun]

I just did that mike. I have a fresh fuse box, it's been soaked and part of the harness replaced

[LenRobertson]

When I first got my '79 200SX it had an intermittent electrical problem that drove me crazy. It turned out to be a bad fusible link. It hadn't burned out and bubbled the outer insulation like they are supposed to. The insulation looked just fine, but internally it must have been almost broken in two. Probably not what your problem is, but I thought I'd mention it. I looked at the wiring diagram for a '79 620 and it shows at least one fusible link.

 

Now I have to go out any deal with my own electrical weirdness on my 510. After I came in last night I came up with "The Answer" to my problem. Feeling pretty good I know what's wrong - until I test my theory on the 510 and find out it doesn't help at all.

 

Len

[Draker]

It's important to know that because a battery has 12v doesn't mean it's good. It's the amperage that really matters. Have the battery load tested. Does it have enough power to start the engine?

[D52E]

I haven't had a starter issue but I highly recommend starting with a baseline of checking your battery and alternator output.

 

Idid have a similar issue with lights dimming and then getting brighter. My concern turned out to be a bad ground to the body. My battery ground had a good connection to the engine block but the connection from engine block to body was bad so my lights would dim and flicker depending on throttle input. My throttle cable was actually providing an alternate ground path.

 

Perhaps you can connect a jumper cable from battery negative to body or chassis and see if there is an improvement? Maybe even use a clamp on battery jumper cable for a temporary trial?

[converted_to_datsun]

Alternator is fine. But the freaken short went away again... It starts and the radio stays on again. Gonna get the battery tested later