Won’t hold power.

[cruiserboy14]

I’m having trouble figuring out an electrical problem. I have a 77 us model 40. My battery doesn’t seem to hold a charge long. I have it on a trickle charger when I’m not using it. I have replaced the battery, but no change. I suspect my alternator, voltage regulator or it may be some wiring. I have taken off the terminals on the battery and it seems to run well without and it has 13.75 volts across the cables while disconnected. I haven’t trouble shot something like this before, so I’m looking for any help. I do have a wiring diagram, and to my knowledge everything is oem, except som Po wiring.

 

[pb4ugo]

13.75 volts indicates the alt is probably charging. Disconnect the batt cables and check the batt voltage and write it down. Now reconnect the positive cable to the batt. Now using your voltmeter put the red lead to the negative batt cable and the blk lead to the negative batt terminal. If the voltage is less than the earlier recorded batt voltage means you have something drawing voltage. lIf the voltage is the same would be an indication there's no short or draw. You can track down a circuit by pulling individuals fuses and watch the voltmeter reading. You might end up disconnecting the alt to see if it's the problem too.

 

[cruiserboy14]

13.75 volts indicates the alt is probably charging. Disconnect the batt cables and check the batt voltage and write it down. Now reconnect the positive cable to the batt. Now using your voltmeter put the red lead to the negative batt cable and the blk lead to the negative batt terminal. If the voltage is less than the earlier recorded batt voltage means you have something drawing voltage. lIf the voltage is the same would be an indication there's no short or draw. You can track down a circuit by pulling individuals fuses and watch the voltmeter reading. You might end up disconnecting the alt to see if it's the problem too.

Thank you for that. Do you do this when it’s running or after shutting it down?

 

[pb4ugo]

Turned off. It's a basic test.

 

[cruiserboy14]

Ok I drove it to work today. It worked ok. When I came home I tested it. Battery disconnected read 12.86 volts. Positive connected, reading threw ground it read 2.84 volts. So that should mean I have a draw somewhere that’s 2.84 volts?!

 

[pb4ugo]

I'm not sure that could be right. It indicates a 10 volt draw. That would be pretty extreme.
12.86-2.84=10.02. You might want to test again. Be sure you have good connections with the probes. Red lead on the disconnected neg cable and black lead on the negative batt terminal, and clean cable ends and posts.

 

[fyton2v]

Pretty obvious, but did you rule out accessories? Some phone chargers, 12v to 110v outlets, etc can be drawing power constantly, even when not being used. The cigarette lighter and the little outlet in the glove box (if you have one) are getting 12v from the battery when the ignition is off.

 

[cruiserboy14]

@fyton2v I don’t have any accessories yet. Just what it came with from factory

@pb4ugo I checked the battery again (12.80) and I’ve re verified the voltage from the negative terminal to the negative cable, it’s 1.79 today. I tried switching around Leads, I tried to isolate the loss by disconnecting fuses, all still the same.
I also cleaned the cables and terminals.

 

[1969FJ]

 

[pb4ugo]

You might try the same test with alt disconnected. They can fail by drawing power too. You can do the same test with amps like in the referenced video. Your alt wiring looks unique. Be careful, the big wire is hot if the batt is still connected while removing it.

 

[cruiserboy14]

@pb4ugo I’ll try that. I’ve always suspected that the “special wiring” was a potential issue.. I’ll try with my alt disconnected. Thank you.

 

[cruiserboy14]

Ok, progress. Battery:12.83, battery to ground: 2.83, battery to ground with alt disconnected: .27!

 

[cruiserboy14]

I’m leaning twards my alternator being bad. I think I’m going to source mine from cityracer. But before I replace it, I think it will be wise to sort out the oem wiring. I may possibly try and redo that section with wire from @Coolerman. That way I know I’m putting good parts into good wires.

 

[ToyotaMatt]

did you hook up the missing wire to the Vacant tab on voltage regulator yet Seth ?


- there is NO other way to be 100% sure except do exactly as you see below ,

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- if you do discover you

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- you DO NOT Guess or speculate on the topic of your thread , you confirm and verify , that will provide you a concrete diagnoses all by it self if you allow it to ...



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THIS IS THE WAY ........


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[45Dougal]

1) How quickly does your battery discharge?
You can then work out roughly how many amps are being drawn. I.e. If you have a 100Amp-Hour battery and it's flat after 10 hours then you're losing 10Amps.
2) Remove all your fuses. Does it still loose a charge?

I think the test outlined above was supposed to be testing AMPS not volts, but without knowing what meter you have it might not be the best way.

 

[hobbes]

Probably not your issue, but while you’re at it, the alternator should ground thru the mounting bracket. Make sure it is. Corrosion can build up between the bracket and engine. The engine then grounds via the starter strap.

I run a ground wire from my negative battery post to the alternator bracket as insurance per Coolerman’s recommendation. So I essentially have 2 grounding straps to my engine (starter, alternator bracket). Bad alternator grounding does funny things.

Again, I doubt it's your issue, but if you're refreshing the system it's something to verify

 

[cruiserboy14]

thanks to @Coolerman I’ve replaced my wiring going from my alternator to my voltage regulator. It looks and works great. New connectors and all. I let it sit for 4 days with the alternator disconnected and it seems to have leveled out. Dropping .20 volts. After re-connecting the alternator it seemed to level out. It also started up without the charger. So an improvement! I still believe i have a draw but possibly not as bad.
Also I was routing under the glove box and came across this connector not attached. It’s in the last photo. Anyone know that this goes too?