Datsun 720, Key off, Battery/Charge light on.

[oversteer_ms]

New to Ratsun community.

 

Im currently having issues with my 1984 Datsun 720 4x4.

 

The battery/charge light is on with the key off. It shuts off when I turn the key to the on position. But after a few days it will drain the battery down a little and you all know how lovely the z starters are with a weak battery.

 

I am charging a full 14.3 volts at idle. The battery is brand new. 875CCA. Getting a 0.4xx Amp parasitic draw.

 

I have been racking my brain with this issue for a week now. When I pull the battery/charge bulb out from the back of the cluster and i put it back in, it makes the door beeping noise at the left kick panel.

 

Any input will be greatly appreciated.

 

Thanks in advance,

Austin Johnson

Oversteer Motorsports

[DanielC]

Disconnect the alternator wires, the small wires that plug into the alternator, and the big positive wire too. Be careful with the big positive wire, when the battery is hooked up, it is hot all the time.

Did the amp draw go away?

If yes, suspect the alternator. Something in the alternator may be back feeding the alternator charge light.

If no, Pull all the fuses, remembering where they go. Use a egg carton to hold them, is one way to keep them in order.

See if that makes the amp draw go away.

 

The charge light normally is turned turned on by the ignition switch applying battery voltage to one side of it, and before the engine starts, it is grounded by the alternator. When the engine starts, the alternator applies 12 volts to the "grounded" side of the charge light. so the light goes out. The alternator should not feed battery voltage back to the charge light without the alternator turning.

[oversteer_ms]

Thanks for the reply. I have pulled all the wires off the alternator and the light is still on with the key off. When I started it with the wires all unplugged from the alternator I didnt have a charge light like I should have.

 

Its the damndest issue. I know its going to be something simple too.

 

I have also pulled the fuses as well. All one by one and it still doesnt go out.

[DanielC]

Time to get an electrical schematic, and see if you can figure something out.

 

This sounds like it could possibly be two wires that normally insulated from each other connecting to each other. a condition often called a short circuit, but this does not short to ground.

My understanding of the charge light function on an Ir alternator system is this. The alternator side of the charge light is just a wire connecting the charge light to the "L" terminal on the alternator. Nothing else. Unplugging the small connector on the alternator should have made that wire a open circuit.

[oversteer_ms]

I have mapped out the entire charging system diagram and I cant figure out what the issue is...

 

 

 

 

[oversteer_ms]

I have searched for flow charts and what not but nothing related to this issue. The above schematics are from my Mitchell On Demand account.

[ggzilla]

Not a simple problem. Not caused by alternator.

 

Trace where the 12v is coming fom when key is out.