0.75 Amp Parasitic Draw

I have had an annoying parasitic draw as long as I have had the car. The ground cut-off switch has allowed me to live with it but now I'm trying to run that down as I want to drive the car more and do not want to raise the hood every time I stop/start.

I started at the battery. I have the old 3 positive cable set-up and without the Maxi fuse box.

For my baseline I ran a multimeter in series with the ground on the negative terminal, and the plus wire on the cam cover ground lug. RESULT 0.75 amp AC (about 1 amp DC).

First I pulled the two positive cables that run to the electrical board terminal. RESULT 0.74 amp AC. I replaced the two positive cables.

Second I pulled positive cable to the alternator (at the alternator lug). RESULT 0.74 amp AC. I replaced that cable.

Third I pulled the three wire connector on the alternator. RESULT 0.02 amp AC.

What to test next?

The three wire terminals are battery power for voltage reading, switched power from ignition to turn the regulator on, and ground for battery warning light.

I doubt it is the ground wire because the battery light does not come on. The battery drains when the ignition is off, so likely not switched power. That leaves the battery wire.

How to test it? I am thinking I hook my battery charger (12v, 2a) positive cable to the battery post on the three wire socket, then the negative cable in series with my multimer, hooked to the alternator body. If there is a leak in the alternator, that should catch it (I hope).

 

Thanks, but my problem does not seem to be on any fused line as disconnecting the entire fuse panel (two + cables to terminal-see the last pic I posted) only resulted in a 0.01 amp drop in the parasitic draw. Maybe I am not thinking about that correctly?

 

Thanks for the feedback. My charger is 30 years old. I think it will give a load.

I completely disconnected the alternator from the car electric system, and disconnected the negative car battery terminal via the switch. I disconnected both the alternator terminal lug and the three wire connector.

I then ran the battery charger 12v/6a positive cable to both the alternator terminal lug and the S terminal on the alternator three wire socket to simulates the unswitched battery power to the alternator.

Then I ran the battery charge negative cable to the tester positive cable.

Then I ran the tester negative cable to the alternator body.

RESULT: 0.74 amps!

My guess is a bad diode in the alternator causing the leak.

 

My understanding is an AC meter can test dc amps but not vice/versa. I also had the same concern you did so tested the meter with an old school analog meter and got 1 amp which I think is a close conversion ac to dc.

Gonna try the diode test function next.

 

See the pics in my first post above. Two of the cables go to the terminal behind the fuse board, and the third goes to the starter/alternator posts. The sensing line S terminal runs to the battery but I am not sure how. I think it may pull off the starter lug. I did not pull it all apart.

Hanging it up for the night. I do not want to crawl under the car again... Will post an update on the diode test tomorrow and will run the same test with the old school ammeter.

 

FBB thank you for chiming in. Your help is always welcome. Perhaps you missed my first post, it was a bit long. I started with the basic amp meter test method (no battery charger).

The 456 is unique in that it has 3 main power branches coming off the positive battery terminal. As usual, a fat one to the starter. This one continues to the alternator output post. The other two are fat lines running to a terminal post behind the fuse board (see diagram pics in the first post). This powers the rest of the car. I believe this system was replaced after only few production years with the MAXI fuse box so you may not be familiar with it.

The problem with your method (pulling fuses) is that it presumes a voltage leak is BEHIND a fuse. But what if the leak is NOT behind a fuse? I do not believe your method will pick that up.

Armed with that thought, and the unique three branch nature of the 456 electrical system, I started at the battery terminal and removed one of the three branches at a time. The first two (leading to the power terminal behind the fuse board) yielded only a 0.01 drop in parasitic draw. By doing that, I believe I have eliminated any problem on (and downstream of) the fuse board. This left only the third branch of the starter/alternator.

Bad alternator diodes are often the cause of voltage leaks. So I decided to test the alternator in isolation by removing the battery line and the 3 pin connector. In order to conduct my test I need 12v power supply. Enter the 30 year-old battery charger. So I am really bench testing the alternator on the car, as removing it is quite a PITA.

Again, I appreciate your feedback and hope you can appreciate my method, while not your method, I still a viable test.

 

Qavion, thanks for the feedback.

That is my set up to bench test the alternator. I do not follow your reasoning on two diodes have to go bad for a voltage leak. My understanding is a diode is a one-way valve. An alternator is AC (two ways) and the diode only lets one direction flow turning AC into DC. If the diode is bad, won't battery current flow out to ground? But hey, I'm not a double e.

But here are a bunch of videos checking alternators for bad diodes in search of parasitic draw. So my crowdsource instinct tells me there is something to it, even if I do not fully understand it.

https://www.google.com/search?sxsrf=APwXEddRw318fYyfr7T9oUUDxc1dM62O_Q:1686971367512&q=bad+diode+in+alternator+drain+battery&tbm=vid&sa=X&ved=2ahUKEwjS9eyIqsn_AhWWJ0QIHUnhAVwQ0pQJegQIDBAB&biw=1280&bih=646&dpr=1.5.

 

I replicated the parasitic draw test with my old school analog DC amp meter. I want to be sure my modern AC multimeter ammeter was not leading me astray.

So I hooked everything back up with the battery negative cut-off switch open (off) and retested. Sure enough, 1 amp draw.

BUT WAIT!!! When I went to take a picture, back to zero. WTF???? Checked all connections, reset, etc. and again, 1 amp.

Go to take picture and ZERO. Ok, something is going on. Turns out the current lasts for about six seconds, then goes to zero (like I am draining a capacitor).

Here is a video I made. Note the needle moves from zero to one when I connect the test lead to the negative battery terminal. Then about six seconds later the needle abruptly drops to zero, all test leads still connected.

 

Thanks FBB.

 

I have a light tester I tried as well. Same result. A flash of light then it goes out. Just about four seconds faster than the analog ammeter.

Gonna go grab some breakfast at the golf clubhouse next door and ponder my next step...

 

Kinda where I am at right now...