Need advice with parasitic battery drain

[Tanaga]

I've spent hours reading the histories on this subject but still don't have it figured out yet. I know there are a lot of very smart people on here that can point me in the right direction. I have a 1984 M1028 that the state forestry department did a Roscommon 12 volt conversion on it. It now only has one alternator on the passengers side. I have 2 new Optima red top batteries less than 3 months old (12.8 volts at rest on both). I have followed the advice on here and on YouTube on how to track down the problem. I've attached a volt meter between the negative battery post and the negative terminal on the front battery. Then removed all the fuses one at a time and found nothing. Then I started disconecting other stuff like the glow plug wires on the positive bus bar, removed all wires from the starter relay, and removed the red wire from the back of the alternator and it still have a 0.15 draw. It should be no more than .02 amps, so I've heard. I have no radio. It's all stock except the 12 volt conversion. After all this testing I checked the voltage of the batteries and it looks like only the rear battery is draining. I would have to double check this again though. Is there another fuse box besides the one by the emergency brake? What else can or should I check?

Thanks!

 

[tobyS]

Every time I drain one battery I have left the light switch on so I can use turn signals. Once it was low speed on the heater blower but the lights are my problem usually.

 

[GunnyM1009]

I have never been good at tracking drain. The last time I had it I installed a battery cut off switch on the draining battery. I realize thats no help to your problem but it works if you can't figure it out.

 

[Warthog]

Disconnect the two-pin exciter plug on the alternator. Many times the alternator is the problem.

 

[87J]

I agree with warthog I have seen many alternators be the problem. Unless it's only a 1 wire alternator you need to disconnect everything to confirm. Other than that keep unhooking wires until you find it, possibly a small short on the starter solenoid... Just to confirm your not hooking the meter on the negative that ties the 2 batteries together are you? If you are 1 of your batteries could be bad causing the drain.

 

[Tanaga]

Every time I drain one battery I have left the light switch on so I can use turn signals. Once it was low speed on the heater blower but the lights are my problem usually.

Isnt the headlights and the heater fused? As soon as I pulled that fuse I would have found the problem.

 

[Tanaga]

Disconnect the two-pin exciter plug on the alternator. Many times the alternator is the problem.

I've completly disconected the alternator and there's still a draw so it has to be something else. Actually since the 12 volt conversion, the plug is not being used. Just a red wire and a ground.

 

[Tanaga]

I agree with warthog I have seen many alternators be the problem. Unless it's only a 1 wire alternator you need to disconnect everything to confirm. Other than that keep unhooking wires until you find it, possibly a small short on the starter solenoid... Just to confirm your not hooking the meter on the negative that ties the 2 batteries together are you? If you are 1 of your batteries could be bad causing the drain.

I will ill try disconnected the starter next. That's a good idea.

Since the 12 volt conversion, my batteries are wired in parallel not series. Both grounds on the batteries are bolted to the negative bus bar, same as the positives. So I don't think it matters which battery I test, does it? I left the batteries disconected last night and not on any kind of charger. This morning one was 12.81 and the other 12.79.

 

[87J]

I will ill try disconnected the starter next. That's a good idea.

Since the 12 volt conversion, my batteries are wired in parallel not series. Both grounds on the batteries are bolted to the negative bus bar, same as the positives. So I don't think it matters which battery I test, does it? I left the batteries disconected last night and not on any kind of charger. This morning one was 12.81 and the other 12.79.

It would matter in this case because testing amp draw on either of those 2 negative leads is technically testing on a connection between the batteries.
Usually when batteries are in parallel the negatives and positives connect at the batteries to tie them together and then 1 lead from each will feed the truck giving you one path for each. There's nothing wrong with the way yours is set up but testing this way you could be seeing a minor amp draw between the batteries. Its unlikely 1 is bad but food for thought.

 

[MarcusOReallyus]

So they each have a separate ground cable going to different points?

If so, you need to disconnect BOTH of them to find the draw. If you only disconnect one, the other will supply current to your parasite, and you will be looking at the disconnected one in vain.

You may have been chasing your tail.

 

[Artisan]

...and if battery's are completely disconnected from Everything they hold a charge?

I had a battery 2 weeks ago that had some kind of parasite drag, or so
I assumed. I charged the battery and let it sit overnight, in the AM
it was down ...new battery and all is well.

 

[Tanaga]

So they each have a separate ground cable going to different points?

If so, you need to disconnect BOTH of them to find the draw. If you only disconnect one, the other will supply current to your parasite, and you will be looking at the disconnected one in vain.

You may have been chasing your tail.

The front battery negative cable has a small wire spliced in that grounds to the radiator support. I've seen this before on other vehicles. The big negative cable from the front battery goes to the negative bus bar. The rear battery negative cable also goes to the negative bus bar. Then there's a short cable that connects the negative bus bar to the rear on the intake manifold.

So so how do I do this test if I disconnect both batteries? The videos I've seen only show how do test on vehicles with one battery.

 

[Tanaga]

...and if battery's are completely disconnected from Everything they hold a charge?

I had a battery 2 weeks ago that had some kind of parasite drag, or so
I assumed. I charged the battery and let it sit overnight, in the AM
it was down ...new battery and all is well.

Yes, batteries hold a charge. I've had the batteries disconnected and not on any charger for 32 or so hours. It even got below freezing last night. One has 12.80 volts and one has 12.82 volts.

 

[zebedee]

The only way I have ever found a drain was to remove the batteries altogether, connect the battery cables together -ve to +ve at each battery, pull all the fuses then meter across each fuse holder to see which circuit has continuity - which they shouldn't if everything is "off".
Once you have found which circuit has the problem - unhook the battery cables and meter each half of the fuse to either battery cable end - that will cut your searching of that circuit in half. After that, you are tracing the circuit for chaffed wires or bad components.

 

[Tanaga]

The only way I have ever found a drain was to remove the batteries altogether, connect the battery cables together -ve to +ve at each battery, pull all the fuses then meter across each fuse holder to see which circuit has continuity - which they shouldn't if everything is "off".
Once you have found which circuit has the problem - unhook the battery cables and meter each half of the fuse to either battery cable end - that will cut your searching of that circuit in half. After that, you are tracing the circuit for chaffed wires or bad components.

That's a good idea. Could I also use just one battery, somehow attaching 2 + cables on one post and using a C-clamp attach the 2 - cables together and run my amp meter between the - battery post and the 2 neg cables that are clamped together?

 

[zebedee]

That's a good idea. Could I also use just one battery, somehow attaching 2 + cables on one post and using a C-clamp attach the 2 - cables together and run my amp meter between the - battery post and the 2 neg cables that are clamped together?

NO, you don't need a battery for this test. You are measuring continuity. You are looking for 'clean' circuits that have infinite resistance (1) because they should be switched off and not running to ground (the -ve side) which is the drain you are looking for. Any circuits that have SOME resistance means that it will pull from the battery even when switched off and hence draining your batteries.
It's like a dimmer switch for room lights that does not go all the way off when you go to bed but leaves a little glow - as opposed to a switch that turns off the lights properly.

 

[Tanaga]

I think I got it narrowed down to the alternator. I removed it and am going to have it checked. Will let you know the verdict.

 

[rustystud]

I thought you said you checked the alternator ? If it is the alternator it is probably the diode pack. The diodes go bad and allow a "back flow" of current. Very common problem with GM alternators.

 

[MarcusOReallyus]

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[rustystud]

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