M1008 Killing REAR battery?

[rose jackets67]

First post here - I've done a LOT of searching with no luck.

A little background - I'm a LEO in Georgia, and this spring I bought a 1985 m1008 that had previously belonged to a neighboring fire dept. I drove the truck daily for about 3 months until it starting acting up.

I went to leave for work one morning, and the glow plug 'wait' light stayed on extra long. I knew what that meant before I hit the key. Yep, battery(s) dead. So i jump it and head to work.

I replaced both old mismatched batterys with 1000amp units from the local auto parts store. Same problem. Front battery stays at around 12.6 volts when the truck is off. Rear battery goes to zero in a matter of hours. As far as I can tell, there is a pretty serious drain on the rear battery, BUT, my understanding is that all 12v accessories are run off of the front battery. What could be killing the rear?

When I first got the truck, I stripped out all of the additional aftermarked items added by the fire dept as well as the wiring to them. I drove the truck for another two months without any issues, so I don't think I caused any shorts then.

Both alternators put out proper voltage at their lugs (14.1-14.3 volts), but with the truck running the rear battery never climbs above around 13 volts.

Otherwise, the truck is wonderful. Currently it has 4.10 geared axles under it and is a pleasure to drive. Generally speaking the truck stops good, runs good, hardly leaks any oil, leaks no trans fluid or gear oil and goes like hell in the mud.

The only issues aside from the power draw are the right front high beam is dead (wiring issue - known good lamp installed and it's still dead), and neither of the Gen lights have ever illuminated.

Any assistance would be greatly appreciated. I bought this truck with the intention of installing a 4 cylinder B-series Cummins, but right now I can't even move it around the shop!

 

[rose jackets67]

Yes, it's red

I'm thinking Desert Tan before it's all said and done. We'll see.

 

[wallew]

rj 67,

I'm guessing mind you. But you MIGHT be having one of two problems.

1) Alt resistor could be bad?

2) How do the battery cables look?

I recently replaced both alternators in my M1009 and then all the battery cables and MOST of my charging problems disappeared. This was after I put the truck BACK to 24v, which also resolved several issues with starting.

Also, you did not say if the truck is still 24v or has been converted to 12v. That info alone will help everyone here.

Given that it DID work and then stopped, I guess bad alternator. But like I said, I'M GUESSING.

 

[rose jackets67]

Truck is still 24 volts.

When the truck is running, both alternators give 14 volts at the + side. I feel like whatever is drawing current is drawing enough that even when runnign the battery never sees the full 14. One alternator is a little on the noisy side, but still putting out good voltage.

Battery cables still look good.

Thanks,
adam

 

[T_F_E]

It takes a good amount power to drain a 1000 amp battery in a few hours, and like you said the front battery controls the 12volt stuff. Maybe check grounds? look for shorts? I'm pretty stumped here.

 

[wallew]

rj 67,

Even if the cables LOOK good, if they are origninal, the insides could be very corroded.

But that doesn't answer the discharge issue.

Like was said, the ability to discharge one in a very short period of time means you have a SERIOUS problem somewhere.

I would ALSO check under the covers on the firewall. Look and see what they look like. You might also want to see if there is ANY corrosion on the battery terminals. That will kill a battery in a heart beat.

There are SO many possibles, that it is somewhat difficult. Hence the reason I just started replacing things and it solved most of my problems.

 

[davo727]

Assuming your trucks elec system has not been modified, my take is that your rt side alternator is dead. You say it shows 14 volts, but what you are reading is coming from the left side alt.

The way its set up the left alt puts out 14 volts and charges the front battery. It also sends 14 volts to the isolated ground of the right alt which then adds another 14 volts and outputs 28 volts to the rear battery.

So any time you start the truck the glow plug resistor bank and starter are powered 28 volts and draining the rear battery.

 

[davo727]

Do your Gen 1 and Gen 2 lights have bulbs in them? If one of them doesnt or has a burned out bulb that alternator will not charge.

And actually if the left alternator is bad it will cause the rt alternator to only put out 14 volts which makes the right one look bad when it isnt.

And do the Gen lights come on when you turn the key on and then go off at idle?

There is also a fuse in the fuse panel under the left side of dash for the right alternator that must be good or no charge.

 

[rose jackets67]

Thanks for all the replies, guys. I'll definitely take the alternators off and get them tested.

As far as the Gen1/Gen2 lights, they don't come on at all - key on/not running, at start up, or any other time. I'll check fuses and bulbs on those. I THINK fuses should be squared away, but I'll double check.

Can these alternators be tested the same as typical GM alts?


Now, even if one alternator is bad, that still doesn't cover my power drain with the truck off. I can take two freshly charged batts, both showing 12.6+ volts and put them in the truck. In a few hours, the rear battery will be low enough that the truck won't turn over... 8volts or so. That's without ever touching the key.

In my experience, a bad alt won't cause that kind of parasitic drain. I could see the possibilty of a regulator being bad or an arcing pole pulling power constantly, but I've never seen it before.

With regards to the power distribution blocks on the pass side firewall - i've had them off a few times when I was taking off old Fire Dept add ons, and all connections/terminals look sound. I haven't noticed anything alarming under the hood... at least nothing jumped out at me.

I won't have a chance to mess with the truck until middle of next week, but I'll update this thread as soon as I take a good look at it.

Keep the suggestions coming. I'm taking them all into consideration. I'll be making a real thorough check over of the truck on Wednesday, and will certainly follow all the leads posted here.

Thanks again.

adam

 

[Crash_AF]

The easy way to eliminate the alt as the problem is to charge the battery and then disconnect the alt. If the battery still goes dead, it isn't the alt itself.

The 24V side of the truck is very simple so the problem is only in one of three circuits:
The alternator
The starter
The glow plugs

Later,
Joe

 

[rotorhead]

adam, bridge across each battery when running volt meter, each should read 14. 2 or that will tell you if tour alternators are putting out, bridge across both batteries and should be appox 28.4 or so.

You mentioned you had a problem at head light.... good place to start for possable short.

Do you have a schematic for wireing? Hope this helps Jef




quote=rose jackets67;416923]First post here - I've done a LOT of searching with no luck.

A little background - I'm a LEO in Georgia, and this spring I bought a 1985 m1008 that had previously belonged to a neighboring fire dept. I drove the truck daily for about 3 months until it starting acting up.

I went to leave for work one morning, and the glow plug 'wait' light stayed on extra long. I knew what that meant before I hit the key. Yep, battery(s) dead. So i jump it and head to work.

I replaced both old mismatched batterys with 1000amp units from the local auto parts store. Same problem. Front battery stays at around 12.6 volts when the truck is off. Rear battery goes to zero in a matter of hours. As far as I can tell, there is a pretty serious drain on the rear battery, BUT, my understanding is that all 12v accessories are run off of the front battery. What could be killing the rear?

When I first got the truck, I stripped out all of the additional aftermarked items added by the fire dept as well as the wiring to them. I drove the truck for another two months without any issues, so I don't think I caused any shorts then.

Both alternators put out proper voltage at their lugs (14.1-14.3 volts), but with the truck running the rear battery never climbs above around 13 volts.

Otherwise, the truck is wonderful. Currently it has 4.10 geared axles under it and is a pleasure to drive. Generally speaking the truck stops good, runs good, hardly leaks any oil, leaks no trans fluid or gear oil and goes like hell in the mud.

The only issues aside from the power draw are the right front high beam is dead (wiring issue - known good lamp installed and it's still dead), and neither of the Gen lights have ever illuminated.

Any assistance would be greatly appreciated. I bought this truck with the intention of installing a 4 cylinder B-series Cummins, but right now I can't even move it around the shop![/quote]

 

[lavarok]

If your driver side alternator shows 14v+ at the output lug, your passenger side alternator should show 28v+ at the alternator output lug. The alts are wired in a series.

I see 4 possible scenarios:
14v at DR alt, 14v at PS alt = bad PS alt or circuit ( gen 2 bulb? )
0v at DR alt, 14v at PS alt = bad DR alt or circuit ( gen 1 bulb? )
14v at DR alt, 28v at PS alt = happy times
0v at DR alt, 0v at PS alt = both alts bad or wiring screwed ( maybe both bulbs? )

 

[lavarok]

And yes a bad ALT could kill or drain your battery.

Quote from another site:
"In some cases, an alternator may be "bad" because a rectifier diode (internal part like a check valve for electricity) no longer functions. With a bad diode, the alternator can, from time to time, actively discharge the battery when you shut the car off depending on the (effectively random) position at which it stops."

Check your passenger side alternator.

Without smoke or a burning smell, I doubt you have a 24v short in your wiring somewhere.

 

[toddclaxton]

I am having the exact same problem! What did you come up with?

 

[beaubeau]

crash is right. The alter. can draw off a Batt. if it is bad. Wireing and Exhaust I Hate!!! Good luck, Phil

 

[toddclaxton]

So I just checked and the 10vlt fuse under the dash was bad. I replaced it, now both batteries at 14.6 at the battery running!! Happy times. Does that fuze only controll one Alternator? Weird. It also seems by Gen 1 light is out. Is this important?

 

[davo727]

So I just checked and the 10vlt fuse under the dash was bad. I replaced it, now both batteries at 14.6 at the battery running!! Happy times. Does that fuze only controll one Alternator? Weird. It also seems by Gen 1 light is out. Is this important?

So your not getting the gen 1 light when you turn the key to on, not running?

Unless somebody modified the wiring a CUCV alternator should not be charging if its Gen light is burned out.

 

[rose jackets67]

Is the truck fixed? Maybe... I found a popped 10-amp fuse under the dash which I replaced, and I chased a whole bunch of wires and cleaned some connections. I didn't find anything heinous as far as corroded terminals go, but something I did worked. The volt meter is now working again, and the truck has held at 12+ volts for around three hours of sitting all connected.

Thanks for all the help. Hopefully the truck will be good to go now. I ran down the road a few miles to the service station and filled it up with diesel, and realized how much I really enjoy driving this truck.

Thanks again. If I continue to have issues with the electrical system I'll be sure to update this thread.

 

[rose jackets67]

Welp, it's not fixed. Just went out to try and start it and the rear battery was dead again. I suppose I'm going to go get both alternators tested and possibly rebuilt and then go from there.

 

[G-Force]

RJ,
Do this, disconnect the + battery terminal on the problem battery. Chsarge the battery for about an hour. Whrn you go and put to therminal back on the post if you get or hear sparks you have a current draw on that battery. Take the terminal off the post and put a test light in series with the terminal and the post on the battery. If the light lights you have a current draw on that battery. Now with the test light in series go and disconnect the + wirs on the alternator. if the light goes out the problem is a blown diode in the alternator. If it doesn't, keep disconnecting + wires until it goes out. But leave each wire off just in caes it is more than one thing. NOTE: radios with memories, digital clocks and if your door is open the dome light will also show up as a draw and light the test light. I used to work on boats and dead batteries was an every day occurrance at the marina. This was how we found the draw. From what you describe though, I would bet the alternator ihas a bad diode.
Good luck and let us know how you make out.