86 CUCV Blazer(still 24v); Batteries completely discharged

[Kantrol]

Been having some electrical issues with this truck. I started with the simplest thing and got the older of the batteries tested, it was bad, so I bought a new redtop and put it in. Fired up on the first crank yesterday, let it idle for 15mins, and everything seemed good. The alternator lights didn't come on when it was running.

Get in it today to check to see if the problem had been corrected and the electrics are completely dead. No lights illuminate(i.e. glowplug, alt, oil) and the battery/volts gauge reads at the bottom of the read. Which tells me(I assume) one of two things:
1) The other battery(a redtop from 09) isn't holding a charge either and discharged both batteries
2) I have some sort of parasitic electrical drain on the vehicle. There is an aftermarket radio installed but I'm not sure if this could be the problem since the PO didn't seem to have a problem with it. I don't think this is the case since it's wired into the service lights I think.

Any other ideas?

 

[Warthog]

Always start troubleshooting an eletrical issue with the batteries fully charged and load tested.

Have the GEN1 and GEN2 lights been coming on at all? What about when you first turn the key on?

The bulbs/lights are part of the charging circuit. If they are not working then the alternators will not charge the batteries.

 

[DokWatson]

You have to replace both batteries at the same time.

And this doesn't even sound right at all and should be looked into, "There is an aftermarket radio installed but I'm not sure if this could be the problem since the PO didn't seem to have a problem with it. I don't think this is the case since it's wired into the service lights I think."

I can think of a lot of better places to get power for the radio, what else could they have done in there?

 

[NMC_EXP]

Have the GEN1 and GEN2 lights been coming on at all? What about when you first turn the key on?

The bulbs/lights are part of the charging circuit. If they are not working then the alternators will not charge the batteries.

Burned out ALT idiot light bulbs will break the alternator to battery circut?

Thanks

Jim

 

[davidkroberts]

a bad battery will fry an altenator, you adding the new battery might have just masked the problem by providing more power in a dead system. I would test the altenators. Was it the front battery or the rear battery you replaced. If it was the front one it charges from the drivers side altenator, check that one first. Its the easiest to source a replacement anyway.
If its bad and you get another one at the parts store that test it make sure you dont turn in the core for the charge. Its more valuable rebuilt as an isolated ground replacement incase your passenger side fails. Get it rebuilt and keep as a spare

 

[Warthog]

Burned out ALT idiot light bulbs will break the alternator to battery circut?

Thanks

Jim

Yes. On the CUCVs the idiot bulb is part of the alternator excitor circuits. Bulb not working then no excitement to the alternor and no charging.

 

[NMC_EXP]

Yes. On the CUCVs the idiot bulb is part of the alternator excitor circuits. Bulb not working then no excitement to the alternor and no charging.

I wonder what the GM engineers were thinking when they came up with the idea of a couple of delicate 25 cent light bulbs being the difference between an operational or a dead $29,900 vehicle.

At Caterpillar a currently popular management buzz phrase is "robust design". Best I can tell it means idiot proof and gremlin proof.

This design does not qualify.

Regards

Jim

 

[Kantrol]

To answer a couple of questions:
Dashlights: All the idiot lights on the dashboard light up when the system is charged and the key is in but the engine is not running. The last time I started it all of the idiot lights went out once the vehicle was started. The battery volts gauge reads below the tick mark in the green but still in the green.

Either the battery/volts gauge is broken or reading low(wouldn't surprise me based on previous experience with the gauge in other vehicles) or one of the alternators is not putting out proper voltage. In either case, it doesn't explain how the system drained two batteries overnight, right?

Radio: Maybe I failed to understand the circuitry of the vehicle. The radio will only turn on when the service light switch is set to on.

Alts: The PO switched out the GEN2 alt prior to my purchase.

Battery: I replaced the front battery.

So...my first trouble shooting step should be pull the alts and get them load tested.

 

[Warthog]

So...my first trouble shooting step should be pull the alts and get them load tested.

No.... your first step should be to have the batteries charged and load tested. Maybe your "new" battery was bad from the factory or the second battery also has a bad cell. You woun't know until you test them

The second step is to test the alternators. If you have a voltmeter you can do it yourself or take them out and have them tested.

A bad alternator can drain a battery in nothing flat.

NEVER trust what a previous owner did until you verify it yourself.

I would disconnect the radio until you figure out the truck issues. No need to have another unknown to deal with.

 

[Kantrol]

Fair enough. I charged the batteries last night. Took them off the charger and put them in the truck and fired it up. BVG still reading below the tick mark. Should I leave them in the truck and see if the problem repeats itself(I'm pretty sure this is no because discharging car batteries is bad for their longevity) or just pull them now and get them tested?

Edit: Got the batteries tested; both are good. Disconnected the radio. So...my game plan should be pull the driver side alt and see if it's bad or reinstall the batteries and see if the problem repeats itself?

 

[Barrman]

Now that you have a pair of known good batteries. Test the alternators with the engine running. 14.4 volts each and 28.8 total across both batteries. If you have that, then they are both working correctly. They might not be shutting off correctly though.

Are either of the GEN lights dimly lit with the truck off? Since those lights are part of the "exciter" wire circuit, they are the only way power can be going from the batteries through the alternators to ground and run things down. Besides the cases grounding out that is. If you have that though, you should be getting a big spark installing or removing any battery cable.

Do you get a spark pulling a battery cable? Is it welding arc strong or just a trace of one? Either way, front battery means drivers side and back battery is passenger side. If you are getting a spark, unplug all 4 battery cables. Plug in just the rear battery cables and look for the spark. Un plug the rear and do the same with the front. It will probably happen on the front battery since the entire truck runs off that one except the starting/glow plug and slave systems. Your mention of a radio makes me think something else was messed with on the truck and is now broken.

If you get a spark, unplug the plastic plug on the alternator that goes to the battery you were testing. Now, do the terminal test again. Spark gone means you have an internal problem in the alternator. Spark still there means you get to start pulling fuses and doing the battery terminal test over and over again until you figure out which circuit has the short.

Download and look through the -20 manual for the truck. It talks you through everything I just wrote in different words, but same basic result. The -20 really has to be your guide when working on these trucks.

 

[Kantrol]

Got the drivers side alternator tested; bad voltage regulator. That should explain why the the front battery dies overnight, right?

What's the recommended replacement?

 

[Warthog]

You can have it rebuilt for ~$100 or you can rebuild it yourself.

You can replace just the regulator or rebuild the whole thing. Easy to do and the TM 9-2320-289-34 covers it in detail.

High Output Alternators - Alternator & Starter Repair Kits - Alternator Parts - HEAVY DUTY REPAIR KIT

or

http://www.springhillautoelectric.com/index.php?act=viewProd&productId=1650


If you have it apart I would replace all the internals.

 

[Kantrol]

I got the kit in and rebuilt the alternator today. Put the alternator back in, got it adjusted so the belts don't squeal under throttle. But I'm still having problems...
1) The Gen lights turn on when I turn the key to run and go off when I start but the volts gauge doesn't make it into the green portion of the voltmeter gauge. The fuses are good and the voltmeter was good before the drivers side alternator went out. The fuses specified in the -20 manual are both good.

I will freely admit that I likely screwed up the rebuild but the pictures of the completed alternator internals that I found on SS matched up to what I had and I followed the instructions in the -34 manual. Should I buy a new alternator and have my current one professionally rebuilt? It's the drivers side alt so it doesn't have be isolated ground, right?

2) Unrelated, but I turned the wipers on for some reason and now they don't go off. Is there a fuse I can pull or do I have to open up my steering column to get them to turn off. Search wasn't very helpful for figuring this out...

 

[Kantrol]

Drivers side alternator confirmed good at autozone. Started the truck, reading 12.20v across the front battery posts and 14.7 across the rear battery posts. Which means there is some sort of drain on the front battery?

The glowplug circuit runs off the front battery, correct? I'm leaning towards some sort of failure in this circuit. The truck blows white smoke on startup(indicates bad glow plugs?). Glow plug relays go bad frequently, right? I get a mild spark when connecting the negative battery terminal on the front. It's not trying to weld the cables to the post but it's noticeable.

So...my next step is: figure out if the relay is constantly energized by...? While I'm doing that I figure I might as well figure out which plugs are bad and replace them since it's blowing white smoke on startup.

 

[Barrman]

Pull the power supply to the glow plug relay and see if the spark is still there when you hook/unhook the battery. If the spark is gone, then you found the area of the problem.

A stock truck uses 24V to power the glow plugs. That huge block held on by 3 bolts behind the engine on the firewall is a resistor that steps the 24V down to 12V which is what is supposed to actually go to the glow plugs.

Do you still have the big resistor?

 

[Kantrol]

Still 24v truck.
-Connected the batteries, started the truck, reading 11.6v across the front battery. Which is normal since the GPs should stay on for like a minute after starting, right?
-Turned the truck off(key in off position), still reading 11.6v across the front battery.
-Disconnected the wire from the top post of the GPR, reading 12.2v across front battery.
-Disconnected the battery, reconnected the wire to the GPR, reconnected the battery and the terminal arced against the battery cable.

All signs point to a GPR that remains energized after the key is out of the run position. Is there any other reason why the GPR would still be getting electricity after the key is out of the ignition?

 

[Barrman]

I wasn't trying to argue. The charging and starting system can still be 24 Volts while just the glow plug system has been switched over to 12V. Since your front battery seems to be taking all of the glow plug load, I thought maybe your glow plug resistor had been bypassed and the wiring changed.

Yes, I agree that your relay is sticking.