1980 Diesel Pickup eating batteries

[supersisu]

So the alternator light came on a few days ago. I bought a new alternator, put it in, light goes off. Drive for a day, next morning dead (pretty new) battery. I figured that a dead voltage regulator on the bad alternator fried the battery, so I put in spare (very new) battery. Drive for a day, next morning dead battery. When I hook them up to a (cheap) charger, the needle goes down to zero and the green "fully charged" light is on. I'm stumped and it's cold and I'm riding a bicycle in Chicago. Thoughts would be very appreciated.

[TylerDurden]

My caddy would kill my battery until I found the GP relay was sticking on.

Got a water leak? That's what screwed up my GP relay.

[82vdub]

First, is the battery dead, or is the starter dead?

If the battery accepts no amp draw, then it's either stone dead, or it's charged. What's the voltage on the battery? It should be 12.4V+ for it to be charged with decent power to start the vehicle.

If the battery has good voltage but the car won't start, turn on the lights. If they are nice and bright, the battery is confirmed to be pretty good.

Check battery connections and connections on the starter to make sure they are snug. Lots of times a large amp draw will cause a not so good connection (high resistance) to not pass power, and things don't work like they normally do.

If the battery is truely going dead overnight, then you've got an amp draw somewhere. As mentioned before, start pulling relays until the amp draw goes away. The relay guts rust when they get water in them from a leaking windsheild and then sometimes short out, causing a pretty good draw on the battery. If it's not a relay, then start figuring out which fuse is the one that has the amp draw to narrow down the search to where else you may need to look for the culpret.

[Fatmobile]

A voltmeter comes in pretty handy for troubles like this.
Knowing what the battery voltage is when it's "dead" would help.
Putting the battery cable on in the dark and watching for spark can help see when there is draw. Even a radio or clock will make it spark so if you don't have a voltmeter you can pull a fuse/relay and look for spark.

Sounds like it's already charged when you go to charge it
so crank for awhile and feel for hot spots on the cable connections.

[supersisu]

I've got about 12.5 v on both batteries. I put them on another charger today (I forgot the charger that read "full charge" has something wrong with it and doesn't really work, now it's in the garbage so I don't get confused again) and they both pulled about 5 amps (25 percent charge on the scale) at first. Just checked after about 4 hours and the charger shows 0 amps, but the charger is super warm and I'm thinking it fried out?

Thanks for the advice so far, a couple other points I forgot to mention: I took the batteries out at night and brought them inside to keep them warm. Then reinstalled, waited for glow plug light to go out, engine moved briefly (not cranking, probably not even half a turn). Horn did not work (my check for dead battery). A jump didn't work on my first battery either. Terminals were pretty tight (I have had them jump loose from starting amps in the past).

I've had starters go before (not vw but others) and they either slipped from worn teeth or didn't do anything until I hit them with a hammer or rocked the car back and forth. I do have a good spare....

If it's halfway decent tomorrow I'll try my possibly charged battery. Or I'll just ride my bicycle, it's only 4 miles and it's actually pretty beautiful out.

[colby]

You should be able to find a draw by this (I have never tested this, but was advised by a friend who is an ASE Master Mechanic). Disconnect the negative battery cable. Insert a test light between the negative cable and negative post (alligator clip on cable, test light probe on negative terminal) If it lights up, there is a draw. If there is a draw, start pulling fuses until the light goes out, and then you have your culprit.

The earlier Volkswagens are notorious for a bad ground connection, so I would look there as well. You need a very clean grounding connection. Use vaseline to protect it from corrosion. I think the A1s mounted the ground on the transmission mount. Up here in the northeast, they use salt and calcium chloride on the roads and it makes for a nasty electrical mess if it finds its way to a connection.

Colby

[82vdub]

Welcome back colby (or to ) to the forum.

Yes, you can insert a test light in line as colby mentioned. However, any radio that has a clock or otherwise hot connection to it will show a draw here. However, the light, I believe, will be dimmer with less load on it.

It sounds as though your not getting power out from the battery to the chassis, or to the starter. Have you measured the battery voltage at the starter and measure it when someone turns the key? Check for 12V on the solenoid wire (that's energized by the key) too. A remote starter is great for troubleshooting if you have a starter problem or a chassis wiring problem. There's a big fat wire going from the battery to the starter. If this has good connections and is solidly connected to the wire, using a remote starter should turn the engine over. Make sure it's in neutral first.

[Fatmobile]

12.5 volts isn't real good.
I wonder what it was after you charged it.
Feel for any hot connections?

[supersisu]

Got battery #1 (the older one) charged up pretty well. Reading about 12.5 volts. I put in the truck this morning, horn worked. Glow plug light went off, BUT I didn't hear or feel the GP relay click off as usual. Truck started fine, alternator light off. I've pulled the GP relay and will let the truck sit overnight with the battery installed and see what happens tomorrow. GP relay looked okay, no obvious corrosion.

Thanks everybody.

[colby]

The glow plug relay does not shut off after the light goes out. It normally shuts off after the engine starts. The light is just an indicator to tell you, "OK, you can start me now". You should hear it click off after the engine is running. Best way to determine if its sticking on is to wire up a 12v LED to the glow plug fuse so you know when its actually getting power.

Colby

[supersisu]

The latest: Started truck this morning with fully charged battery (reading 12.5 v). Voltage across battery terminal while truck is running: 12.5 v. Revving engine didn't change voltage at all. I'm assuming that the alternator is contributing nothing and that the truck is running off the battery?

Alternator light not on, I'm planning on spending some time Saturday morning checking grounds etc.

I drove around last Friday, truck worked fine until I had to turn on the lights. Then battery rapidly depleted, dim lights, slow flashers. It kept running though.

[colby]

When you turn the key on, does the battery light come on until you start the engine? I believe this light is responsible for exciting the fields in the alternator, and is controlled by a single wire.

Colby

[82vdub]

You are correct that if the vehicle has 12.5v before starting it and after, then the alternator isn't charging the battery.

Since I've recently had an issue with my winter Jetta for the same thing (1.8 gas), I found that my idiot light for the battery was not working 100% of the time - meaning that there's a short somewhere in the small wire going to the small terminal on the alternator. I've rigged up a voltmeter to tell me when it's charging and when it's not, but, other than finding and fixing the issue, there's a couple things that can be done.

You can rev the engine to 3000-4000 RPM and the alternator should self-energize the doide field (or whatever it does) and start charging.

Change the voltage regulator on the back of the alternator to a one-wire style, where it doesn't need the small wire coming from the idiot light.

You can rig up a 12V wire with a resistor in it that's energized when the key is on and goes to the small wire on the back of the alternator. The resistor has to be the same as the resistance of the idiot light circuit.

None of these solutions makes the idiot light in the cab work to inform you when your alternator isn't charging. So, besides finding out why the small wire (if this is the actual problem) doesn't energize the alternator at around 1500RPM, these are alternate ideas. I talked to my local rebuilder on the one-wire voltage regulator (like GM's use now), and he looked it up and they do have them available for my Bosch style alternator that was for my gas Jetta. Ole 82 has a different style alternator, and I do not know if the one-wire style voltage regulator was available for that style or not.

I've run Ole 82 all the way from outside St. Louis, MO to Green Bay on just the battery before. With a fully charged battery and the old style injection pump (mechanical), they will run a long time as the only thing that was operating was the fuel shutoff solenoid, and any brake lights. It was during the day, no AC, no radio, no nothing that wasn't required. Too bad my fuel pump in the gas Jetta starts to quit after going 2 miles when the alternator isn't working.

[supersisu]

Just checked, battery light does not come on with ignition.

Here's a question: There is a rubber plug with three wires (two red and one blue, I believe) that plugs into the back of the alternator. There is also a male spade connection on the back of the alternator that had nothing connected to it when I removed the bad one. I looked for a loose wire, didn't see anything hanging, so I figured it was extra. Did I miss a ground somewhere? The red book also mentions (but does not show) a ground strap to the mounting bolt? The wiring diagram shows something too. I'm going to check in the morning more carefully.

[colby]

The single red wire in the back of the alternator separate from the 3 wire plug is probably the RPM signal for the oil pressure sensor. Its been a while since I looked at one of those alternators but the signal wire for the alternator that energizes the field is usually a small gauge wire. My guess is you don't have 12v on that wire, or the wire could be damaged upstream causing the signal not to flow when the key is "On".

Colby