Generator test

[Tongloong]

I read all 15 pages of the Charging system sticky and I still have a question. My front battery is not charging. The alternators were bench tested good two weeks ago and the batteries are tested good. I replaced the Gen 2 light, Voltmeter relay, Gen 2 relay, and now the positive bus bar is reading 24v when disconnected from the battery. Still, my front battery is dying. Also, when I do the ignition off brown wire test I found in the sticky, I am getting 12v on the Gen2 brown wire with the ignition off. I believe the only thing I have not replaced on the Gen2 circuit is the diode. With the engine at idle, and the battery disconnected, the positive bus is getting 26v, not 29. I would appreciate any help.

 

[cpf240]

The front battery is charged by the left-side alternator, GEN1....

 

[Tongloong]

I keep reading that but i don't see how. Also to add to the above post, the 28v, heater, and ignition fuses are good.

 

[rlltide12]

I dealt with this issue the other day. Could be your problem. Local FD brought me their m1028 that wasnt charging. Turned out to be a ground wire was missing on the ground pin on the drivers side alternator. Take a jumper wire and make sure that the post on the back of the alternator on the drivers side has a ground. It should go to charging when you ground it.

 

[Tongloong]

Thanks, I'll play with that in the morning. I just started the truck after being on the charger. There are some things that are weird to me. 1. When I disconnect the no.1 battery ground to the frame, and bridge my multimeter between the frame of the truck and the negative terminal of the no.1 battery, I get 12v. I thought this was a stray voltage test (for 12v systems), I got 13v between the frame of the truck and the positive post of the no.1 battery. Do I have a 12v short that doesn't blow fuses and still allows everything to run? 2. The no. 1 alternator when at idle measures 12v at the thick battery lead. When I disconnected the battery wire and took another reading, it bounced between 16.5-17.4v. Is this correct? shouldn't it put out 14v+? 3. when I do the test in the sticky, the brown wire on the no.2 generator has 12v with everything off. Is this normal? Or, does this support some kind of 12v short as mentioned before?

 

[rlltide12]

When you say #1, do you mean front or rear?

 

[rlltide12]

Battery that is

 

[Tongloong]

front battery

 

[rlltide12]

Then if you disconnected the ground and the truck continued to run, then the drivers side alternator is charging. Otherwise you would have lost your 12 volt feed to the injection pump fuel shutoff. Does all 12 volt components such as headlights work?

 

[Tongloong]

Yes barely. When i turned everything on to load test the alternators the voltage dropped to 22 ish.

 

[rlltide12]

Have you measured the voltage across the two posts on the drivers side alternator in normally hooked up conditions?

 

[Tongloong]

not across the alternator posts, only from the battery post to an engine ground. I'll check it tomorrow and see what we find

 

[Tongloong]

Ok guys, First, thanks for your help this far and sorry for the delay. My day job still gets in the way of play with the truck time. I checked the ground on alt 1, the cable seems solid, did a resistance test with the ohmmeter and it looked good. I ran a jumper wire from the ground post to the alternator bracket and got no change. I checked the voltage across the two posts on alt 1 and got 12.4 which is the current voltage for battery #1.
Here's where it gets weird. When I disconnected the battery wire (large red one) and tested the output voltage (alt1) between the two posts, pos/neg, It was bouncing between 19-20vdc. Since it had an output, though too high, I took it to autozone. They tested it and said it is good. So, now I'm really confused. I did check the voltage across pos/neg on battery no 2 and got 14+v so at least alt 2 seems to be working. I'm thinking about swapping alternators tomorrow to see if the charge moves to the front battery. They are both stock isolated ground.

 

[rlltide12]

Quite the challenge. Something must be wrong with the voltage sense wiring. I believe its possible the module in the alternator is bad. Try this. Crank the truck, then unplug the two pronged plug on the alt. May not make a difference. But it could.

 

[rlltide12]

http://bob_skelly.home.comcast.net/~bob_skelly/alternator_conversion/wiring_alternator1.html good read. Not quite the same alternator but same concept

 

[Tongloong]

Just to update you guys, I took the alternator in question to a real alternator/starter shop and they replace the voltage regulator. This presents another problem. You said up front to look at the ground and I think I may be back to that. I removed the ground wires and from pole to pole I get 15v. When I add the little black wire (no idea what it is) I still get 15v but no charge to the battery. When I add the thicker ground wire, it's back to 12v of output. I will replace the ground wire tomorrow just to be sure that is not part of the problem. I'm about to the point to start pulling one wire at a time in a search for any hidden fusible links or shorts. Given the state of overall age and dryrot, do you guys know where an engine harness can be purchased? I noticed that the TM talks about removing the front harness. It might be worth it at this point to alleviate any other problems with this wiring.

 

[cpf240]

If we are talking about GEN1, the drivers-side alternator, then the little black wire is probably the tach output for the diagnostic connector under the dash.

As for a wiring harness, unless someone has some NOS ones out of surplus, the only ones available will be take-outs from other trucks, and likely just as old as yours, though they may be in better condition.

 

[number9er]

Given the state of overall age and dryrot, do you guys know where an engine harness can be purchased?

I started a thread about replacing the charging/starting circuit cabling. There are so many different ways to do it that I've decided to just replace the damaged cables with the spec gauge until I decide exactly what I want to do. There could be a case made for documenting building a new harness to spec (or upping the gauge by 1 on the higher current circuits - but once you start modifying the spec, it's hard to stop). At any rate, building a new harness wouldn't be too hard and would likely be an improvement on even NOS parts.

 

[rlltide12]

Id take the large black wire off and use a jumper cable or jumper wire and jump from the negative pole to the negative post on the battery. That wire could have a short in it.

Edit: short....idk what im thinking. Grounds dont short. But you could have a bad ground. Thats what i meant.

 

[number9er]

A bad connection - yes. A short - unlikely. That's one of the few wires on that truck that should be able to touch ground. It's path to the negative terminal is from the neg terminal on alt 1 to a point (close by) on the engine. Then from a point on the back of the engine to the negative bus on the firewall, and from there to the negative post on the front battery.

This may be a silly question but have you had the batteries load tested?