Running on Batteries....

[combatmech]

Howdy all,
I am stumped.....
New batteris, reworked alternators. It starts and runs like a champ. after about 20 min, the lights go dim, seatbelt light comes on....turn the truck off, try it again and no start. Not getting any indication that the Gen's arent doing their job ( cept just running on batteries ) no other lights come on to warn me of any failure. My voltmeter has never worked.....So I really cant tell.

I have cleaned all the grounds, except for the bus bar.....There are two wires going to studs near the glow plug relay that are pretty rusty....not sure what they do.....

What excatly is a "fusible link"? What does it look like? How would you check to see if you have a bad one?

Any other suggestions gents???

 

[notsosanestan]

do your gen 1 and 2 lights come on when u turn the key?

 

[combatmech]

Yes..seems to be the only time that they do. The Gen2 relay when plugged in, light stays off, when pulled, light stays off. Same with Gen1 relay.
Prior to all this Gen2 relay was out and no light, installed, light came on with engine running. Faint Gen1 light when running heater fan with lights on.

 

[notsosanestan]

mine only comes on for a sec when i start it up then give it a rev it goes away. if the light comes on with the fan being on i think that would have to be the alternator or the belts are slipping you cant hear them over the engine noise.

 

[ida34]

There is something else going on besides alternator problems. It the batteries had enough charge to start the thing I do not see how you could be going down after only 20 minutes. First off, all the lights will run off the front battery only. The rear battery will only show problems on start up as it only is used for the starter and glow plug system. The only other thing the rear battery runs all the time is the volt meter and military radios if you have them installed. You can now focus on the front battery and the driver's side alternator. Having said that it sounds like something else is going on except a simple charging problem. Do you have to charge the front battery again before it will start? The two studs you speak of on the firewall over the glow plug relays sounds like the 12 volt terminal strip. It is just a common junction point for 12 volt stuff. Sounds like you have a bad connection somewhere. The extra resistance of a bad ground or bad connection can draw down lights and make them dim. The seat belt light coming on concerns me. I would first track down why this light is coming on by tracing that circuit. The wiring diagrams are in the -20 in the manuals section. TM-9-2320-289-20.

One other thing. What you think is the gen 1 relay is not. There is no relay for the driver's side or number 1 alternator. There should be three relays total where the gen 2 relay is. The other two work the starter and the voltmeter.

 

[ida34]

I almost forgot. The first place I would check is the engine wiring harness block as it is called in the schematic. It is the terminal posts above the glow plug relay. A bad connection there will cause your problems. Bad connections also create heat with the resistance so if the wire is unusually hot there is a good chance of a bad connection. Also, wires corrode internally sometimes and you can't see it. This will cause a bad connection inside the wire. This mostly happens near the acid of the battery but can happen anywhere.

Also, when this problem occurs use a multimeter to check the voltage at both batteries individually. If they have 12.5 or so volts then both of them are charged. This is when the truck is off. It should be closer to 14 volts when the truck is running. No matter how charged the batteries are if the starter does not get the impulse to engage the solenoid then it will not start. Also when this happens check the voltage on both sides of the engine wiring harness block.

 

[combatmech]

Looking at the wiring figures, and looking abck at when the alternators were removed, I had an extra wire coing from the ground post on the #2 gen. It looked like a small ground wire.....I have no idea where the other end is. Looking at Fig10, it shows that both gen's ground wires go to the engine ground. Is it the ground near the #1 gen, or is it the ground on the back right side of the engine?? Could this also be a voltage regulator problem??

 

[gaunt1969]

gen-2's ground is isolated from the eng or frame ground . it does not go to ground. only gen-1 ground goes to eng or frame

 

[combatmech]

Hey Chuck,
Think you hit the nail on the head. I was doin more T/S and found a red/blue wire, from #2 Batt negative side to engine wiring harness block that gets really hot while the truck is running. I tried to clean up the studs on the block, still acting funny. This block isnt something I can pick up at autozone??