1031 Rear Battery Not Charging

[Broadsword]

For some reason the rear battery on my 1031 doesn't seem to be receiving a charge. When the truck is running, both alternators are producing 14.5 volts and the front battery is receiving 14.5 volts, however the rear battery only reads 12.5 volts. Both batteries are brand new, and I have no GEN lights showing.

What should I check?

Thanks

*EDIT* - I checked the GEN lights and the GEN-2 bulb was missing . I replaced it and now it stays lit.

 

[Keith_J]

Positive wire from the right alternator to the rear battery positive terminal. My guess? Fusible link has been scorched.

 

[Broadsword]

Positive wire from the right alternator to the rear battery positive terminal. My guess? Fusible link has been scorched.

Before I tear apart the loom, do you happen to know where that fusible link is located?

 

[Keith_J]

Fusible links are not supposed to be under tape, loom or conduit. In your case, it is right under the second lug on the main 24 volt positive buss. Second lug from the right, it is a blue silicone wire.

See Appendix F, frame 9 of the -20 TM. Also sticky at the top of this page. Good luck finding a 12 AWG fusible link, I suggest NAPA but not all NAPAs are the same.

 

[Skinny]

Blown fusible links make me nervous, sounds like you may have a compound problem.

Anyone have a writeup on replacing the fusible links with a automotive maxi fuse or something like that? Fusible links went out with the 80's

 

[Keith_J]

Use a fuse 150% of the designed current in the circuit as the base, if current isn't known, then go on wire size. 12 AWG should be protected by a 20 amp fuse, 14 AWG would be 15 amp, 16 AWG 10 amp...

For alternator output, a 150 amp fuse would be adequate.

 

[Broadsword]

Fusible links are not supposed to be under tape, loom or conduit. In your case, it is right under the second lug on the main 24 volt positive buss. Second lug from the right, it is a blue silicone wire.

See Appendix F, frame 9 of the -20 TM. Also sticky at the top of this page. Good luck finding a 12 AWG fusible link, I suggest NAPA but not all NAPAs are the same.

I found the fusible link. Looks fine and tested out fine. I also pulled the loom apart and verified its integrity from the 24v positive bus all the way to the passenger alternator.

Whats next?

 

[MarcusOReallyus]

Hmmmm....

How are you measuring the voltage at the alternator? How about the batteries?

Where are you getting ground for each measurement?

 

[Broadsword]

What about the diode? I found it wrapped in duct tape (not a good sign) and I have no power passing through it.

 

[Keith_J]

Are you measuring the fat, 8 AWG wire on the back of the alternator? I guess it is possible for a break in the wire other than the fusible link.

 

[Broadsword]

With the truck off, I have the following readings on the back of GEN 2. Readings were taken with a voltmeter using the body ground from BATT 1 (Front).

#2 (25v)
#1 (12.9v)
+ (25v)
- (12.5v)

 

[Keith_J]

It could be the diode. You realize it only conducts current in one direction so with your ohmmeter in the 200 scale, test it in both directions. Red lead on anode and black on cathode should conduct, black on anode and red on cathode will not.

You can find replacement diodes at Radio Shack, see the CUCV wiki/FAQ. You will have to use the existing connector, either soldering or crimping.

 

[Broadsword]

Yeah, I was testing the diode in the wrong direction. It seems to be working fine.

I also checked the GEN 2 Relay, and it seems to be working fine too.

I started the truck again to see if I accidentally fixed something. Still only getting 12.5v on the rear battery, while getting 14.5 at the front. I noticed that the GEN 2 light would flicker and dim when I revved the engine, so I tried tightening the belt, but that didn't change anything either.

The alternator appears to be working right, all the wiring is intact, diode is good, relay is good, but the rear battery still isn't receiving a charge? What am I missing?

 

[Keith_J]

As an EXPERIMENT, connect a length of 12 AWG from the right alternator directly to the rear battery positive to see if the alternator is producing current. This will show if the main lead from the alternator to the battery is good.

 

[Broadsword]

Test didn't work.

I'm starting to think that my GEN 2 is not working after all. Originally I tested the output and got 14.5v, but I was using the body as a ground. When I tested using the negative terminal on the rear Battery as a ground, I only got 12.4v (same as the rear Batt).

So where should I get a new Alternator?

 

[Warthog]

If the bulb is lite then your alternator needs a rebuild.

As you found out, start simple. The bulbs are required to be working for either alternator to work.

Fusible links are still used today. Unless you are an engineer and understand automotive electrical systems, replacing fusible links with something else is not a good idea.

Let's say you replace the link with a maxi-fuse, what size would you use? Is it too big and will the vehicle wiring burn up first before the maxi-fuse blows? Without fully understanding the requirements may put your vehicle in danger. Of course YMMV.

 

[Keith_J]

Test didn't work.

I'm starting to think that my GEN 2 is not working after all. Originally I tested the output and got 14.5v, but I was using the body as a ground. When I tested using the negative terminal on the rear Battery as a ground, I only got 12.4v (same as the rear Batt).

So where should I get a new Alternator?

You need to do further testing. Print out Appendix F9 and trace all the wires. There are TWO fusible links going to the alternator, the large one you have already tested, the smaller one is what the alternator's regulator uses to sense charge state. This is an orange fusible link, under the same #2 terminal the larger blue fusible link is attached to. This is why you can have voltage higher than 14.5 at the alternator terminal yet have 14.5 at the battery, voltage drop over the fat charge wire.

Pull the plug out of the alternator (it has a retention clip, don't break it) and measure the voltage of the #2 connector on the plug, it should be 24+ volts to chassis. If not, that fusible link is broken.

If the idiot light is good along with the voltage regulator, a break here will NOT illuminate the idiot light.

If you have exhaustively tested all the wiring and find the problem IS the alternator, it is far better to rebuild it yourself. CUCV Electric has all you need and a good write-up on how to do it.

 

[cliffyp]

If you have exhaustively tested all the wiring and find the problem IS the alternator, it is far better to rebuild it yourself. CUCV Electric has all you need and a good write-up on how to do it.

As a total novice I rebuilt my alternator with their kit and followed the TM. Wasn't difficult, didn't take long and fixed my charging problem.

 

[Broadsword]

***UPDATE***

Thanks everyone for the advice on CUCV Electric. I ordered up the full rebuild kit and followed the online instructions. The kit shipped out quickly and the instructions were easy to follow.

I finished rebuilding the alternator last night, and re-installed it in the truck this afternoon. It seems to have solved my charging issues... sort of. At idle I'm only getting 13.3v. At a fast idle I get 14.1v. The GEN2 dash light is dimly lit at idle, and goes out completely if I rev the engine.

I'm happy that its at least somewhat charging, but something still seems to be off.

 

[doghead]

Your idle is probably a bit low.