Electrical Help

[Matt Man]

81 k10. Should there be voltage with the key off on the two wires that plug into the alternator?

I woke up this morning to a dead battery and when I checked my battery it was really dead and took quite a while to charge back up. Once I got the battery charged back up, I started the truck and there was some smoke coming from the gauge cluster area so I shut it off. I noticed the alternator was not charging so I took it off and had it tested at the parts store and it was bad.

I got a new alternator installed and now the alternator smokes only when the truck is running and there is no more smoke coming from the gauge cluster area. I can have the key on the run position without it running and it does not smoke. I have inspected the alternator wires and they are in good shape with no issues and everything else works on the truck. I am going to pull the gauge cluster and dash out tomorrow to investigate some more.

Any ideas?

[Dead Parrot]

Of the pair, the red wire should be hot as it runs to the junction box - it is a voltage sense wire that tells the alt how much voltage to make.

The other wire, brown IIRC, will have some voltage if the key is on. It serves as an excite source to get the alt started when the engine starts. If you have an Alt idiot light, the brown wire goes to that via the circuit board. If you have a voltmeter, IIRC, it goes to a resistance wire that is about the same resistance as the Alt idiot light.

As a guess, sounds like the old alt had a diode failure. That would have let current flow with the ignition off.

[Matt Man]

Originally Posted by Dead Parrot

Of the pair, the red wire should be hot as it runs to the junction box - it is a voltage sense wire that tells the alt how much voltage to make.

The other wire, brown IIRC, will have some voltage if the key is on. It serves as an excite source to get the alt started when the engine starts. If you have an Alt idiot light, the brown wire goes to that via the circuit board. If you have a voltmeter, IIRC, it goes to a resistance wire that is about the same resistance as the Alt idiot light.

As a guess, sounds like the old alt had a diode failure. That would have let current flow with the ignition off.

Would you happen to know where the brown wire would hook up to? For some reason on my truck the wire goes to both the starter and inside the cab.

[hatzie]

Originally Posted by Matt Man

Would you happen to know where the brown wire would hook up to? For some reason on my truck the wire goes to both the starter and inside the cab.

Do you have a VOLT gauge or warning lamp?

[Matt Man]

Originally Posted by hatzie

Do you have a VOLT gauge or warning lamp?

Gauge. I am getting over 30 volts on the wire that goes to the stud off the alternator. Got my whole dash torn out right now and I am at a loss. Also, the brown wire with a white stripe gets hot inside the dash after I hook up the alternator. I thought I read that this wire goes to the ignition switch?

[demian5]

Make sure your horn isnt stuck on (and the horn is blown).

[hatzie]

30V alternator output usually means your regulator inside the alternator is out to lunch. New Chinese electrical parts aren't much better than floor sweepings.
Hopefully you kept the old alternator.

If you run the truck for long with 30v coming out of it you could fry the Ignition module, ignition coil, and any light bulbs that are turned on... not to mention the battery, radio, wiper motor, ...

The SI series alternator has three connections. The BAT stud and a plug with two regulator connections.

1. BAT is a 10 or 12ga battery charge wire that goes to a fusible link on the Junction studs on the firewall.
2. The two wire Female Packard 56 plug is attached directly to the regulator through the slot with two terminals labeled 1 & 2 on the alternator case.
   1. Terminal is the Brown ignition sense wire. In 1981 it should run to the bulkhead plug. With gauges... Inside the cab it's a Brown/White 10Ω resistance wire from the CHOKE fuse to the bulkhead plug.
   2. Terminal is the Red voltage sense wire. This runs down through a fusible link to the Starter BAT terminal. The fusible link is on the starter end of the wire is shared with the power wire that runs directly to the bulkhead plug.

The red wire on terminal 2 should be hot along with the BAT terminal.
The brown wire shouldn't have volts with the ignition off.

You can buy a regulator. You need to test the diodes to make sure they are working properly.
I'd rebuild the original if you still have it.

[Matt Man]

Originally Posted by hatzie

30V alternator output usually means your regulator inside the alternator is out to lunch. New Chinese electrical parts aren't much better than floor sweepings.
Hopefully you kept the old alternator.

If you run the truck for long with 30v coming out of it you could fry the Ignition module, ignition coil, and any light bulbs that are turned on... not to mention the battery, radio, wiper motor, ...

The SI series alternator has three connections. The BAT stud and a plug with two regulator connections.

1. BAT is a 10 or 12ga battery charge wire that goes to a fusible link on the Junction studs on the firewall.
2. The two wire Female Packard 56 plug is attached directly to the regulator through the slot with two terminals labeled 1 & 2 on the alternator case.
   1. Terminal is the Brown ignition sense wire. In 1981 it should run to the bulkhead plug. With gauges... Inside the cab it's a white 10Ω resistance wire from the CHOKE fuse to the bulkhead plug.
   2. Terminal is the Red voltage sense wire. This runs down through a fusible link to the Starter BAT terminal. The fusible link is on the starter end of the wire is shared with the power wire that runs directly to the bulkhead plug.

The red wire on terminal 2 should be hot along with the BAT terminal.
The brown wire shouldn't have volts with the ignition off.

You can buy a regulator. You need to test the diodes to make sure they are working properly.
I'd rebuild the original if you still have it.

I understand the alternator situation but this is alternator number 4 on the truck now I had the original one, the aftermarket, the one off my 67 all went bad, and now the replacement which bench tested fine at the store so I do not think it is the alternator at this point but something with the wiring. I think the issue is that my brown wire has volts all the time. Can I run a new wire to the fuse box with accessory power (key in run position) for the brown wire?

I just do not understand how it was working fine for the five years I have been driving it and now its a problem which makes me believe that something is drawing a lot of power somewhere under the dash (which explains the smoke I saw). I did check all the wiring under the dash and did not see anything damaged and is in good shape for the age. I appreciate the information which will be a huge help. I will keep investigating.

[hatzie]

Have you updated the charging system on your 1967 to the internal regulator Delco?
The alternator from the 1967 shouldn't work if it's for an external regulator. Even tho it might plug in.

DOWNLOAD the 1981 service manual from the manuals link. The wiring diagrams are in the back. Direct Adobe to page 1063 and page along from there. I believe the alternator wiring starts on PDF page 1064.

I dug into the wiring diagrams in the back of the 1981 service manual... The 10Ω bulkhead to fuse panel wire is marked Circuit 130 Brown with a White tracer for 1981.
In 1981 they appear to have it hooked via a fuse panel buss bar to the Orange Circuit 300B wire that goes back to the ignition switch.

Your ignition switch is on the top RH side of the column dead center straight down behind the cluster.

If the ignition switch isn't the culprit.

Turn the ignition on and leave the engine off.
Test all of your electrical controls one at a time.
Hopefully you'll find something that's not working.

Have you removed the instrument cluster completely and looked over the wiring behind it? And the printed circuit on the panel itself.
On the LH side you have the headlamp and wiper switch. Look them over thoroughly as well.
If you have cruise III cruise control you'll find the optical pickup and VSSB module on the back of the cluster and the cruise control module down along the steering column.



I don't trust the test benches at The Borg stores. I've gotten false bad and false good indications from them.

[Matt Man]

Well I (finally) figured it out. It turns out, I had the brown wire, and the number 1 wire hooked up backwards . The brown wire was "black" from all the years of crud built up on it. Something I did not mention was I just rerouted all the wiring for the engine and placed it in conduit. I replaced all the connectors such as the alternator, distributor power wire, etc. So I must have wired it backwards even though I did it one at a time. So my wiring "improvements" ended up eating 3 alternators and a few days of my time but this is what happens when owning a old truck. At least I understand GM alternator wiring better and got to look at all my under dash wiring up close and surprisingly is in very good shape. Thanks for the help from everyone that replied!

[SunSoaked]

[hatzie]

You can probably fix the dead units fairly cheap and easy.
Test the diode trio and the diodes in the rectifier pak. Replace the bad bits. The trio is around $12 the rectifier is around $15.
Replace the regulator. It's around $15-$20
Replace the brushes on the old alternator... obviously the new ones have new brushes.

[Matt Man]

Originally Posted by hatzie

You can probably fix the dead units fairly cheap and easy.
Test the diode trio and the diodes in the rectifier pak. Replace the bad bits. The trio is around $12 the rectifier is around $15.
Replace the regulator. It's around $15-$20
Replace the brushes on the old alternator... obviously the new ones have new brushes.

I kept one of the "old" alternators to try this out with. Thanks again!

[Pontiac1976]

Well I hear your pain.
But good job in finding it.
As said by hatzie SI,CS144 ALT 8-10 min tear down repair in most cases ( the most problems is the 4 out side case small screws seizing and breaking. Or they over worked over heated to long then more parts are needed.
All ways good to have one extra for parts or spare.