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Old 03-28-2020, 11:37 PM   #1
Matt Man
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Electrical Help

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?
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86 c30 crew cab dually 454/400 4/6 drop SOLD 1-8-11
1981 chevy K10 shorty 350/350C 12bolt, 10bolt, NP208
4" lift 35's
4.10's Detroit locker/Truetrac
Vintage Air
67 GMC Stepside Straight six/3 on the tree "The Peach"

K10 build http://67-72chevytrucks.com/vboard/s...d.php?t=671934

The Peach build http://67-72chevytrucks.com/vboard/s...d.php?t=733903




Last edited by Matt Man; 03-28-2020 at 11:51 PM.
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Old 03-29-2020, 11:40 AM   #2
Dead Parrot
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Re: Electrical Help

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.
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Old 03-29-2020, 11:17 PM   #3
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Re: Electrical Help

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Originally Posted by Dead Parrot View Post
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.
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86 c30 crew cab dually 454/400 4/6 drop SOLD 1-8-11
1981 chevy K10 shorty 350/350C 12bolt, 10bolt, NP208
4" lift 35's
4.10's Detroit locker/Truetrac
Vintage Air
67 GMC Stepside Straight six/3 on the tree "The Peach"

K10 build http://67-72chevytrucks.com/vboard/s...d.php?t=671934

The Peach build http://67-72chevytrucks.com/vboard/s...d.php?t=733903



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Old 03-31-2020, 06:06 PM   #4
demian5
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Re: Electrical Help

Make sure your horn isnt stuck on (and the horn is blown).
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Old 03-31-2020, 08:49 PM   #5
hatzie
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Re: Electrical Help

Quote:
Originally Posted by Matt Man View Post
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?
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1967 Dodge W200 B383, NP420/NP201 SOLD
1969 Dodge Polara 500 B383, A833 SOLD
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1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
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Old 04-01-2020, 11:25 AM   #6
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Re: Electrical Help

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Originally Posted by hatzie View Post
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?
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86 c30 crew cab dually 454/400 4/6 drop SOLD 1-8-11
1981 chevy K10 shorty 350/350C 12bolt, 10bolt, NP208
4" lift 35's
4.10's Detroit locker/Truetrac
Vintage Air
67 GMC Stepside Straight six/3 on the tree "The Peach"

K10 build http://67-72chevytrucks.com/vboard/s...d.php?t=671934

The Peach build http://67-72chevytrucks.com/vboard/s...d.php?t=733903



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Old 04-01-2020, 12:48 PM   #7
hatzie
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Re: Electrical Help

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.
__________________
1959 M35A2 LDT465-1D SOLD
1967 Dodge W200 B383, NP420/NP201 SOLD
1969 Dodge Polara 500 B383, A833 SOLD
1972 Ford F250 FE390, NP435/NP205 SOLD
1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
2009 Impala SS LS4 V8


RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...Please include at least the year and model in your threads. It'll be easier to answer your questions.
And please let us know if and how your repairs were successful.

Last edited by hatzie; Yesterday at 09:11 PM.
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Old 04-01-2020, 01:29 PM   #8
Matt Man
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Re: Electrical Help

Quote:
Originally Posted by hatzie View Post
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.
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86 c30 crew cab dually 454/400 4/6 drop SOLD 1-8-11
1981 chevy K10 shorty 350/350C 12bolt, 10bolt, NP208
4" lift 35's
4.10's Detroit locker/Truetrac
Vintage Air
67 GMC Stepside Straight six/3 on the tree "The Peach"

K10 build http://67-72chevytrucks.com/vboard/s...d.php?t=671934

The Peach build http://67-72chevytrucks.com/vboard/s...d.php?t=733903




Last edited by Matt Man; 04-01-2020 at 01:41 PM.
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Old 04-01-2020, 04:34 PM   #9
hatzie
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Re: Electrical Help

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.
__________________
1959 M35A2 LDT465-1D SOLD
1967 Dodge W200 B383, NP420/NP201 SOLD
1969 Dodge Polara 500 B383, A833 SOLD
1972 Ford F250 FE390, NP435/NP205 SOLD
1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
2009 Impala SS LS4 V8


RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...Please include at least the year and model in your threads. It'll be easier to answer your questions.
And please let us know if and how your repairs were successful.

Last edited by hatzie; 04-01-2020 at 04:49 PM.
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Old Yesterday, 12:33 PM   #10
Matt Man
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Re: Electrical Help

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!
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86 c30 crew cab dually 454/400 4/6 drop SOLD 1-8-11
1981 chevy K10 shorty 350/350C 12bolt, 10bolt, NP208
4" lift 35's
4.10's Detroit locker/Truetrac
Vintage Air
67 GMC Stepside Straight six/3 on the tree "The Peach"

K10 build http://67-72chevytrucks.com/vboard/s...d.php?t=671934

The Peach build http://67-72chevytrucks.com/vboard/s...d.php?t=733903



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Old Yesterday, 01:43 PM   #11
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Re: Electrical Help

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Old Yesterday, 09:20 PM   #12
hatzie
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Re: Electrical Help

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.
__________________
1959 M35A2 LDT465-1D SOLD
1967 Dodge W200 B383, NP420/NP201 SOLD
1969 Dodge Polara 500 B383, A833 SOLD
1972 Ford F250 FE390, NP435/NP205 SOLD
1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
2009 Impala SS LS4 V8


RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...Please include at least the year and model in your threads. It'll be easier to answer your questions.
And please let us know if and how your repairs were successful.
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Old Yesterday, 10:05 PM   #13
Matt Man
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Re: Electrical Help

Quote:
Originally Posted by hatzie View Post
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!
__________________
86 c30 crew cab dually 454/400 4/6 drop SOLD 1-8-11
1981 chevy K10 shorty 350/350C 12bolt, 10bolt, NP208
4" lift 35's
4.10's Detroit locker/Truetrac
Vintage Air
67 GMC Stepside Straight six/3 on the tree "The Peach"

K10 build http://67-72chevytrucks.com/vboard/s...d.php?t=671934

The Peach build http://67-72chevytrucks.com/vboard/s...d.php?t=733903



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