1972 K5 Electrical Issues

Captain Dave

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My new alternator does not charge the battery. The wiring looks suspicious to me. the four into one connection does not look right. one lead is output from the alternator. one is a jumper back to the voltage regulator and the third is the lead over to the battery. and there is a black wire with a fuse. It doesn't look right.

please share what you know.

CD

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6872xtc

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The splice of the red wires looks factory to me. It should have been covered in a decent layer of tape. The factory stuff was thick.
The small fuse is only for the shunt wire to the ammeter in the dash. There is one on each side of the radiator support at the corner, near the fender. It should still charge with those fuses blown, or missing, but it won't show on the ammeter. At least that's what I remember. Been a while since I had to troubleshoot one.
 

bp71k5

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The splice of the red wires looks factory to me. It should have been covered in a decent layer of tape. The factory stuff was thick.
The small fuse is only for the shunt wire to the ammeter in the dash. There is one on each side of the radiator support at the corner, near the fender. It should still charge with those fuses blown, or missing, but it won't show on the ammeter. At least that's what I remember. Been a while since I had to troubleshoot one.

x2
 

500$k5

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Exactly what @6872xtc said. is all factory, and correct. Just missing the factory tape. Tell me what is going on, what alternator you have, past problems, etc. We'll try to diag for you.
 

Captain Dave

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The battery is not getting a charge. So I took the battery and alternator in and had them tested. Batt was OK. Alt was not. I replaced the alternator but it didn't solve the problem. The voltage across the battery terminals is the same when the engine is running or not. I have pulled everything apart looking for bare wires and have redone a couple of connections. No luck so far. I have an external voltage regulator. The alternator has a red power wire and smaller blue and white wires that go to the voltage regulator. Any help would be welcome.
 

bp71k5

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The battery is not getting a charge. So I took the battery and alternator in and had them tested. Batt was OK. Alt was not. I replaced the alternator but it didn't solve the problem. The voltage across the battery terminals is the same when the engine is running or not. I have pulled everything apart looking for bare wires and have redone a couple of connections. No luck so far. I have an external voltage regulator. The alternator has a red power wire and smaller blue and white wires that go to the voltage regulator. Any help would be welcome.

have you replaced the voltage regulator? Curious why you didn’t switch to internally regulated alternator?
 

diesel4me

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Check for power at the 2 prong plug on the alt,it should have 12V on both wires while running..
I've had issues with 3 of the first gen GM''s I had,the tan wire coming from the fuse block to the #2 terminal on the alt plug was rotted and no power would get to it consistently--without that wire sending 12V from the ignition,the field coils will not be energized and it wont make a charge...

A quick test can be done by watching the voltmeter with it running,jump across both wires on that plug,you may heard the alt "kick in" and start charging ,and show up on the voltmeter..

I had to run a new wire from the fuse box on my trucks to get them to charge consistently--some days it'd charge fine,others the battery ran down,and I had replaced the alt and voltage regulator for nothing !..

It is pretty simple to upgrade to an integral regulator alt on these trucks.its a step up from the old external regulators ,which are prone to fail rather easily..
 

500$k5

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Check for power at the 2 prong plug on the alt,it should have 12V on both wires while running..
I've had issues with 3 of the first gen GM''s I had,the tan wire coming from the fuse block to the #2 terminal on the alt plug was rotted and no power would get to it consistently--without that wire sending 12V from the ignition,the field coils will not be energized and it wont make a charge...

A quick test can be done by watching the voltmeter with it running,jump across both wires on that plug,you may heard the alt "kick in" and start charging ,and show up on the voltmeter..

I had to run a new wire from the fuse box on my trucks to get them to charge consistently--some days it'd charge fine,others the battery ran down,and I had replaced the alt and voltage regulator for nothing !..

It is pretty simple to upgrade to an integral regulator alt on these trucks.its a step up from the old external regulators ,which are prone to fail rather easily..
Gen 1, external voltage regulator trucks do not have a tan wire to the alt. They have a blue wire, which runs from the regulator field terminal, to the alternator field (F) terminal. The have a white wire running from the stator terminal on the regulator, to the stator (R) terminal on the alternator. The regulator has 4 terminals, marked F,2,3,4. F is field, which is a variable positive voltage to the alternator field. 2 is the stator terminal, which is a positive ac signal from the alternator, back to the regulator. 3 is a switched positive signal, from the ignition switch, to turn the regulator on. 4 is a full time battery voltage, from the truck, to the voltage regulator. Its usually tied to the bus bar on the horn relay.
 
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500$k5

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The only thing I see on your pics, that isn't right, is the circuit breaker, in the main feed wire. That would have been a insulated terminal block, with a fuse link going to the battery. The circuit breaker is ok, if it is big enough to carry the charge current, and also if it is still good.
 

bp71k5

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The only thing I see on your pics, that isn't right, is the circuit breaker, in the main feed wire. That would have been a insulated terminal block, with a fuse link going to the battery. The circuit breaker is ok, if it is big enough to carry the charge current, and also if it is still good.
I’d ditch the circuit breaker. The charge wire should be a straight solid connection (ie no resetting circuits messing with the charge current). I have my main power lug fused with a 150amp maxi fuse instead, do they even make those little circuit breakers at more than 40 amps?
 
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