Charging issues with new cluster.

[Awann99]

I recently swapped my idiot light cluster for a 7 hole tac cluster on my 1969 gmc. ( the tac is busted so it’s not hooked up and there for show at the moment). I repinned the connector according to a post on here. But I did not add the two black wires for the #1 and #12 pin. I added a electric sender for the temp gauge. But it won’t read. It only comes in when I start the truck. It pins itself and then goes back to its lowest setting. Now the battery will not charge. I had the alternator tested and it is fine. But when I remove the battery cable the truck dies. I’ve checked the wiring and everything looks fine. Do the two black wires for the amp gauge need to be hooked up to charge the battery?
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[ray_mcavoy]

No, the two black wires do not have to be hooked up to the #1 & #12 pins for the battery to charge. Those wires are only necessary if you want to make the battery gauge functional.

The "GENERATOR" light that was in the old cluster was originally part of the alternator's "exciter" circuit that energizes the alternator's field when the ignition is on. You no longer have this light with the gauge cluster, but the wiring harness should still contain a special resistance wire (brown with white stripe) that was wired in parallel with that bulb and should still provide the necessary current to energize the alternator. Although if there is a problem with that wire (like a bad connection) it could be what is preventing the alternator from charging the battery.

As for the temp gauge pegging when you start the engine, that is due to the "bulb check" feature that was wired into the temperature warning light circuit. You can eliminate that by disconnecting the green wire from the back of the ignition switch (insulate the end so it doesn't short out on anything).

And for the temp gauge not reading, double check to be sure the new electric sender you installed is correct for the application.

[Steeveedee]

Like Roy says, the exciter wire may be the issue. Also, don't pull a battery cable off to check for charging, as it can cause a diode to pop in the alternator from the power surge.

[Awann99]

Originally Posted by ray_mcavoy

No, the two black wires do not have to be hooked up to the #1 & #12 pins for the battery to charge. Those wires are only necessary if you want to make the battery gauge functional.

The "GENERATOR" light that was in the old cluster was originally part of the alternator's "exciter" circuit that energizes the alternator's field when the ignition is on. You no longer have this light with the gauge cluster, but the wiring harness should still contain a special resistance wire (brown with white stripe) that was wired in parallel with that bulb and should still provide the necessary current to energize the alternator. Although if there is a problem with that wire (like a bad connection) it could be what is preventing the alternator from charging the battery.

As for the temp gauge pegging when you start the engine, that is due to the "bulb check" feature that was wired into the temperature warning light circuit. You can eliminate that by disconnecting the green wire from the back of the ignition switch (insulate the end so it doesn't short out on anything).

And for the temp gauge not reading, double check to be sure the new electric sender you installed is correct for the application.

That was it. Thank you for the advice. The truck is charging well now. The resistor wire was snipped by the previous owner.
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