I have a '71 Cutlass Supreme. The generator light will faintly come on and buzz, but only when engine is at low RPM. No issues while cruising, only when slowing or stopped. New battery, alternator and voltage regulator. Thanks for any advice.

 

Welcome to CO, first thing to check is make sure the belt is tight.

 

It seemed pretty tight, will check again though, thanks Chris.

 

try a solid state regulator. less expensive than the mechanical ones.

 

Trouble shoot before throwing parts at it.
Remember new doesn't mean good.
What is the charging voltage?
Whats is the surface charge on the battery?
Are the battery cables clean and tight on both ends? Check both secondary wires for high resistance (battery cables).
Clean grounds are your friend with a negative ground system such as is seen on your 71.
The buzz would make me suspicious of the regulator. Especially if its offshore. It needs a good ground too. As suggested if it is bad invest in a solid state unit. Your OEM lid can be affixed to the solid state unit to make it look factory. Dont toss the OEM. Those lids are nice to have.

Sounds like you have an external regulator? If so the light is fed from the regulator connector on the firewall terminal #4, brown wire. The brown wire goes through the bulkhead connector and then directly to the light. On the other side is a pink wire that also feeds power to your fuel gauge, temp light, parking brake light, and oil pressure light. So depending on which side of the light is low (brown or pink wire to ground) that will be the direction you need to go.

Again, verify all negatives(grounds) are clean and tight. Look for a bad connector.

A loose belt would more likely show up during WOT acceleration.

For an Internally regulated alternator the bulb is supplied with +12v with the key in the RUN position. The other side of the bulb is connected to the #1 terminal on the alternator (assuming a three wire, internal regulator alt, like the SI-family). In the regulator, the #1 terminal is grounded when the alt output is low and should be full alt voltage when the alt is charging. By having the same voltage on both sides of the bulb, it does not illuminate. If voltage on one side (and it could be either side) is low, current flows through the filament and the bulb starts to glow. The greater the voltage differential, the brighter the bulb. If the bulb is glowing dimly, you have a voltage drop on one side of the bulb. Start by checking output voltage at the #1 terminal on the alternator - it should be 13.8V or so. If you can get to the IP connector or the two terminals of the bulb socket, check the voltage of each of those to ground with the engine running. They should be the same. If one is lower, find the voltage drop in that wire. It will likely be a dirty connector terminal someplace.

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One thing to verify is there should be a star washer at one of the regulator mounting points, between the regulator body and the firewall. This helps ensure a good ground to the firewall.

 

[QUOTE=droldsmorland;1113197]Trouble shoot before throwing parts at it.
Remember new doesn't mean good.
What is the charging voltage?
Whats is the surface charge on the battery?
Are the battery cables clean and tight on both ends? Check both secondary wires for high resistance (battery cables).
Clean grounds are your friend with a negative ground system such as is seen on your 71.
The buzz would make me suspicious of the regulator. Especially if its offshore. It needs a good ground too. As suggested if it is bad invest in a solid state unit. Your OEM lid can be affixed to the solid state unit to make it look factory. Dont toss the OEM. Those lids are nice to have.

Sounds like you have an external regulator? If so the light is fed from the regulator connector on the firewall terminal #4, brown wire. The brown wire goes through the bulkhead connector and then directly to the light. On the other side is a pink wire that also feeds power to your fuel gauge, temp light, parking brake light, and oil pressure light. So depending on which side of the light is low (brown or pink wire to ground) that will be the direction you need to go.

Again, verify all negatives(grounds) are clean and tight. Look for a bad connector.

A loose belt would more likely show up during WOT acceleration.

For an Internally regulated alternator the bulb is supplied with +12v with the key in the RUN position. The other side of the bulb is connected to the #1 terminal on the alternator (assuming a three wire, internal regulator alt, like the SI-family). In the regulator, the #1 terminal is grounded when the alt output is low and should be full alt voltage when the alt is charging. By having the same voltage on both sides of the bulb, it does not illuminate. If voltage on one side (and it could be either side) is low, current flows through the filament and the bulb starts to glow. The greater the voltage differential, the brighter the bulb. If the bulb is glowing dimly, you have a voltage drop on one side of the bulb. Start by checking output voltage at the #1 terminal on the alternator - it should be 13.8V or so. If you can get to the IP connector or the two terminals of the bulb socket, check the voltage of each of those to ground with the engine running. They should be the same. If one is lower, find the voltage drop in that wire. It will likely be a dirty connector terminal someplace.

Wow, that was a very in depth reply, thanks for your time.