Alternator Noise

[Rustbucket350]

My alternator makes a wicked squeal on startup and chirps once I start driving. I replaced it with a new alternator and I get the same noise. I did find the plug was bad so I replaced it with a new one as well which eliminated most of the squealing. I'm wondering if the voltage regulator may be fried already by the old plug shorting the terminals out. I have the main lug wired to the battery side of the starter solenoid, the voltage sensor to the back of the alternator (solenoid lug), the stator in the middle obviously plugs into the single terminal on the side, and the exciter wired to the ignition cylinder in the key on accessory position. Is my wiring right at least? I know it's the alternator because I can unplug it and the noise disappears even with the belt on. I do have 14.5 volts on the battery at idle.

 

[RonD]

3 wire connector will have light Green wire that is the ON/OFF switch for alternator, it runs to the Battery Light in dash, key on powers the battery light bulb and when alternator is not spinning it is at 0volts(ground) so Battery light is on
When alternator starts to work, above 12volts, the Battery light goes off because both wires on bulb are the same voltage.
(if alternator stops working or voltage drops below battery voltage, 12volts, then battery light comes on or flickers because of the lower voltage on one side of bulb)

Yellow wire should have battery voltage all the time, key on or off won't matter, it is a fused wire, usually 15amp in engine fuse box(ALT), but can also be Fusible link

B+ wire on back of alternator should also have battery voltage 24/7, all the time, and uses either a MEGA fuse or fusible links(usually 2)

Yes, it reads like you are getting arcing inside alternator.
Yes, could be voltage regulator.

Voltage regulator is there to adjust alternator output so battery isn't "cooked", chemicals boiled away.
Couple of tests you can do to see if it is working
Right after startup voltage regulator will output 14+ volts to quickly recharge battery, after a few minutes that voltage should drop to under 14volts, 13.5v approx., that prevents battery from boiling.
Also the voltage regulator reacts to electrical draw from truck electrics, if you turn on head lights you should see voltage drop then come back up as voltage regulator responds to power draw, same if you turn Fan to High

 

[Rustbucket350]

Haha it was the belt after all. Sprayed a liberal amount of belt conditioner on it and it went right away. I should have done that first thing.

 

[RonD]

Good work

That would explain why disconnecting 3 wire connector stopped the noise, alternator shut off so no load and no slip.

Just a heads up.
When a fan belt starts to slip it causes glazing on the pulleys it is slipping on.
Fan belts operate on friction, a good grip, glazed areas are like ice, so lack a good grip
This is why replacing a slipping fan belt makes for less slipping but not all slipping.
And why belt spray works but then stops working and you have to spray belt again.

Once you have fan belt slipping it is best to remove belt and then either rough up pulley surfaces, Emory cloth, or paint pulley surfaces, this removes or covers up the gazed areas and gets good grip back.
Up to you whether or not you replace the belt and/or tensioner at that time.

 

[Rustbucket350]

I may have to either find a shorter belt or rough the pulleys up like you said. The water pump pulley isn't factory so I had to get a longer belt. It wasn't quite as tight as I would have liked but it wasn't a problem til it started slipping.