ALT Pully size ?

[n1265]

I am having problems with headlight flair on my 1977 M880, I also have a definate increase to the blower motor rpm when stepping on the gas. I have lived with this for the past few years and have changed out the ALT and voltage reg. I have also temporarly bypassed the AMP gauge with a 1/4 in. bolt but it has made no difference. The truck idles at 760 rpms.

Now I am wondering if I have the right size pulley on the newer ALT. I dont remember changing it or even looking to make sure it was the same size as the one I took off.

the pully is about 2 3/4 in. in Dia.

Thanks,

[712edf]

Going to a smaller alternator pulley (if one exists) would increasealternator rpm's & maybe fix your problem.
How is all your cables & overall wiring? Corrosion & resistance may cause similar symptoms. Also the more ground straps you have on this truck the better.

Bucky

[n1265]

I can not find a problem with the wires or connections, but the ground straps I have not checked, except for :

1) Neg battery cable to motor
2) ground wire to driver side fender
3 ) ground wires for the head lites on radiator supports
4) ground wire for insterment cluster

where are these ground straps that you are talking about suppose to be located ?

[712edf]

Sounds like you have located most, but seems like certain years would have them going from frame to the cab & bed. This aren't necessarily a dealbreaker if they aren't there, but the better connected to ground everything is, the better your circuit will be. Lights ground to fender or core support, which should be grounded to the frame, which should be grounded to the engine, which is grounded to the "-" post of battery. Since most of the drivetrain/suspension components have rubber/polyurethane between them & the frame, straps help with continuity between frame & engine & body.

Bucky

[n1265]

would 12 ga. wire be big enough to run from the cab and bed to the frame ?

or would I need something bigger ?

[n1265]

The red and green wires that lead to the ALT ( Field ? ) Does it matter what side they clip onto the ALT ? Are they reversiable ?

[USN78W150]

The wires are connection specific. With the truck off, connect a volt meter across the battery terminals. Read the voltage. Start the engine and read the voltage again. If the reading is the same or less, you are not charging. The small alternator wires, if hooked up backwards, will not let the truck charge. I believe the red wire is connected to the lead closest to the black 10 ga. wire, and the green to the other connection.