Charging problems

[Kmohr]

Just bought a 78 Sierra grande and the voltage meter keeps jumping all over and lights keep going real dim, I assumed it was voltage regulator but it's built in the alternator so I replaced it and it does good as I drive but at idle it lowers down to like 11 on the meter is this normal? Thanks guys

 

[willybubba]

test it with a multimeter, your gauge might be off. if its accurate then check your idle speed it might be too low. i believe those trucks should idle around 600 when warm. cold idle is going to be around 900-1K

 

[Kmohr]

Tried that and the meter is pretty much dead on, the truck idles fine at like .5 rpm. The belt is tight and new alternator with built in regulator. Any other ideas?

 

[willybubba]

if the idle is correct, and the meter is accurate, and your alt has been checked and verified, then the only other problem could be bad wiring. remember just because an alt is new, never assume its working properly. i've been a manager at a few different auto parts stores and ive seen several come back, and several tested off the shelf that failed.

 

[Kmohr]

I'll pull the alt and take itbin and have them test it. Thanks for all the help will keep this updated