Voltage Drop

[TxFiddler]

What causes the voltage on the guage to drop when the blower fan is on high at engine idle?  Also, the pwr windows operate slowly when the fan is on high and the headlights dim.  Would a new alternator correct this?  Possibly a 100 amp?  Thanks.

[jaredts]

There may be other things to consider, but here are a couple:  Make sure your idle speed isn't set too low, and make sure you have all the required grounds (in good condition) especially from the engine to firewall and battery to radiator support.  Some dimming of headlights and slow windows should be expected, but should be minor.  If everything's in good shape a bigger alternator should help, but again isn't normally required.

[TxFiddler]

Hey thanks jared.  I'll check out the connections and see if it helps.  Probably some corrosion since the truck is ONLY 30 yrs old.

[jaredts]

Longest lasting trucks on the road!   

[Irish_Alley]

Give some numbers ex. Volts before and after and rpms

[TxFiddler]

Irish, just going by the guage, normal reading is just a hair passed the 13.  Especially on a hot, Texas day, at idle with blower on high, the guage is almost, but not quite touching the red on the low side.  I dont have specific readings, just whatever the guage reads. Thanks.

[Irish_Alley]

Norm should be around 14-16 if you have a volt tester just put it on the battery and see what it says. Also sounds like a week alt I would take the whole truck to auto/advanced and get them to do a charging system test on it. make sure your battery connections are clean and tight