1989 D250 when the engine is reved up the alt. is putting 18 volts into the battery.I took the voltage regulator off and it tested ok.with the truck just idling it only puts 13.5volts into the battery.Any suggestions? When driving the truck the high output of the alternator is cooking my battery.

 

thats normal, most charge at about 14v, which your at

 

at higher RPMs the alt should have a higfher AMP output and a bit more Voltage output.

my 93 D250 had a fluxuating alt charge do to a faulty wire in the harness that had been cut and replaced with an inline fuse prior to my ownership...ended up melting the fuse holder 1 night and the truck would not even light the dash...[:@]

 

Hmm... I have the opposite problem.. My work truck... A ****ernational... Reads under 14 at idle... still under 14 at full RPM... wonder how you guys get soo much....