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I just put head gaskets and a head on an 89 f250 with a 7.3 and a 5spd. ive been driving it around for about a week now and everything worked good then the temp guage (original) just went to reading hot even after the truck was first started. Then a couple days later the alternator wont fully charge it just stays on the low side. Is The voltage regulator bad? Thanks Justin
Find the temp sensor on the engine(it's on one of the front corners?) and should have a red/white or a white/red wire on it. Turn the key to run and get someone to watch the temp gauge as you take the wire off the sending unit and ground it to the block. Then take the wire off ground and let it hang in the air. Every time you do this, the gauge should swing full scale back and forth. If it does, then the gauge and wiring is good, and the sending unit is bad.
Try removing and replacing the wire on the temp sensor.
Did you use teflon tape when you reinstalled the temp sensor?
Check the wiring on the alternator.
Do be careful when you check the output terminal, it has battery voltage on it at all times.
The plug in connector may have a bit of corrosion in the terminals which will affect the charge rate.