CUMMINGS 370 PRE HEAT-gctid823826

[Boreal]

I replaced a dead alternator and the preheat light will not shut off and the preheat itself appears to not be working at all. Any suggestions?

[The_Other_Gary]

The preheat circuits and the alternator circuits are separate. check the plug in on top of the Alternator if it is a Delco.

check the 2 contactors on the preheat system as they are prone to failure and check that there is power to the preheat ECM.

https://www.sbmar.com/wp-content/uploads/2015/11/B-C-wiring1.pdf

Note the several alternator wiring options by brand.

Here is the Air Heater diagram

https://www.sbmar.com/wp-content/uploads/2015/11/B-C-wiring.pdf