air intake preheater stopped working- 1991 w250

[steve jupiter]

a few months ago, i had to replace the battery on my 1991 w250. ever since i put the new battery in, i have had no air intake preheat. still starts, but it does not get too cold (30's) here. i suspect relays (no buzzing or clicks), engine control module, thermister, or failed heater element. i never had a problem with the air intake preheater since i bought the truck new. i would like to know what sequence these possibilities should be checked, and have i missed something else ?