The heater won't work on my 89 E-350, fuse is ok, no power at the switch on the dash. Could it be the heater relay? if it is anyone know where it's located?

p.s. thank you "subford" for the fuse diagram

 

This is just FWIW until somebody smarter chimes in. I think you mean the _fan_ won't work? You've checked the wiring under the dash and no loose ends, right?. IRC there's a resistor pack in or on the fan enclosure on the passenger side in the engine compartment; I think it's more or less accessible. A manual with the electrical schematic would show how it's (supposed to be) wired and what else is in that circuit.

Sorry I can't more specific - been a while.

Rufus