1999 ford super duty relay coil keeps blowing fuse. truck wont start. why?

Double check "trigger" wiring from the solenoid back to switch, perhaps a power relay in between that might be bad. I'd polish to bright metal that old connection to the solinoid.

Does it start when the outside temp is above freezing? if so then start with the relay also check the engine codes. Disconnect the negative terminal for 30 minutes. This will reset the diagnostic computer. Reconnect and attempt to start as usual.

Sounds like a glow plug issue. The glow plug relay located on the top of the engine near the fuel filter is a common cause of the problem.

replace the relay for the glow plugs,its expensive

bad glow plugs or fuses is pop or they are working and afew are working you chould plug in the heater to atnight time there is a 120 plug on the truck usely driver side or infront of truck

is it the crank fuse if it is could be starter drawing to many amps try new starter

that will more than likely be the glow plug feuse,check for any visible burnt wires, or possibly a grounde glow plug

It is the fuel heater, All you have to do is unplug it.

Replace the glowplug relay.Its faulty.The glow plugs stay on until engine warms up.The engine temp switch then activates the relay to switch off.So it could be the temp switch also faulty.

It is most likely fuel heater in bottom of filter housing. Unplug it on backside of housing and reinstall good fuse and see if it quits blowing. If so, updated fuel heater availible through Ford.