You mean; truck turns over. Will not run. But with ether it will turn over and then run?
Have you checked the voltage at the solenoid or tried to manually give power/ground to the solenoid for grid heater? Check your fuses?
Grid heater not functioning has nothing to do with having to use ether. But it would be better to use gas on a rag instead of ether.
Yes the relay works, never sees 12 volts to coil. Manually energized it operates with no problems. All fuses good.
Maybe the cable from the grid heater to the solenoid is burnt or has a break?
I read it as if you manual engage the relay the heater will work, which would say the cables to the grid heater are ok.
Wonder if you have a dirty air temp sensor?