Can anyone tell me; 1) How to tell the GP Controller is bad. 2) If it is bad can it just be bypassed? If I install a manual button, why is a controller needed?

My GP's suddenly quit working. I have gone throught the system replacing the relay and so far as tracing wires to find barespots/grounds etc and I just can't find anything wrong. Lost.

I have a 1982 blazer and I guess the controllers are notoriously unreliable, I
bypassed mine, I just unhooked it where it hooks to the controller on the engine,
tied the harness up out of the way, there are two small wires the go to the GP solenoid
all you have to do is run a wire to a switch that grounds one of those wires, so instead of power to the switch you ground it out when you flip it be sure and get a switch that goes off when you let off it.(spring loaded self centering type)

on mine its the green wire, I left everything hooked up except the controller, all I did was put one of those crimp on wire connectors the open ended kind for a screw terminal (looks like a two pronged fork) on the end of the wire coming from my new switch and stuffed it in with the the connector with the green wire on the solenoid,

I really like having it this way because once the engine is warm you don't need the GP's and you never have to wait to start it

I might add that when I bypassed mine it was still working but was coming on even with the engine warm, yours just went out so might be something else that even when you perform a bypass it wont work.

Mine started cycling on with the engine warm awhile back, not very often but just once in a while. Didin't hurt the glow plugs but obviously a controller problem.

Is that wire you hooked into one of the ones that go to one of the prongs on the relay? The one without power with the ignition on?

yes I think thats the one

easy way to find it unhook the controller, unhook one of you GP wires and hook a test light to it, take a wire and ground it, turn the key on, touch the grounded wire to the wire thats not hot when the key is on and watch your test light if it lights up then thats it, on mine the glow plug light on the dash lights up up too.