I have an 89 7.3 and previous owner wired a button on the dash that grounds one pole on the glowplug controller for manual heating. Crazy thing is: None of the manuals mention a manual controller, or even one that uses glow-plug resistance; Ford manual shows circuit using engine temp switch and fuel line heater for ground side of wait-to-start bulb..

I've attached pictures of my controller, and the Ford manual circuit. how to tell if it's got the auto sensing wiring?

You'll notice button wire and wait to start wire(red on mine) on same pole below starter relay pole(10ga yellow), mysterious yellow wire on plug pole(10ga brown), and additional red wire on fuel shutoff solenoid pole. Anything without black shrink-boot isn't factory.

 

"Ford manual shows circuit using engine temp switch and fuel line heater for ground side of wait-to-start bulb"

Actually No that is the Hot side of the Lamp and the engine temp sensor and heater have nothing to do with Glow plug system function other than be a Common HOT point for the Lamp.


the controller uses the shunt to monitor current and also has a Thermistor inside the controller to monitor controller temp.
the plugs are PTC

 

Will this help?

https://www.ford-trucks.com/forums/5...low-plugs.html


Charlie

 

seems to me it already has the Switch installed... what I would do is just disconnect the wire from the controller to the relay shown in the the original pictures.

I think that is the Red wire on the Right side... then the other wire goes to the switch which Grounds the Relay Coil.

the reason you disconnect the controller is so if it shorts then it will not hold the Relay closed and Fry the Glow Plugs.

One should also use a Freewheeling Diode to prevent Arcing in the Push Button switch.

 

I'm assuming this would make it last alot longer, because I don't get much life out of push buttons these days, nor toggle switches.

 

This ^^^^^^^^^^ exactly. especially when using the Stancor Relays, it stops the inductive kick back when the switch is disengaged (Back EMF causes Arc)

 

Yeah that back emf has bitten me a time or two

But I'll look into those diodes and probably order some

 

I use a 1n4007 very common and I've yet to have one fail. it's a 1 Amp ... a 1n5408 would be a good choice too 3 Amp.

 

I have a bag of both actually, when you said free wheeling I thought you meant something more special.

 

Free Wheeling or Flyback is just terms used.... BTW I use em on the starter relays too .... to prevent premature ignition switch failure

Diodes are cheap and all relays should be protected

 

Great idea with the starter solenoid/relay