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Ask Jared D Your Own Question
Jared D
Jared D, ASE Certified Technician
Category: Chevy
Satisfied Customers: 1349
Experience:  Shop Supervisor at County Fleet
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The glow plugs in my 86 chevy k-10 will not come on,unless I

Customer Question

the glow plugs in my 86 chevy k-10 will not come on,unless I plug in block heater for 4 or more hours.i have replaced glow plug controller and it didn't make a difference.i have heard it might be the glow plug sensor also called inhibit switch.whatcha think?
Submitted: 1 year ago.
Category: Chevy
Expert:  Jared D replied 1 year ago.

I think you are probably on the right track about the glow plug sensor (the plug power feedback), but it could also be the glow plug controller. Here is the procedure for checking the glow plug system for a fault:

1. Disconnect each glow plug electrical connector. Be careful not to snap off the spade soldered on the glow plug.

2. Verify a conventional test light from B+ lights when the tip is placed on each glow plug.

3. If a glow plug has to be replaced, remove the old glow plug carefully. The tips can break off inside the engine.

4. Disconnect the round glow plug controller screwed into the top of the engine.

5. On the harness side, ground the Blue wire, pin 3 for no more than 2-3 seconds. The glow plug relay should "click" and the glow plugs should have battery voltage applied.

6. Verify that both Black wires in pins 5 and 6 go to a good ground.

7. Verify that the Orange wire (1982) or Dark Green wire (1983-1984) has battery power when the Blue wire in pin 3 is grounded. This is the glow plug power feedback to the controller. Note that pin 2 is not used and is usually plugged off.

8. The Brown wire in pin 1 is connected to the alternator indicator bulb in the dash and should measure about 1-2 volts Key On Engine Off (KOEO) and about battery voltage with the engine running.

9. If all OK, replace the glow plug controller.

Expert:  Jared D replied 1 year ago.

This sequence is more specific to your year model. The other one was for 82-84.

1. Connect a test light from ground to one of the glow plug wires.

2. With initial key ON, the WAIT lamp should be ON at the Instrument Panel Cluster (IPC) and the test light should light bright at the glow plug.

3. If the test light does not light, check glow plug relay operation.

4. The Pink/Black wire at the relay should have 12 V with key ON.

5. The Light Blue wire should indicate a ground signal from the glow plug module anytime that the WAIT lamp is ON.

6. If the Pink/Black is near 12 V and the Light Blue is a ground, then the glow plug relay should "click" and the relay should route 12 V from the B+ stud, Red wire, on the relay to the outgoing stud, Orange wire, to the glow plugs.

7. If the glow plug does have a bright test light, then check the DC voltage at the glow plug when it's activated. Test all 8 glow plugs connected.

8. The DC voltage at any one glow plug should be close to 12 V.

9. If higher than 15 V, suspect open glow plugs.

10. If lower than 12 V with relay ON, test voltage into the relay on the Red wire.

11. If OK on Red, but low voltage on the Orange wire while the relay is ON, suspect a faulty glow plug relay or glow plug relay connection.

12. If the voltage is low on the Red wire to the glow plug relay while the system is ON, suspect that one of the two glow plug resistors are open.

Customer: replied 1 year ago.
the wait light does not come on at all.is the glow plug relay the same as glow plug controller?
Expert:  Jared D replied 1 year ago.

No, they are two separate parts. I'm trying to get you a location diagram of the entire system but because of the year model there isn't much available anymore. The glow plug relay will be in the relay junction box, I just can't find a listing for which one it is.

Expert:  Jared D replied 1 year ago.

I'm sorry, AllData, Identifix and Motor don't list any diagrams other than the glow plug control module. You will have to look through your relays in the fuse/junction box to find the glow plug relay location.

Customer: replied 1 year ago.
is the relay junction box under the hood or under the dash?
Expert:  Jared D replied 1 year ago.

I have an 86 chevy c10 outside, but it's a gas engine. I'll go look and see if I can see a spot for the glow plug relay. Sometimes chevy used the same box on the gas and diesel trucks.

Expert:  Jared D replied 1 year ago.

There is a small relay junction box to the right of the steering column under the dash. I would check there. I couldn't see anywhere else that might house a relay, if the diesel version uses the same fuse block.

Expert:  Jared D replied 1 year ago.

Check for a fender mounted solenoid style relay. Like this one.

Expert:  Jared D replied 1 year ago.

Driver's side fender.

Expert:  Jared D replied 1 year ago.

Yeah, I'm positive that's the style of relay on this year of truck. It's mounted on the fender. I can see the holes where it would mount on my truck (if it was a diesel).

To test it use a jumper wire from the positive battery terminal to the small connector on the relay. Use a test light or a voltmeter touching the terminal leading to the glow plugs to see if power is traveling through the relay when you activate it with the jumper. This might be easier with two people.

Customer: replied 1 year ago.
i dont see a solenoid that style any where on this truck.also the block heater that fastens to one of the freeze plugs is shorted out.can u tell me how to remove block heater?
Customer: replied 1 year ago.
hey man i found relay block right of steering column like you said!there r three relays.one looks like its just a buzzer.one looks like a turn signal relay.you think the last one is my problem?
Expert:  Jared D replied 1 year ago.

I think the last one is the headlight relay. I'm starting to think that this year model incorporated the relay and glow plug controller in one unit. This is what the controller looks like and I'm pretty sure it acts like a relay as well. In the earlier models there is a separate solenoid on the fender. I'm sorry I have to piece together info on this one. There really is nothing in the way of reference material out there.

Customer: replied 1 year ago.
yeah,the three were buzzer,hazard and horn.i replaced the controller and nothing changed.to me its strange that pluging in block heater would make WAIT light up and glow plugs work.maybe i got a bad controller?im pretty much out of ideas.also im getting 12 volts between the large wires on controller with ignition key off.does that seem right?thanks for your help.nobody seems to know much about this issue.
Expert:  Jared D replied 1 year ago.

12 volts on the controller sound normal with key off. Then there should be a circuit that send that 12 volts to the glow plugs with key on.

Is it possible that the block heater is somehow wired in so that it is cutting power to the controller? Is it a factory block heater or something that has been added in?

Customer: replied 1 year ago.
that controller is exactly what i have.the block heater is factory and is either attached to,or part of a freeze plug on left side of engine.it is not wired in to controller.however before the heater burnt up,the WAIT light would come on as well as glow plugs and engine would start and run fine.there must be some type of block heat sensor i`m thinking is not working properly.
Expert:  Jared D replied 1 year ago.

I still think either the block heater is messing something up or it is providing a ground somewhere. The wait light should be on a timer and should illuminate for a few seconds or voltage to the controller and then go out. The block heater shouldn't affect it at all. If it is, the block heater is acting up somehow. There are two styles of freeze plug block heaters on this truck. One has a small jamb nut on the outside of the plug which you loosen and the plug will pry out. The other style just presses in like a freeze plug and you basically just pry it out. You can use a chisel to knock it sideways so you can get a grip on it with some vice-grips and then pull it out.

Expert:  Jared D replied 1 year ago.

I just wanted to check and see if you need any additional information. Also, if I have been of some assistance I would appreciate a positive rating. Thanks!