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service truck issues

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chris_james

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Aug 26, 2015
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84
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Ga
Greetings. Im have an issue with my service truck its a 1995 GMC Topkick. The intake heater went out. So I tested the solenoid I had power going to it non coming out. So I replaced it the problem continued. Went back dubble check fusse are still good. So what im hoping for is that some one here may have service manual for this truck or atlest a wire digram because I have neither for the truck.
 
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Delmer

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Jan 3, 2013
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8,891
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WI
So you still don't have power coming out of the solenoid/relay? I had one with a loose connection at the heater, but you'd be able to trace that to power to the wire but not on the stud. Need a helper to turn the key on and off to test.

What temperatures do you have there? you need the intake heater to start it? Does it blow white smoke when cranking and not starting?
 
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Wes J

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Jan 24, 2016
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Peoria, IL
The solenoid should have 4 wires. The high amp side should have power on one side all the time and power at the other side with the solenoid is "on". The other two wires activate the coil in the solenoid. One of those should short to ground. The other gets power from whatever switch activates the solenoid. There may be a relay in that circuit or some kind of timer, I really don't know.

If you replaced the solenoid and it still won't switch, it seems like the problem is in the coil side of the circuit. It should be pretty easy to track down.
 
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chris_james

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Aug 26, 2015
Messages
84
Location
Ga
Sorry about the delay I got deathy ill about not long after posting. Ok so I have continuity on the coil side. I have 12 vots on the post coming into to the solenoid as well as 12 vots in the plug on wire when the key is truned on. So im still at a loss
 
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chris_james

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Aug 26, 2015
Messages
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Location
Ga
Also yes white smoke the temp out has been around 25-35. Also light on the dash for the intake heater isnt working bulb is good.
 
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Wes J

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Just rig up your remote start switch to the coil side of the solenoid and see if you can make it fire. If you can, it's a wiring issue on the coil side. If not, the solenoid is still bad.
 
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chris_james

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Aug 26, 2015
Messages
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Ga
Ok so if I run a jumper wire the heater works. I have yet to figure out where my short is going to the solenoid because when the wires inter the cab they change colors. And without a wirer digram im sol. Yeah still working on this it warmed up and the yellow stuff went down got put on back burner
 
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chris_james

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Aug 26, 2015
Messages
84
Location
Ga
From the hot side of solenoid to the heater. Found my issue not getting a ground to the solenoid. Stuck my testlight with a bigger groundwire into the wire thats suppose to be the ground to grounded the wire and the solenoid clicked. Now to just find the short.
 
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Wes J

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Sometimes it's easier to just cut the wires and run a couple new ones. Who knows who did what under that dash on that old rig.
 
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chris_james

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Aug 26, 2015
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Ga
Ive heard stories about a crackhead rewiring years ago with speaker wire. My blower motor for ac/heat gets trun on by a riggef up toggle switch
 
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chris_james

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Aug 26, 2015
Messages
84
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Ga
Ok so im still at this. So I follow the ground wire for the intake heater solenoid to the instrument cluster. Once you unplug the cluster my ground becomes a ground again I know longer have power running threw it. To me it sounds like my short s the cluster. Any thoughts?
 
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Delmer

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You have an indicator light for the heater on the instrument cluster, that could be where the "open circuit" is, and that's probably why the ground wire goes back to the instrument cluster?

Have you checked to see what happens if you ground that side of the solenoid? Does the heater shut off after 30 seconds or whatever? I'd rather have the heater working than the indicator light telling me for sure that it's not working.

An "open circuit" carries no current, a "short" usually blows a fuse.
 
Last edited:
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chris_james

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Aug 26, 2015
Messages
84
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Ga
Yes it goes to an indicater light. When I ground it to the solenoid side the solenoid works.
 
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Jonas302

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Jan 4, 2015
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mn
Pm email I scanned the pages out of the manual but they are the wrong format to post
 
Mobiltech

Mobiltech

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I am guessing you have a cat engine in this truck . It would be good to post the engine serial number.
The intake heater is probably grounded by the engine ecm to turn on the heater. If you post a serial number we can get you a schematic.
 
Mobiltech

Mobiltech

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If its a 3116 it will probably have a rectangular box on the drivers side of the engine that is the heater timer module. It senses engine temp and cycles the heater.
 
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