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  #1  
Old March 9th, 2016, 10:50 AM
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Electrical Mystery Seeking Solution

Had an experience this morning that supports my long running theory that electronic circuitry is based on Black Magic rather than on science.

My wife called me a few minutes ago from a grocery store parking lot and told me that our 110 would not turn over. Earlier today she had shut it down / restarted at least 4 or 5 times without a problem. I had her check the coil wires and try a bunch of other things to no avail. Finally I asked her: have you used / changed anything since it last started: “yes … I turned the heater blower off”. She turned the blower back on and the engine tuned over on the first try.

So in summary: heater motor off = no start; heater motor on = start no problem. She verified this by trying it a few more times.

Is this happening because our electrical voodoo mojo is just lacking today? Or is it possible that our heater switch commandeered control of the coil over the course of the winter? Any ideas that don’t involve sacrificing the family pet, self flagellation or handling snakes would be greatly appreciated (I tried all those with my last electrical problem and none of them work).

One possible clue for any believers in electrical science: the roads are wet today so wires are likely wet too.
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  #2  
Old March 9th, 2016, 10:57 AM
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Obviously, the heater blower was supplying the necessary air to keep the Lucas fire burning.... without it= no start!


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  #3  
Old March 9th, 2016, 10:58 AM
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check all of your grounds, behind the dash and fuse box and make sure the engine block/starter are well grounded also.
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  #4  
Old March 9th, 2016, 11:02 AM
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Quote:
Originally Posted by Ren Ching View Post
check all of your grounds, behind the dash and fuse box and make sure the engine block/starter are well grounded also.
Exactly. It sounds like the ignition switch is grounding thru the heater.
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  #5  
Old March 9th, 2016, 11:05 AM
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Do you have a "normal" heater with the fan speed controlled by the lever on the side of the binnacle? It switches the ground side of the fan motor, so that would be pretty damn weird.

You say "not turn over". That means no starter action... But then you talk about the coil..... So, is it cranking but not firing or not cranking?
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  #6  
Old March 9th, 2016, 11:09 AM
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Quote:
Originally Posted by javelinadave View Post
Exactly. It sounds like the ignition switch is grounding thru the heater.
The ignition switch does not "ground" through anything. It switches the power supply only. The starter, starter relay and coil all ground locally to themselves.

We need a better explanation of what is going on.

Is everything stock or has there been any obvious messing around by a PO with the wiring? What year truck?
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  #7  
Old March 9th, 2016, 11:55 AM
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It cranks but will not fire unless the heater switch is above the off position. It is the standard variable speed heater control - controlled by the lever next to the binnacle on a ROW 1986.

One detail I had not thought of before: my son messed around with the radio wiring last fall - he knows even less about wiring than I do. The radio still does not work so I assumed he didn't screw anything up and never looked at what he did. The heater motor has likely been on every time we have driven since then - until today. Based on the comments above, if he loosened a ground wire somewhere then this could be the result?
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  #8  
Old March 9th, 2016, 12:03 PM
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Really baffling. The heater motor gets switched power via its own fuse and the speed lever switches the ground side of the motor. There should be no interaction with anything else in the wiring.

I would start by pulling the binnacle and looking over the wires that go to the heater switch and looking for problems or PO modifications. Beyond that, you need to grab a meter, a schematic and start tracing faults. If you don't like electrical things, you need to learn fast or find someone that does.
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Old March 9th, 2016, 12:07 PM
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It would be pretty amusing if the PO took the +12V for the ignition from the heater/blower control
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  #10  
Old March 9th, 2016, 12:12 PM
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Quote:
Originally Posted by sonoronos View Post
It would be pretty amusing if the PO took the +12V for the ignition from the heater/blower control
That does not explain it though as it is ground switched.
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  #11  
Old March 9th, 2016, 12:17 PM
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If you turn the heater off while the car is running, does it stall or stay running?
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  #12  
Old March 9th, 2016, 12:24 PM
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Uncle and good luck. Monopolization is never a good thing.
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  #13  
Old March 9th, 2016, 12:38 PM
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Well at least my Black Magic theory is still in play.
I have not tried to turn the heater off when the truck is running, I will try that tonight.
I will also take a look behind the binnacle and at the fuse box this weekend to look for anomalies - starting with ground wires.
No one has touched the ignition wires and the ignition & starter work fine regardless of the heater position. The engine just won't fire unless the heater is on. Maybe Nomar got it right with the heater fan doubling as a bellows.

------ Follow up post added March 9th, 2016 12:46 PM ------

BTW ... thanks to everyone for the comments and ideas. At least I have a place to start.
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  #14  
Old March 9th, 2016, 01:22 PM
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attached is a wiring diagram of how it should be wired
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  #15  
Old March 9th, 2016, 02:04 PM
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Interesting diagram.
Reading it the switch sends the (-) current to the blower motor.
There are 2 paths one for half speed that has a resistor and one for full speed.
The (+) side of the blower motor gets power through the IGSW and Fuse Box.
This is the same way the late Series III's are hooked up, but for some reason some jackass decided to put an inline fuse in the White with Orange circuit instead of passing it through the fuse box (probably because the Series III fuse box is smaller than the 110).

So I think the real question here is how can a switch that sends (-) power to a blower motor (which is what the diagram shows) interrupt the (+) power going to the coil.
Furthermore, the engine is grounded because it spins over.

Andy, let's try an experiment.
I want you to take a set of jumper cables and attach one to the (-) side of the battery and attach the other side to the coil body (not any of the coil wires) and then turn off the blower and see if the engine starts.
If it does start this way, as weird as it sounds, the ground for the coil at the bulkhead is being drawn through the base of the blower motor.
And the (+) is not being interrupted to the coil.
Andy please verify this with a test light to the (+) side of the coil with the key on the run position, but the blower switched off.
Please ground the test light to the (-) battery and not have the jumper cable to the coil from the (-) battery when you run this test.

My guess is with the blower switched off the engine will shut down without the (-) jumper cable mentioned above.

If this is as I describe the problem is the bulkhead is not properly grounded.
If it is not, I have no idea what is wrong.
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  #16  
Old March 9th, 2016, 02:15 PM
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My heater blower motor would run whether the car was switched on or not, I replaced the fuse and it was fine. I would start with replacing the fuse for the blower motor and for the ignition.
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  #17  
Old March 9th, 2016, 02:16 PM
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Great, thank you. I will try the jumper cables and also replace the fuses. Hopefully I can get to it tonight and will report back. I won't be home Thursday or Friday so if I can't get to it tonight I may not report back until this weekend.
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  #18  
Old April 2nd, 2016, 02:29 PM
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and the verdict is ????
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