I had a complicated problem with my M1008 a while back that I'm just now getting around to looking into. Haven't had any luck in the TM's or Forum.
Background: the starter relay has been removed and a push-button switch installed in its place, this has worked flawlessly for 2+ years. The GP relay resistor bank has been removed and rerouted 12v power to the GP Relay to the front battery with a stock wire w/ fusible link. This has also worked flawlessly for years. Also, and I'm sure this is pure coincidence, but still worth mentioning, that previous night was the first time that I had used a new magnetic engine block heater on the oil pan. I used an appropriately-sized, grounded extension cord to a 20-amp, grounded outlet in the garage. Other than this, nothing had changed and the truck had been working great as a daily driver for a long time.
The symptoms: Cold winter day (I said it has been a while), turned key forward, GP Relay clicks, Volt meter drops accordingly, WAIT light goes on, then off, depress accelerator pedal, push starter button. Motor cranked for about 20 seconds without firing, released the starter button, starter motor kept cranking! Turned key to "OFF" and removed key, still cranking. Frantically reached under dash and removed the leads to the starter button, still cranking! Popped the hood, ran to the saddle box, grabbed the tools. By the time I was able to disconnect the battery leads, the starter motor was smoking. I first disconnected the "+" from the front battery, then the "-". The starter motor stopped cranking, but then some of the wires along the upper part of the firewall near the distribution block next to the GP Relay began to melt and smoke. There was also smoke coming from the Driver's side Alternator. Fusible links popped and a small fire started along the firewall! I grabbed the fire extinguisher from the cab and put out the flames and disconnected the rear battery. Stood there in shock for 20 seconds to let the adrenaline die down and contemplate what had just happened. I had to get to work, so I closed the hood and went on with life. Massively cold and brutal winter kept me from looking into it until spring. I've had few chances to look into it since, but need to get this figured out and wrapped up now.
Progress: So far I have replaced the burnt wires and fusible links along the firewall, tested for continuity every wire I can find running along the firewall, to and from both batteries and alternators, checked resistance and continuity on all grounds, tested the proper function of the starter switch, and found a loose fuse in the fuse block, that when wiggled would make the Voltmeter in the dash come on or off. This is really strange because it is the #7. 30 amp Unmarked (Headlight) Fuse in the Unit Maintenance TM. I don't see how the Headlight fuse has anything to do with the Voltmeter when there is a separate fuse (#12) for the Voltmeter. I have also checked that all of the wires are properly connected and tight at the starter motor. Also, when everything is connected up and powered, if I turn the key forward to "run" and hit the starter button while the #7 fuse is "connected", the starter will crank (and not stop) and the fuse next to the GP Relay running to the driver's side alternator will blow and I have to disconnect both batteries fully. However, if I turn the key to "run", then wiggle the loose fuse (again, #7, supposed to be for "Headlights", the voltmeter and gauges in the dash die and there is no power to the starter, won't crank. Really strange. I don't see how they are connected.
My thoughts: 1: Problem with the starter motor solenoid, that might explain why the starter kept cranking, but I don't understand how that would make the wires on the firewall burn or cause the alternator to smoke.
2: Something, somewhere is shorted to ground, causing current to still flow through the wires on the firewall and back to the alternator when the
front battery was disconnected.
3: There is something wrong in the fuse panel, shorted, bad connection, connected incorrectly (previous owner), etc.
4: Multiple, unrelated issues at once?
I could really use some help here. I'm reaching the end of my troubleshooting abilities. I plan to bring in the starter to have it checked out, but again I don't see how a bad starter solenoid could cause all of these other issues. Any wisdom and experience would be greatly appreciated.
Background: the starter relay has been removed and a push-button switch installed in its place, this has worked flawlessly for 2+ years. The GP relay resistor bank has been removed and rerouted 12v power to the GP Relay to the front battery with a stock wire w/ fusible link. This has also worked flawlessly for years. Also, and I'm sure this is pure coincidence, but still worth mentioning, that previous night was the first time that I had used a new magnetic engine block heater on the oil pan. I used an appropriately-sized, grounded extension cord to a 20-amp, grounded outlet in the garage. Other than this, nothing had changed and the truck had been working great as a daily driver for a long time.
The symptoms: Cold winter day (I said it has been a while), turned key forward, GP Relay clicks, Volt meter drops accordingly, WAIT light goes on, then off, depress accelerator pedal, push starter button. Motor cranked for about 20 seconds without firing, released the starter button, starter motor kept cranking! Turned key to "OFF" and removed key, still cranking. Frantically reached under dash and removed the leads to the starter button, still cranking! Popped the hood, ran to the saddle box, grabbed the tools. By the time I was able to disconnect the battery leads, the starter motor was smoking. I first disconnected the "+" from the front battery, then the "-". The starter motor stopped cranking, but then some of the wires along the upper part of the firewall near the distribution block next to the GP Relay began to melt and smoke. There was also smoke coming from the Driver's side Alternator. Fusible links popped and a small fire started along the firewall! I grabbed the fire extinguisher from the cab and put out the flames and disconnected the rear battery. Stood there in shock for 20 seconds to let the adrenaline die down and contemplate what had just happened. I had to get to work, so I closed the hood and went on with life. Massively cold and brutal winter kept me from looking into it until spring. I've had few chances to look into it since, but need to get this figured out and wrapped up now.
Progress: So far I have replaced the burnt wires and fusible links along the firewall, tested for continuity every wire I can find running along the firewall, to and from both batteries and alternators, checked resistance and continuity on all grounds, tested the proper function of the starter switch, and found a loose fuse in the fuse block, that when wiggled would make the Voltmeter in the dash come on or off. This is really strange because it is the #7. 30 amp Unmarked (Headlight) Fuse in the Unit Maintenance TM. I don't see how the Headlight fuse has anything to do with the Voltmeter when there is a separate fuse (#12) for the Voltmeter. I have also checked that all of the wires are properly connected and tight at the starter motor. Also, when everything is connected up and powered, if I turn the key forward to "run" and hit the starter button while the #7 fuse is "connected", the starter will crank (and not stop) and the fuse next to the GP Relay running to the driver's side alternator will blow and I have to disconnect both batteries fully. However, if I turn the key to "run", then wiggle the loose fuse (again, #7, supposed to be for "Headlights", the voltmeter and gauges in the dash die and there is no power to the starter, won't crank. Really strange. I don't see how they are connected.
My thoughts: 1: Problem with the starter motor solenoid, that might explain why the starter kept cranking, but I don't understand how that would make the wires on the firewall burn or cause the alternator to smoke.
2: Something, somewhere is shorted to ground, causing current to still flow through the wires on the firewall and back to the alternator when the
front battery was disconnected.
3: There is something wrong in the fuse panel, shorted, bad connection, connected incorrectly (previous owner), etc.
4: Multiple, unrelated issues at once?
I could really use some help here. I'm reaching the end of my troubleshooting abilities. I plan to bring in the starter to have it checked out, but again I don't see how a bad starter solenoid could cause all of these other issues. Any wisdom and experience would be greatly appreciated.
