M1008 no start! Starter relay?

[TVOLLMER]

I have a M1008 that has never had electrical starting issues. I went to start it last night and it would not turn over, no clicks at all. All the dash lights and glow plug wait light worked like normal. battery gauge shows a good charge. I confirmed the battery charge with a meter and battery tester. I then tried to turn it over again and got smoke from under the hood. It was dark so had trouble finding the smoking wire at first. there is a two-post junction to the left of the glow plug silonoid with an orange wire that appears to go into the main wire harness. The wire burned the insulation off about an inch below the connection.
Could this be the starter relay issue everyone says should be changed? Any help would be great.

 

[85CUCVtom]

Is the wire that burnt up a fusible link? If so, you burnt it up. Repair that first then I would load test my batteries then check my connections and make sure everything is tight and not overly corroded.

The relay that everyone talks about is under the dash. Most people do the Doghead mod. Look in the stickies on the top of the CUCV forum for more info.

 

[TVOLLMER]

Ok. I am not sure if what burned up is a fusible link. How do know? I guess i got lucky with this truck as far as the electrical goes. untill know. Will the tm's go over this? i have been over the from top to bottom, and have YET to find any corroded wires or connections but i will go over everything again and check out the tm's.

 

[MarcusOReallyus]

Yes, the TMs cover it. The starter relay is known to be a problem, and the doghead relay mod cures it. Check the stickies at the top of the CUCV forum - it's on there.

A fusible link will look like a short section of wire that is much bigger than the wire it's part of. If it's burned, it may or may NOT show on the outside. Do a continuity check on the wire. Make sure your batteries are disconnected when doing any continuity test.

The sticky section also has a thread on "Fusible Links 101". Recommended reading!

 

[TVOLLMER]

I guess what my questions should have been what could go out or change in a matter of 12 hours to cause this. My brother started the truck 12 hours before me and it started right up, he moved it 50 ft and parked it. according to the wiring diagram the wire the burned up is a fusable link wire that is connected to the left post of the engine wire harness block.

 

[Terracoma]

A fusible link will look like a short section of wire that is much bigger than the wire it's part of.

This is backwards... Fusible links are always physically smaller than the wire they protect.

... there is a two-post junction to the left of the glow plug silonoid with an orange wire that appears to go into the main wire harness. The wire burned the insulation off about an inch below the connection. Could this be the starter relay issue everyone says should be changed?

I guess what my questions should have been what could go out or change in a matter of 12 hours to cause this ...according to the wiring diagram the wire the burned up is a fusable link wire that is connected to the left post of the engine wire harness block.

This orange wire you speak of is not part of the starting circuit, as you found in the -20TM.

Rather, the orange wire is a fusible link (20-gauge), part of the charging circuit, and it sounds like it cooked itself protecting the red primary wire (16-gauge) connected to it. This red wire runs through the corrugated split loom below the glow plug relay to the driver-side alternator's plastic plug.

Keep in mind that most of this wiring is 25-years-old, and what was fine and functional yesterday might be very unhappy today. I once had a fusible link that looked good when casually inspected, but was completely corroded inside and was intermittently passing current depending on how it was wiggled/oriented. The vibration through the chassis was enough to make it act up, and more than once the truck would shut off with no warning, while driving down the road.

 

[byrnestree]

i have a siilar problem with my truck. new starter, alternators, good batteries, new fusible links. i put a new relay in adn nothing...no crank i just hear clicking. i went thru all of the wiring and checked for shorts and corrosion. is it possible i boguht a bad relay? would the doghead relay mod fix this problem?

 

[MarcusOReallyus]

This is backwards... Fusible links are always physically smaller than the wire they protect.

The wire inside is. The casing makes it look bigger.

 

[85CUCVtom]

So what the status on your truck? opcorn:

 

[TVOLLMER]

I am still not sure what is going on. I need to find a better wiring diagram. The diagram I found shows the wire that burned is part of the headlight circuit, doesnt make sense so I am sure I have the wrong diagram because the headlights work and wire doesnt smoke when the lights are on. By the time I get to the truck it is dark so it makes it hard to see what is going on. I should be able to get out there tomorrow before dark. I will post what I find.

 

[Terracoma]

The diagram you want is Appendix F, Figure 9, "Charging Circuits (All Except M1010)".

Wire size chart to decrypt the diagram is located in Chapter 2, Page 27.

 

[TVOLLMER]

Thanks. I found the correct diagram after my last post. I am headed out tonight to try and find the issue. But i didnt know about the size chart. I will post what I find.

 

[TVOLLMER]

I went out to look at the truck last night. The wire that burned was part of the ignition circuit. I simply replaced the wire that burned from a m1009 wire harness that I thankfully kept, and the truck started right up. Nothing about the wire looks bad. Not covinced the problem is fixed. But hoping it was just that one wire that shorted. Time will Tell.

 

[TVOLLMER]

I know it sounds crazy to replace a 25 year old wire with another 25 year old wire. I did this for testing purposes. I wanted the fusable link in the wire just in case something went wrong.

 

[MarcusOReallyus]

Fusible links often show no sign of being bad, even when they are completely fried.

 

[TVOLLMER]

I drove the truck last night delivering two cords of fire wood, got to the customers home and the gremlin appeared again. Electrical problems have a funny way of showing up in the dark and this one did. Along the back of the intake manifold there is a two wire connector that has a resistor jumping the connector with a bunch of tape holding it in. Over time I guess it rubbed through and shorted on the intake manifold. I taped up the connector, fixed the wire again, and the truck fired right up.

The fusible link should have fried before the main wire. Right? Isn't that what its for?
Any thoughts?

 

[Warthog]

That "resistor" is actually a diode. It is in the Water in Fuel circuit of the fuel filter.

Diagram E-1 from the -34 TM

 

[TVOLLMER]

Ok. Thanks for the info.