Truck won't even grunt with new batteries

Sounds like its time to start chasing the power wire going to the starter solenoid.

 

Get a test light and start working your way down from the batteries to the switch to the relay to the starter .

you got a dirty connection somewhere that needs taken apart and cleaned

but be careful .
Shorting out that kind of amperage can cause a problem

I’ve done plenty of trailside welding repairs on jeeps using two batteries , a set of jumper cables and a coat hanger .
Two normal car batteries is enough juice to weld a broken tie rod back together

On a tractor you have the equivalent of four to six car batteries .

 

Now thats some Maguire'n

 

Clean the cables. Check the grounds. If it ran when parked it's usually something simple.

 

did mice chew through important wires?

 

Yep

Appalachian Engineering
I grew up 6 miles from
The nearest paved road .

they filmed a lot of scenes from Deliverance , about two miles from our house .
My older brother went to school with the banjo boy .

But Don’t call us hillbilly’s anymore .
The correct term is Appalachian American.

800 to 1000 amps at 12 volts will weld pretty good .

when the starter solenoid shorted out on my Ford LTL 9000 , it got white hot , enough to melt the fuel line about 18 inches above it ,
And diesel dripping onto white hot metal
Is a fire that no fire extinguisher can put out .
I used both of mine , and the one from the nearby Waffle House and the one from
The responding police car .

Only thing that saved the rig was when the FD showed up and had a cable cutter on a stick to chop the battery cables .

 

Clutch pedal sensor bad?

 

379's dont have a clutch pedal sensor.. not sure what a clutch pedal sensor ever is or what it does .. in fact never heard of a clutch pedal sensor

 

Except for the Jake switch.