[AT] tractor electrical question

[John Hall]

Got what I hope is a simple question. On my IH 454 tractor, is the 
voltage going to the coil a constant 12V? I'm having some issues with it 
running bad when it gets hot (I've already replaced everything but the 
plug wires). Found out today that if I run a jumper wire from battery to 
the coil, the problem goes away. Take it off problem comes back, put it 
back it goes away, take it off, it comes back. So I am tracing the 
wiring but this one isn't simple, new enough there are tons of gauges, 
fuel solenoids, safety switches, etc. Anyway, if I check voltage at the 
coil, the fuel solenoid, and there is one small terminal on starter 
solenoid that all read 12V if the switch is on. If I bump the engine 
over slightly (I guess the pts are closing) then the coil and starter 
drop to just under 6V, fuel solenoid stays the same. So shouldn't there 
always be 12V at the coil?

John Hall