[JohnnieB]

Town, it sounds like you have at least two problems.
1. A bad connection in the throttle circuit.
2. Very sick batteries.

The throttle box does two things:
A microswitch in it closes the solenoid. That part is working if the solenoid is clicking.
The ITS coil and plunger tells the controller how much current to pass. That is the part that doesn't seem to be working all the time.

Like Bowslayer said, jack it up and wiggle the wires. (Hint: the Black and White wires are the ones that connect the ITS to the controller)


Like rib33024 said, approximate voltages don't tell us much when mere fractions of a volt have significant meaning.

On the other hand, the approximations you gave, do paint a very dismal picture of your batteries.

A fully charged 225AH 6V battery (6.37V) in useable condition, will produce 100A for well over an hour before it drops to 5.25V.
You state your batteries went from "a bit above 6VDC" down to "about 5 VDC and stayed there" in 15 seconds.
If that information is anywhere near factual, your batteries are well beyond their usable life.