You may have an issue within the
harness itself.
The Excel cart has
453Ω resistors in each of the throttle wires.
You can disconnect the 16-pin Connector from the Controller and the 3-pin connector from the MCOR and measure those resistors.
Controller Pin #1 to MCOR - White wire
Controller Pin #2 to MCOR - Yellow wire
Controller Pin #3 to MCOR - Purple/White wire
You should measure approximately 450Ω between each of those connections above.