Hi there! I javelin tried all of these steps and am unable to locate the issue. Multiple replacements of all 3 boards, motor swaps, harness swaps, leads multimetered. No luck. Any help?

You need to check the resistance of the motor field, should be approximately 0.7 ohms or failing to disassemble the engine and check the resistance of each field, you'll have to cut them, the resistance should be aprox 2.2 ohms, to my I cause me many problems when from the beginning was the motor.

code 18 - Right motor, faulty field drive

Possible causes:
- faulty right motor field circuit
- faulty H Bridge board
- faulty logic card
- faulty controller harness

This code is triggered when the logic detects over current for right FET

Checks
- disconnect battery plug
- check right motor field cable terminals, logic card CN2-13 terminal and H-Bridge board CN2-16 terminal for abnormality.
If unacceptable: correct or replace cables
If acceptable:
check continuity between following terminals - right motor field cables, and also check logic card CN2-13 and CN2-63 (Neg)
If shorted: correct or replace faulty circuit
If not shorted:
turn on key and confirm code 18 is displayed
confirm voltage between CN2-13 and CN2-63 (Neg) with multimeter
If about 15v replace logic card
if about 0v replace H-Bridge board.

hope this helps