Code 28 is motor temp hot cutback. That sounds more like a bad connection to the temp sensor.
Glad you got it working. Yes, you either need interlock connected to controller 12V or set it to type 2 (interlock turns on with KSI). Make sure it's controller 12V (pin 25) and not your system 12V (they need to be isolated).
You can turn interlock and KSI on/off in any sequence.
There's a setting called high pedal disable (HPD) that checks throttle <25% before interlock is enabled, or it throws code 47 and cuts power. It might be enabled for golf car programming, but I'm pretty sure it's turned off for their standard auto/motorcycle program. Either way, if throttle is 0 when you turn on it won't fault.