The first thing you will want to check is the hardware used to install the trailer hitch on your 1998 Mitsubishi Montero Sport. If the hardware is not properly torqued down to the specifications indicated in the instructions (linked to the right for reference) then that could be the issue.
The hardware has to be torqued to the specifications. Too loose and the hitch can come off. Too tight and it can damage the hitch and vehicle frame.
If the hardware is torqued properly then you might... view full answer...
What you described sounds like your Primus IQ part # TK90160 isn't mounted level and because of that is behaving erratically at low speeds. I attached a picture that shows how it has to be mounted.
The wire you used for the red wire of the brake controller appears to be the correct one based on what you described. view full answer...