We do offer two universal-fit 4-pole wiring harnesses for your 1999 Mitsubishi Montero but neither is a plug-and-play type. Both can be seen on the link provided, part # C56175 from Curt and part # 119178KIT from TowReady, and both will require you to splice into a few wires at the Montero's tail light assemblies.
If your Montero has LED lights you will want to use the TowReady harness # 119178KIT but if it uses incandescent lighting you can use either the TowReady or the Curt # C56175.... view full answer...