Gregsend54 wrote:Trouble is I don't know the rest of the circuit.
Herein lies the problem. I suspect that they've just tapped in to the high beam somewhere behind the headlight then run that through a switch and back to a relay which switches the power for the lights. Poor practice since it uses double the amount of cable that is necessary.
I think I know what's been done, but would need to see it and check both what's there and how your new switch operates, with a multimeter. Without such it's a bit hard to tell you what to do, since there's the chance I could be wrong.
Gregsend54 wrote:For a supposed factory fit it's a nightmare under the bonnet. Some plugs into factory loom some joins onto wires taped up with electrical tape.
Definitely not "factory", or even professional. If it was my car I'd rip it out and start again. Depends on whether you feel comfortable designing and making a new loom. If you don't then I'd be looking at purchasing the harness that Perception Lighting offer. That's pretty much "plug'n'play". Maybe you could get them to take back the switch that you bought separately.
Mitsubishi use two, sometimes three, different circuits for things like headlight switching. First there is a circuit that just sends a signal between the switch and a control module (usually the BCM). The BCM is a computer that interprets the signal and then activates a relay to switch the headlight power which is the third circuit. Circuit diagrams are in the online manual (see Forum Directory). Designing a harness to work properly with such a setup can be a bit challenging, depending on what you're doing.
The correct way is to tap in to the line between the BCM and the original relay (can be difficult to locate) or tap in to the factory relay output and use that tap to activate a relay which draws power direct from the battery and feeds the lights. I'm not sure if the Perception harness does this or is a bit of a hybrid design - can't tell just from a picture on their website.