I managed to spend some time today with the meter on the dim and dip (low and high) beam circuits on the MR2. Remember mine is a facelift model so already head separate bulbs with separate +ve and -ve for each beam. Nostromo I think you might have an easier time here if yours is a pre-facelift as they should have had a single H4 type connector for the original MR2 lights if I recall.
IGNORE FROM HERE ON AND READ THE NEXT POST BELOW ... AS ALWAYS SIMPLER IS BETTER !!!
Anyway, the issue is that for the facelift MR2 you need to somehow switch the -ve connection depending on whether you have dim or dip setting on the stalk (or you are flashing dip). After looking online I believe the way to do this is with a changeover relay that in normal state (unenergised) has the dim (low) beam -ve but when it is energised (with the dip/high beam circuit) it switches to the dip (high) beam -ve.
Not sure I’ve got this 100% correct and I have a couple of changeover relays in the post to me tonight, but I having managed to test this manually by changing the connections on the fly and testing it seems to work, so long as I’ve got my theory right on how the changeover relay works. Now the challenge here and going back to what Retro200 said, the changeover relay is 5 pin not 4 pin so this may all be way wrong.
Here’s a picture (apologies for how poor this looks but it was just a quick sketch on the iPad) showing how this should work in practice ....
I will come back to you all once the relays have arrived.
Er... just looked again at wiring diagram, and I think this will work but when on main beam the low/dim circuit will be active as well. I’ve checked and I don’t think this is a MOT failure although won’t be great for heat in the bulb/lamp housing and will probably burn the bulb out quickly. To over come this a second changeover relay would be needed I believe to switch off the dim/low power when the high power circuit is on.