i'm having some trouble wiring up my 1990 740 wagon with a trailer harness - being in north america i have to go from a 5 wire setup (with amber flashers) to a 4 wire setup to mate up with the trailer - the trailer has completely new wiring, good ground and lights up like a christmas tree on another vehicle but sadly not on mine

i am currently running a draw-tite brand adapter/wiring harness but i have noticed that the voltage on the trailer side of that harness is only between 9-10V and slightly less at the trailer lights when hooked up (normal loss through long run of wiring) - my thought is that this low voltage is giving me the problem of dim lights - i have tested the ground on the car (same as powered antenna) and this seems find as well

i have read other posts that mention using a powered tail light converter but as this runs in the neighbourhood of $50 canadian i am a little reluctant to buy one if it will not fix the problem - someone has also mentioned trying to go with 6V bulbs on the trailer but i have a feeling these will be hard to find - any suggestions???