Andy
Since I don't know what modification you made to move the dimmer switch from the floor up to the combi stalk on the column, there realy isn't much I can point to as a possible problem, other than saying from my experience, first you should undo the modification and see if it works as original. Most of the time it will.
The high beam switch on the stalk controll is a momentary contact and would need some sort of latching relay to hold on the high beams, I have seen SL's that used a relay from a VW Rabbit (yes it was a long time ago) to use the flash to pass switch as the hi/lo beam controll.
It doesn't seem likely to be a fuse problem, because the low beams have seperate fuses for the left and right.
Al
