Hi Stuart
Had the switch out a few times.
The tail lights are fine, been through all the bad ground problems. When the brake lights are switched on, they come up fine, equally bright either side; but I can't get the two brake lights to work together, that's the basic problem.
Front turn signals are indeed bright, and flash correctly even with parking lights on.
I agree that the info on the GMC site does seem a bit ambivalent; that's why I'm checking on here to see if anyone else has had the same problem. Trouble is, as you'll know, original GMC's of that era are rare even in the USA; there are to my knowledge less than six in the UK, and mine's the only 63!
