Pull the bulbs out, get a test lite on the contacts in the socket to find the 12v contact, then put the gd side of the test lite to the socket housing, if the gd is good it should lite, do this on all the suspect lites.
Being a Camaro lover,I just have to,wasted post I know,but I had to.I don't know whats wrong with a Vette's tail light,I've never seen them!With that said,Max is right on the money,it's a ground issue.
__________________ If it ain't broke.......screw with it till it is.
Even at a Mensa convention,
Someone's the dumbest person in the room.
If the ground on one light isn't proper, the power will flow through other lights to ground in ways the system wasn't designed for, hence the weirdness.
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1988 9C1 - Modified LM1 @ 275HP/350TQ - TH700R4 - 3.08 8.5" Disc Rear - see it at http://www.silicon212.org/9c1!