I have no dash lights on my 86 chevy c10 need to know which wire on plug to cluster is for dash lights so can check for power

First check that you don't have a tail light out, they did this so that if a rear tail light was out the dash board lights would not come on. Next if both rear running lights are ok then the most common problem for this rig was the light switch, it is not to difficult ot replace. Also there was a problem with the connetors on this truck they would heat up and come loose. so pull out the light switch knob and reach under the dash and push the spring loaded button on top of the light switch to pulll out the knob, next unscrew the beuty ring with a screwdriver and pull down the swtich and the harness, I belive the number 7 pin was the one that would burn out.

It is the "GRAY" wire at the cluster plug. There is a 5 amp fuse in the fuse box that feeds the lights. The fuse is marked as "INST" in the fuse box.
Good luck.

If there is no power at the 5 amp fuse, then where do you go?