My dash lights and tail lights quit working, and fuses are good but cant find the fuse box under the hood anyway its a 1988 gmc sierra 1500 series

Might be your power distribution center under the hood. I have ran into issues where bad connections caused excessive heat around the fuse and relay contacts and actually melted spots in the box. Remove the back cover and look for melted or discolored spots.

check power door lock relay under hood fuse block

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its on the transmission back -up light switch do you have trailer lights check and see if the pig tail on the 4 way is going to ground i seen this blow fuse after fuse

When dash lights don't work odds are the tail lights don't work either.Sounds like Dimmer switch may be a problem.

check all fuses again under hood and under dash if all are ok suggest you replace headlight switch ;also
check dimmer switch for dash

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most like u have a blown fuse most of the time in cars they connect the tail light and instrament lights to 1 fuse

your fuse panel is either under the dash by the drivers left knee or on the side of the dash where it meets the door. the radio fuse should be the second from the top right side of the fuse panel. its a 10 amp fuse. the power for the switch should be a 16 gauge wire run from the passenger firewall (under hood.) behind a plastic cover where a lot of wires are bolted to posts. that red wire feeds power to almost everything in the cab. it runs behind the glove box and has a disconnect there. if the fuse is not bad and the wire looks good, check the ground on the passenger door "open switch" (the one that is supposed to turn on the dome light. that is where the whole system is grounded for the int. lights lights

The horn fuse is in the under hood fuse box. It is a 20 amp fuse. Good Luck

I assime you are a mechanic so; use a test light and, check for a missing ground