Short in my dash ?

Hello, I have an 85' blazer with an 88 4.3 engine in it, I'm having this problem where at night when i have my lights on, My dash lights will just go hay wire, If i tap my dash kinda hard they'll go back to normal, I'm assuming this is probably a short, but dont wanna go pulling it apart if its something else,
And also my fuel gauge isn't working right, It'll bounce around, Sometimes it'll drop all the way down below " E " , Sometimes when i shut if off it'll move to about a quarter of a tank, then when i turn it on it'll drop down to " E " , No idea what it is, Just looking to see if anyone could help me, Thanks.

most likly is gauges wire plug is not all the way in
reach the plug and push it in

Do i need to take the front of the dash off to get to the " wire plug" ? or do i have to go from underneath the dash ?

you go from underneath

Your gas gauge is probably a bad sending unit-try twisting the dashlite dimmer switch and see what happens-prob. a bad connection in the switch-beating on the dash shakes it around enough to make a connection

I figured it out, My light switch had a loose ground, My gas gauge is still wrong, When I fill the tank, On the gas gauge it says just alittle over 1/4 of the tank, And it'll drop way down past " E " , So i'm guessing its the sending unit in the tank , Thank you all for your info on the whole dash thing, Kinda feel dumb now heh, Any info on the whole gas gauge/tank/sending unit would be cool, Thanks again :) .