Fuel guage

I have a 83' chaparral 187 with a mercruiser 470.. Everything works on the boat but the fuel guage, i know its electric, checked all fuses and still doesn't work. Tank is under the floor. Any ideas?

there should be tank access to the fuel hoses and sender plate., If the floor has been replaced you`ll have to cut some holes in the floor for access.
pink wire goes to the center stud, black wire to tank ground plate or to a mounting screw..grounding the pink wire should make the gauge go full scale.If not supply a ground from the - battery and retest.
If gauge does not move ,place ground jumper from the battery to the pink wire at the gauge. gauge should go full scale. These test need 12v at the gauge so make sure you have that first.