my homemade 4x4

[conoverbandit]

Hello,
I have a question, I got a 75 chevy short box that has been converted to 4x4 using 77 chevy chassis (done by me) the question is when i got this truck my neghibor had put a dash in it with a tach. unsure of what year but i can't get it or the speedo to work. I have changed the speedo cable with one i know works but it still won't. Hardly anything works in the dash it's self i think cause the guy just put the dash in with out the harness with it, he told me it had "idiot" lights and he wanted a tach. what can i do to get the dash working properly? only thing that works is gas- (i think i haven't ran out yet by using it) and the oil gauge ( it has a line that hooks to it) but the amp gauge shows "dis charge" all the time, i upgraded it with one off a conversion van (120 amp) and know it's good,keeps batt. up to, but the gauge still shows "discharge" any help would be aprechieated. Thanks