crazy gauges

ok heres a run down.

coolant gauge - works fine

fuel gauge - works fine till it gets to 1/2 tank them bottoms out and ocasionally works when below 1/2 tank.

speedo works fine


amp gauge - worked fine till i had the intake off, now shows discharge all the time. (alternator is good and charging the system)


oil light - not hooked up but comes on every so often.



any ideas appreciated.