Needles in gauges just peg out

Well when I got my car it came with a extra gauge cluster because the one that was in was broken. The speedo was broken.
So yesterday me and a friend swapped out the gauge clusters and now the Temp gauge and Gasoline gauges just move across the whole gauge (pegging out).
My friend is telling me there is probably a electrical problem some where.
For now we unplugged the sending unit for the Temp gauge and Gasoline gauge so they actual gauge does not get messed up by pegging out every time the car turns one.
The needles move just fine across too if that makes a difference (very smoothly).

Any ideas why the needles keep pegging out?

Thanks alot!