Fuel guage help!!!!!

[Rtrucking40]

So ive never had a working fuel guage in my boat since ive bought it and decided to fix that this year. I bought a brand new gauge and sending unit. I did a dry run before installing everything and with all the wires hooked up the gauge read perfect when i moved the float on the sending unit. So i had the boat in the water for the 1st time yesterday and as soon as i fired up the engine the fuel gauge was bouncing all over. Heres how i have my wiring ran sending unit wire to sending unit post on gauge, ground from sending unit direct to battery. Ignition hot switch to gauge for power when keys on and guage grounded in line with all other guages. Any ideas what could be acting up?!?

Edited April 8, 2018 by Rtrucking40

[Sean Youngblood]

I would guess the ground wire from the sending unit should be grounded to the ground on your gauge.Here is a link with good info  .https://www.sailmagazine.com/diy/test-replace-fuel-gauge-sending-unit

[Rtrucking40]

Ty for the reply i had it like that and it just peged the guage to full when the sender ground went straight to guage 

[gasman2438]

the ground on the gauge is only for the light. the important one is the ground to the sending unit.

[Xxx]

The sending unit is like rheostat that feeds ground to the guage not + juice that’s recipe for disaster.  

[garrymny]

As I recall, my sending unit is grounded right at the aluminum fuel tank. The other wire goes up to the gauge.