I have dual tanks. I have a toggle switch on the dash to switch tanks. When the tanks are full the gauge reads 1/2 full on both. Usually that means a bad ground. I looked at the sending unit on one tank and they ran the ground to one of the 4 bolts that hold down the gas fill lid. I dont see that being a good ground. Do I run it to the block or to the terminal block? Where does your grounds run to from the sending unit? Thanks for your help.

I'm having gauge issues too, grab an ohm meter and check the sending unit. It should read like 240 ohms empty and 33 full, for most gauges.

Ok i will go out and trace my wires 

the wire in the center of the sender is for the gauge.  The ground is wired from the ground terminal or block to one of the 5 sender attaching screws.  The wire that goes from the sender attaching screws to the fill neck is the ground for the filler neck.  Check the ground connection for good contact.

p-jet

I'm not sure if its right or necessary but here's how it was done on my Daytona.  I just put the tanks back in so I snapped a couple shots for you.

 There are grounds on the filler caps, the senders and the tanks themselves.  Not sure why it has them on the tank bodies but it does. 

I understand, but I thougt that was common knowledge

must be if i know it

 

Do you suppose that filler neck ground is to eliminate the chance of a spark while refueling? I dunno, just asking.

I was thinking the same thing. It makes sense to me to have the tank/sender and the filler neck grounded, Wouldnt want to creat sparks when shoving the gas nozzle in...

Thanks for the pictures. Thats how mine looks too. Where does your ground run to that comes off the tanks? I'm also guessing that the ground that runs to the filler neck is for static. Mine tells me when its empty too. I found that out this weekend. It just shut down, Switched tanks and was off again. I think I need to make a good ground from the block or battery and run everything to that. Thats a good idea with the test light. Clamp the clip to a power source and touch the sending unit grounds and see if the light comes on. I will try that.

I have  a problem suspecting two bad grounds which is what you're showing.  How did they wire up the switch to indicate the different tanks on the gauge?  If they have the senders paralleled you're cutting your resistance in half.   They must stay seperate.

Just a thought.

Yeah I'm going to X2 this idea as a possible reason both gages only read to 1/2 when they are full. Not likely that both senders are bad. Or, the gage is the problem kid and it has a poor ground or something. So I'm voting for a check of the quality of connections and type of switch you have and the wiring between it and the gage.