i recently installed a new sending unit in my aftermarket gas tank. its mounted between the rails. anyways, the gauge reads fine (1/2 full) when the key is in the"on" position. but when i crank the engine and it fires, the gauge drops to empty. any ideas would be appreciated thank you

 

Has this setup been known to work properly before or is this an all new setup? If it is an all new set, where are you getting the power from for the fuel gage? Sounds like the source is loosing voltage after the truck starts. Maybe try a different voltae source? Are all the gages powered by the same source? Do all the gages quit working?

 

I agree, sounds like dropped voltage at ignition...but, if you did nothing but plug in the new sending unit??? Make sure the connections at sending unit are correct and is your truck 6 or 12 volt? and same question for the sending unit? If they dont match this could cause some funny business.

Ed

 

the power is coming from the fuse box and the rest of the gauges work fine.i'll check the voltage when i start it again. i ran new wires because the old unit was toast. so i thought with a new gauge i would run new wires. its only 2 wires so it shouldnt be that hard to figure out. could it be the battery is not holding enough charge? it does turn over slow but only when the engines hot

 

I don't think it is a weak battery. Check the voltage with the truck off and running and let us know what you get.