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HotRodMan 01-05-2013 09:34 PM

New gas sending unit not working?
Working on a 1930 street rod 350 engine with "Tanks" U2-SS gas tank in the trunk. Previously the car had a floatless sending unit in the gas tank. It worked fine for about 10 months then went bad. The wiring for the floatless sending unit consisted of 2 grounds, 1 wire from the gas gauge, and 1 hot wire from the fuse panel, total of 4 wires. Gas gauge and wire is new.

We have decided to replace this with a universal "old style" sending unit with a float, model number SN-35. This is a brand new sender and there are no directions telling you how to wire it up. The top of the SN-35 unit only has two terminals. I connected the wire from the gas gauge to the center terminal (goes to reostat), and a ground wire to the other terminal on the mounting flange. I have the sending unit out of the tank and with the ignition switch in the on position, I am moving the float up and down but I am not getting any reaction on the gas gauge at all.

Can someone tell me what I am doing wrong?

EOD Guy 01-06-2013 05:40 AM

Is the ohm resistance of the sending unit a match for the gauge you are using?

darrin502 01-06-2013 09:01 AM

Gasage problem
wired gas gages work on Ohm principle. You will have to find out the ohm rating of your gage and then match the float assembly with that also with the sending unit out of the tank make sure you have the sending unit grounded to the chassis of the car.
It might be 0-25 or 10-30 etc.
Hope that helps

HotRodMan 01-06-2013 11:35 AM

Sending unit and gauge match
Yes the sending unit and gas gauge match. This is a 33-240 ohm matched set.

darrin502 01-06-2013 12:07 PM

If u can take and wire the gage and the float unit direct to the battery not thru the ignition sw & it works then u have a prob in the car wiring and if it doesnt work then it is in the gage or sending unit. Try going from the gage To ground and the gage should peg that will give a good test for the gage. Ground the wire going to the tank.

HotRodMan 01-06-2013 04:34 PM

No voltage at gas gauge
OK I found the problem. I took a volt reading at the gas gauge with the key turned on and did not get any voltage. The wire that feeds the gauge comes from a switched terminal on the fuse panel. I checked the fuse panel and got a reading so I knew then the wire was bad. I fished the wire out of a spegetti network of wireing and discovered a rodent had chewed the wire in two. I installed a new wire from the fuse panel to the gauge and it works great now. Thanks to all who responded.

darrin502 01-06-2013 04:42 PM

Glad u got it. Electric probs can be a pain.

EOD Guy 01-06-2013 06:32 PM

Good to hear it was an easy fix

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