Help a novice with troubleshooting fuel sending unit

[Innoi]

I have a 1969 dodge coronet. I bought the car with no functioning dash gauges. The previous owner put in the triple gauge cluster under the dash. Anyways I need at least a functioning fuel gauge for now. I bought an aftermarket gauge that was specific to Mopar, so the ohm's should be correct. So here is where I am getting frustrated. I climbed under the car and got to my fuel sending unit. Found the stock wire and noticed there was no grounding strap. This is what I did to try to troubleshoot.

First I took off the stock wire and tested the sender in the tank with my multi meter. Held the red to the sending wire post and held the ground onto the metal fuel tube. The meter read about 54 oms. Which I suspect is about right. I filled up last week and drove around so I should of burned about a quarter tank. So I'm thinking good the sender is good and It must be the wiring and ground.

I then ran a jumper wire from my battery to the new gauge, ran a ground jumper wire from the metal fuel tube off the sender to the ground on my gauge, and a jumper wire from the sender post to the gauge. It should of read somehwere about the 3/4 range but it didn't. It actually read empty?? I took the ground off and it read completly full? I tried to ground to the frame to see if i would get a different reading but I got the same, empty reading. I'm stumped at this point. The way the gauge is acting is telling me the sender is broke, but when I tested the sender it seemed to be good. Help Please.

 

[HALIFAXHOPS]

Only real way to test the sending unit is to take it out and full is 10 ohms, mid 23 and empty 73.7 It does sound about right what you are getting though. Did you put 12v to the gauge itself or the wire? It is designed for no more than 5vdc

 

[HALIFAXHOPS]

I am pretty sure the full voltage at the gauge is 3.7 or so I have to check I build testers for the gauges. I do know for sure low is .9

 

[Innoi]

ok I'll try that. Where should I wire the hot lead from? The fuse box? Or is there somewhere else? Can I use a 9v battery just for testing?

 

[HALIFAXHOPS]

NO! If anything first ohm out the fuel gauge make sure the windings are not burned out they should shoe some ohms forgot what not open. They are just some really small copper windings around a piece of bi metal and when they get WARM it flexes and runs the sweep of the meter. If anything use two aaa in series and see if it moves first. If you hit it with 12v it is probably broken.

 

[Innoi]

I double checked the instructions for the gauge and it said connect the hot to a 12v source??? They recommend a switched source so it's not running all the time. I don't think my gauge is broken, something else.

 

[HALIFAXHOPS]

Really what instructions? I can see before it goes through the current limiter that drops the voltage from 12 to 5vdc. Hmm interesting. Oh snap after market gauge right? What ohm sending unit does it recommend. I was thinking factory gauge.

 

[Innoi]

It's the Equus 7361. I got it off if Amazon for 17 bucks.

 

[HALIFAXHOPS]

Can you post the instructions? Why a after market gauage and not the factory one?