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Posted

I'm in the middle of 12 volt conversion on my 40 P9 and am stuck at the fuel gage wiring. I have installed the 12 to 6 volt runtz, from 5th Ave Garage, on the IGN SW terminal and ran the ignition feed wire to it. For those who have already done this conversion, how do I wire from Fuel Gauge Poles 1 & 2 to the Sending unit(Both original). My  kit only has 2 wires for Fuel Gage. 1 wire goes to the gage and the other wire to the sender. I could use some help here. Thanks in advance. My gage is exactly like the picture attatched.

post-7346-0-30459200-1456930685.jpg

Posted

1 and 2 go the the sending unit. The runtz goes between the ignition switch and the terminal marked ign. There have been comments that the gauge will function properly on 12v. The gauge actually works by resistance heating of the metallic strips behind the gauge. The service manual even tells how to adjust the gauge.

Posted

Look carefully at the rerminals at the sending unit.  One of them is bigger than the other. You might even be able to pick up the numbers there also   Unless they have been messed with the wires the wire  trrminals should be sized according to what terminal it goes to on the sending unit..  If it's similar to the post war setup.

Posted

you will need to run a wire from terminal 1 on the sender to the terminal 1 on the gauge…..and run another wire from terminal 2 on the sender to the terminal 2 on the gauge.   You  need to ensure you have a good ground at the tank to chassis.  The problem with 95% of the old original sender units lie in no or unstable grounds as the wiper that divides the resistance to each terminal takes both terminal to ground through the housing by means of a pressure spring inside the cup riding in a small ball socket.  These sockets get rusted and makes poor and intermittent grounds.  Verify your wiper can take each post smoothly to ground.  Again, operation depends on this ground...the circuit is not completed without this and improper gauge readings/errors will result.   Correct resistance across sender terminal 1 and 2 is approx. 28-32 ohms.  If you move the wiper (float arm)  the resistance values will change.  For an example if terminal 1 now reads 12 ohms in X position then the terminal 2 must read 18 for that optimum 30 ohms total resistance.  This reading must be smooth and with non intermittent resistance at all time on each terminal.  The gauge is designed to pull the needle in both directions at the same time and that combined with a functioning built in 5 volt regulator of the gauge keeps the needle rock steady even with sloshing fuel in the tank as it is a slow reacting circuit.  

  • 4 weeks later...
Posted

I am facing the same problem as Joeys41. I bought an aftermarket 2 terminal fuel sending unit which is a repro of an original unit. The terminals are not marked 1 and 2, and they are both the same size. So I am going to run wires from the sender to my original gauge. I am hoping that I get lucky and connect the wires to the correct terminals...I have a 50/50 change of getting it right...Is there a way to confirm which wire goes to which terminal, or does it matter???Thanks in advance for the help!

Posted

Hey Cold Blue,

Connect the wires before putting the sender in the tank. Put the float to down or empty and check the gage. If it reads other than empty reverse the wires and check again. Or put the float to full and check. Either way it is an easy fix. Then mark the terminals on the sender put it in the tank and hook it up.

 

Joe Lee

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