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Thread: RT79 '72 Mark II Wonky Fuel Gauge

  1. #1
    Junior Member
    Join Date
    Nov 2012

    RT79 '72 Mark II Wonky Fuel Gauge

    Howdy gang,

    My 72 Corona Mark II Wagon's fuel gauge has started acting weird. It now will just shoot straight up all the way past FULL and wiggle a bit and then stay there. I've been having to do mileage tracking in the mean time :-).

    Any thoughts as to whether the gauge is tits up or possibly a short (or bad tank sensor)?

  2. #2
    Junior Member
    Join Date
    Apr 2009
    Portland OR

    Re: RT79 '72 Mark II Wonky Fuel Gauge

    Could be either a bad ground, guage or fuel sender. I'd start with checking your ground at the sender. Most get ground from mounting screws, so if those are rusty and gummed up you may have an easy fix. Turn on the key and have someone create a good ground while y watch the guage. If it finds its appropriate level, problem solved. Next step is to check your sender by pulling and testing it. First visually inspect the rheostat. This is the strip of thin wire on the main body of the sender which the opposite end of the float arm interacts with. As I've been told as far as the oporation of these goes, as the fuel level drops, the float arm contact travels up the rheostat shortening the circuit length and increasing electrical resistance which the guage reads as a change in fuel level. If this tiny wire has broken high up I believe it will automatically peg out the guage until the contact hits it and completes the circuit, giving an accurate reading. Pull your fuel sender out of the tank and first see if the rheostat is broken anywhere (look carefully, the wire is tiny). If no break is readily evident, attach some jumper wires long enough that you can hold the sender and sit in the driver seat. Then with the key on, SLOWLY move the float arm from top to bottom and watch the guage. Once you find where the needle's action becomes erratic/out of the ordinary, and you've done it a few times to be sure of that position, take a look at the rheostat again and you'll probably see a break. You could always just find a good one and swap it in to see if that fixes the problem as well, I just like to determine the actual issue myself before I throw parts at it. If you have a good ground and sender, make sure the guage wiring is tip top, then have the guage tested. Good luck!

  3. #3
    Junior Member
    Join Date
    Nov 2012

    Re: RT79 '72 Mark II Wonky Fuel Gauge

    Thank you for the great response! I'll be sure to post here when I get it resolved (whenever I get the time to actually troubleshoot it!)

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