A little fuel gauge help

Discussion in 'Other Auto Tech' started by DrScientist, Mar 13, 2012.

  1. I have an "electrical" question, sort of. Its on a chevy, but this really isn't a "chevy specific" question, more of a basic electrical question in my opinion. I thought I'd ask cause they don't seem to be of much help over at my chevy forums. So here goes.

    I'm wiring up some new gauges on my 87 chevy silverado. I like those old trucks and I figured I'd fix one up. The factory gauges worked quite poorly. I've replaced all the other gauges on the truck successfully, but now I'm on the last one and its giving me trouble. The fuel gauge.

    One of my problems is, that I need to locate the exact point I should solder to on the printed circuit. There is a printed circuit that runs behind the gauges as you can see in the pic. For the fuel gauge, there are only 3 options to solder to. Only 3 possible points, the rest not relevant to the fuel gauge. The factory fuel gauge had only 3 plugs (or prongs) sticking out of the back. These 3 prongs just plug right into the little metal things that attach directly to the printed circuit itself. The metal things just contact the correct spots on the copper in the circuit itself. Pretty simple.

    So I started out by just soldering the new fuel gauge contact points to the printed circuit, in the same formation that the factory gauge used. Both gauges look almost identical on the back. So it would seem that they might use corresponding contact points on the printed circuit. These trucks use zero Ohms of resistance for an empty fuel tank, and 90 Ohms to signify a full tank. For some reason the gauge must be reading far beyond that, cause the needle on it immediately dove down to way past the "Full" mark on the gauge as soon as I soldered it to the printed circuit. It remained there even after I reinstalled everything back into the truck. And I can't really just trace the wire from the fuel tank, cause the truck has two tanks. I have found it very difficult to locate the wire under the hood, that runs to the back of the gauges.

    So am I doing something wrong here? Is there some reason that soldering this won't work? Maybe I am creating too much resistance by soldering? I don't want to just keep guessing and soldering and then desoldering, cause I don't want to ruin my precious printed circuit. I need to get this right the first time. Well, the second time I mean. I can't just keep trying things. Is there some way that I could better use my Ohm meter, to try and find the exact place that I need to hook the new fuel gauge up to, on the printed circuit?

    Below is a picture of the printed circuit to help anyone who might not understand what I'm talking about. All it is, is just very thin copper sandwiched between to sheets of plastic which are of course glued together. There are points that you can solder to, which are exposed.

  2. I understand what you're talking about with the truck. I had an '83 that I fixed up way back when too. Wish I still had it. What I don't get is: why are you trying to use the printed circuit? You should be able to direct wire the fuel gauge to both tanks incorporating the tank switch on the dash. You have to make sure there's a good ground for the gauge and the float otherwise your gauge will "bury" itself. Good luck!
  3. Ok thanks I never thought about using the switch itself. How exactly would you go about doing that? I suck at electrical/signal stuff. Just use the wires going to the switch maybe?