|
Dear Rod, sorry I cant exactly answer your questions as to which gauge or sending unit you have to buy, but can toss out some theory of operation (if its the type gauge I think it is??) and maybe we can figure it all out. On some general purpose DC Voltage gas gauge and senders, they work by applying power to one of the gauge terminals (when ignition is turned on)while the other terminal leads to the tank sender which is nothing more than a variable slidign resistor, and it completes the circuit to ground because the opposite end of the sending unit (after its resistor) is grounded either directly through the tank or an external ground wire. That way as the fuel level fluctuates and the senders float rises up or down, the difference in resistance causes a different deflection in the fuel gauge needle. Now, the gauge may be a galvo magnetic field type, which means the current flow through it (a coil of wire) causes a magnetic field which deflects a metal needle. (Amount of deflection dependant on amount of current dependant upon resistance of sender) If so, if the current is flowing in the wrong direction (i.e. pos or neg grnd) the needle may not deflect properly, because the direction of current flow also determines the magnetic field polarity (North or South). Other (non magnetic) gauges are bi-metallic type where the difference in curent through them just causes different heat which expands or contracts metal different and direction of the current wouldnt matter in that type of gauge. THEREFORE, if you hook up the gauge to the sender, and with the sender not yet in the tank (so you can move it and see what the gauge does) and it moves to just the opposite of what it should (should obviously go full when sender float at top and empty when float at bottom), it must have to be a correct pos or neg grnd gauge, but I dont see why, as you asked, the sending unit should make any difference whatsoever, as its only a non polarity sensitive passive variable resistor. Also, if the sending units resistance is not a match for the gauge, it could either not deflect much at all (too much resistance) or peg full (too little resistance) and agian youre out of luck. If they are too little, I add external resistance to make them work, but if they are too much resistance, thats not a quick cheap possible jury rig of a fix. If your gauge pegs to empty like you said, my guess is it a galvo type and NOT the correct polarity, (wont work) because if you ground out most gauges, they usually go to full (max current flow) or stay on empty if no power or resistor is an open circuit or they arent grounded properly. Whether or not the sender will work is not because of proper polarity (it has none) but whether or not its resistance matches that needed by the gauge. If the senders mounting frame is electrically isolated from case ground and connects only via its external lug and the ground wire you mentioned, it might be possible to feed it hot there and let the opposite end of the gauge be ground to make it work ASSUMING THE RESISTANCE OF THE SLIDER IS RIGHT FOR THE GAUGE AND THE GAUGE IS INDEED POLARITY SENSITIVE AND OPPOSITE FROM WHAT YOU HAVE. Thats the kind of thing I might try myself but am not gonna officially recommend it here on this board lol. Let us know, Ol John T Nordhoff in Indiana
|
