Fuel gauge on dual tank

[stumpjumper]

Hi Folks,

I've had my 'new' truck for a few weeks now, it's a '73 Cheyene Super K20 with a 350. Not much to look at but it runs like a champ. I finally had a chance to poke around on the truck this weekend.  There are a few mechanical issues but not bad for a 34 year old machine.

I will probably have lots of questions for you experts but first on my list is making the fuel gauge and tank selector work. I did tear into it this past weekend using the suggestions from past posts on this group but without a decent schematic I'm lost as to what is supposed to work how. I tried to check the resistance of the wires from the senders but there is no reading (infinity) on these wires at the transfer switch. I expected to find something between 0 and 90 ohm at one of the terminals behind the gauge but I found a ground, a full 12 volt supply and a lesser voltage on the other pin. The gauge itself is pegged at WAY past full.

So...my first question, does anyone know where I can download a decent electrical schematic for the dual tank/switch/gauge system?  There is nothing I could find in either Haynes or Chilton. Don StClair posted a schematic back in 2006 but it's too small for my old eyes.

Any help finding a schematic would sure be appreciated.

Thanks,
Lewis

[VileZambonie]

If you checked from the switch to ground and got infinity that means it's not shorted to ground which is a good thing. Start at the source- if it was a tail light that was out where is the 1st place you'd go? The tail light right? So treat all your electrical problems the same way- check the source and it's connections. I would pull the wire off of the sending unit and put it to ground to see if it moves the gauge first. If nothing happens try it at the connection under the cab where it jumps to the other tank. If still no movement on the gauge check the gauge itself. I believe I've posted this schematic quite a few times also.

[VileZambonie]

[Captkaos]

test

[DnStClr]

If the gauge is past full, it's probably a bad sending unit or a dirty connection. If you take the connector apart at the switching motor/valve, and read across the two pins on the connector going to the tank, there shouldn't be more than 90 ohms. That reading indicates a full tank. A reading of infinity indicates a shorted circuit. After some years,the tank float can fail and fill with fuel, so you lose the resistance in the circuit and have to replace the sender.  Mine came apart and gave the same reading. 

[VileZambonie]

A reading of infinity indicates a shorted circuit. 

You mean "open circuit" not shorted.

[DnStClr]

Yes I do. Thanks. I posted at 2am and was pretty Zonked after work. (10 hr.night shift guy).