Fuel tank selector switch HELP!!

BigPoser

Full Access Member
Joined
May 22, 2015
Posts
169
Reaction score
2
Location
Bakersfield, CA
First Name
Brandon
Truck Year
1973
Truck Model
Cheyenne Super 10
Engine Size
350
I posted this in the TECH DISCUSSION, but may have put in the wrong place.

I need some help in getting the wiring for the fuel tank selector switch that is in the cab correct. I've looked at wiring pics for hours and still haven't found what I'm looking for.

I have a 73 C10 Heavy half ton. It has two saddle tanks. Previous owner had a two position 5 pin toggle switch on the dash. The pass sending unit wasn't even hooked up. I replaced the toggle with a 3 position, 6 pin switch and currently have these wires going to it. It's the position of the wires that I'm unable to get right. Left tank sending unit, Right tank sending unit, power from panel, ground, fuel gauge, and power to the tank switch valve.

Do I even have the right wires going to the switch? If so, where do they go on the switch itself? If not, which wires should be going to the switch? Do I even have the right switch? When I have the ignition on, one tank says it's overfull, and the other is on empty.

I really need help on this and it's very frustrating working on this by myself. I'm really getting upset.

Thanks in advance.

Brandon
 

firebane

Full Access Member
Joined
Jul 10, 2014
Posts
1,732
Reaction score
23
Location
Calgary, AB
First Name
Curtis
Truck Year
1974
Truck Model
K10
Engine Size
350
- Each tank has a single wire for the sender and another for ground
- The fuel switch has a single wire (from what I remember)

The toggle switch should have 5 wires.
1 - Left Tank
2 - Right Tank
3 - To Fuel Gauge
4 - 12v Power
5 - To switching valve

From my understanding is that when power is applied to the switching valve it opens and allows fuel from one tank to flow. When power is taken away the valve closes and the other tank is in operation.

I am in the process of dealing with all this stuff myself and the POs did an AWESOME job hacking it up requiring me to do a bunch of new wiring.
 

BigPoser

Full Access Member
Joined
May 22, 2015
Posts
169
Reaction score
2
Location
Bakersfield, CA
First Name
Brandon
Truck Year
1973
Truck Model
Cheyenne Super 10
Engine Size
350
- Each tank has a single wire for the sender and another for ground
- The fuel switch has a single wire (from what I remember)

The toggle switch should have 5 wires.
1 - Left Tank
2 - Right Tank
3 - To Fuel Gauge
4 - 12v Power
5 - To switching valve

From my understanding is that when power is applied to the switching valve it opens and allows fuel from one tank to flow. When power is taken away the valve closes and the other tank is in operation.

I am in the process of dealing with all this stuff myself and the POs did an AWESOME job hacking it up requiring me to do a bunch of new wiring.


Thank you. So are the numbers you mention also referring to the corresponding positions on the switch as well? I feel you on the wiring. I haaate it. Probably going to have to rewire the whole truck just to make it right.
 

firebane

Full Access Member
Joined
Jul 10, 2014
Posts
1,732
Reaction score
23
Location
Calgary, AB
First Name
Curtis
Truck Year
1974
Truck Model
K10
Engine Size
350
Thank you. So are the numbers you mention also referring to the corresponding positions on the switch as well? I feel you on the wiring. I haaate it. Probably going to have to rewire the whole truck just to make it right.

This is a diagram of a switch layout I found which I'll be using.

You must be registered for see images attach
 

BigPoser

Full Access Member
Joined
May 22, 2015
Posts
169
Reaction score
2
Location
Bakersfield, CA
First Name
Brandon
Truck Year
1973
Truck Model
Cheyenne Super 10
Engine Size
350
This is a diagram of a switch layout I found which I'll be using.

You must be registered for see images attach

Very cool thanks. So it looks like I need to remove the ground wire that I have on my switch and check the grounds on each of my tanks.
 

firebane

Full Access Member
Joined
Jul 10, 2014
Posts
1,732
Reaction score
23
Location
Calgary, AB
First Name
Curtis
Truck Year
1974
Truck Model
K10
Engine Size
350
Yes tanks should be grounded from tank to the frame not to the switch.
 

chengny

Full Access Member
Joined
Feb 22, 2012
Posts
4,086
Reaction score
953
Location
NH
First Name
Jerry
Truck Year
1986
Truck Model
K3500
Engine Size
350/5.7
That's strange, I wrote a fairly detailed response this afternoon - along with the wiring diagram below - and now it's gone! I probably forgot to click on the "post reply" button and shut down my browser. Oh well.


Wiring diagram (actual 1973 version):

You must be registered for see images attach



Curtis is correct here:

From my understanding is that when power is applied to the switching valve it opens and allows fuel from one tank to flow. When power is taken away the valve closes and the other tank is in operation.

This earlier tank switching system incorporated a solenoid activated transfer valve. Power from the fuse block (pink/black lead) comes into the switch on pin 1 and exits on pin 2 (light green) - but only if the contacts are closed.

When the dash switch is in the LH position the 1/2 contacts are open and so there is no power to the solenoid. In this case, an internal spring causes the valve to shuttle to the default position - the LH tank.

If the switch is moved to the RH position the contacts 1/2 close and the solenoid is supplied with 12 VDC - the valve then shuttles to the opposite position and opens the port to the RH tank.

That's the whole valve control circuit description (the solenoid coil is grounded through the valve body and then to the frame).

Level sensing is switched on another set of contacts. The sensing leg of the gas gauge is lead to the switch on the tan wire. It will be connected to whichever tank the transfer valve is lined up to when the switch is moved.

The tan lead comes in on pin 4 and, depending on the switch position, it will exit on either pin 3 or 5.

Pin 3 (light blue) goes to the auxiliary/RH tank.

Pin 5 (tan/white) goes to the production/LH tank.

You guys might need to play around (with your switches and a meter) to figure out how the OEM wiring will need to be connected to the aftermarket switches. But it looks like Curtis' dwg is dead on.

The sensing legs are grounded as with any other gas gauge circuit (sender body to frame).

One thing to take notice of is that the wiring diagram above has an error - and it's not a big deal. The position of the tanks as shown in the dwg is backwards from the actual locations in the truck.
 

firebane

Full Access Member
Joined
Jul 10, 2014
Posts
1,732
Reaction score
23
Location
Calgary, AB
First Name
Curtis
Truck Year
1974
Truck Model
K10
Engine Size
350
Well I'd rather have the left tank as the main "production" tank instead of the right because lets be honest... the right side as a production tank is silly to walk AROUND the truck hahaah.
 

BigPoser

Full Access Member
Joined
May 22, 2015
Posts
169
Reaction score
2
Location
Bakersfield, CA
First Name
Brandon
Truck Year
1973
Truck Model
Cheyenne Super 10
Engine Size
350
That's strange, I wrote a fairly detailed response this afternoon - along with the wiring diagram below - and now it's gone! I probably forgot to click on the "post reply" button and shut down my browser. Oh well.


Wiring diagram (actual 1973 version):

You must be registered for see images attach



Curtis is correct here:

From my understanding is that when power is applied to the switching valve it opens and allows fuel from one tank to flow. When power is taken away the valve closes and the other tank is in operation.

This earlier tank switching system incorporated a solenoid activated transfer valve. Power from the fuse block (pink/black lead) comes into the switch on pin 1 and exits on pin 2 (light green) - but only if the contacts are closed.

When the dash switch is in the LH position the 1/2 contacts are open and so there is no power to the solenoid. In this case, an internal spring causes the valve to shuttle to the default position - the LH tank.

If the switch is moved to the RH position the contacts 1/2 close and the solenoid is supplied with 12 VDC - the valve then shuttles to the opposite position and opens the port to the RH tank.

That's the whole valve control circuit description (the solenoid coil is grounded through the valve body and then to the frame).

Level sensing is switched on another set of contacts. The sensing leg of the gas gauge is lead to the switch on the tan wire. It will be connected to whichever tank the transfer valve is lined up to when the switch is moved.

The tan lead comes in on pin 4 and, depending on the switch position, it will exit on either pin 3 or 5.

Pin 3 (light blue) goes to the auxiliary/RH tank.

Pin 5 (tan/white) goes to the production/LH tank.

You guys might need to play around (with your switches and a meter) to figure out how the OEM wiring will need to be connected to the aftermarket switches. But it looks like Curtis' dwg is dead on.

The sensing legs are grounded as with any other gas gauge circuit (sender body to frame).

One thing to take notice of is that the wiring diagram above has an error - and it's not a big deal. The position of the tanks as shown in the dwg is backwards from the actual locations in the truck.


Thank you very much. I'm getting ready to tackle this now and have another question. Does the switch have to be a 2 position or can it work with a 3 position switch?
 

firebane

Full Access Member
Joined
Jul 10, 2014
Posts
1,732
Reaction score
23
Location
Calgary, AB
First Name
Curtis
Truck Year
1974
Truck Model
K10
Engine Size
350
Thank you very much. I'm getting ready to tackle this now and have another question. Does the switch have to be a 2 position or can it work with a 3 position switch?

It is best to use a DPDT switch.
 

BigPoser

Full Access Member
Joined
May 22, 2015
Posts
169
Reaction score
2
Location
Bakersfield, CA
First Name
Brandon
Truck Year
1973
Truck Model
Cheyenne Super 10
Engine Size
350
Ok so I have everything wired up correctly as the diagrams show. Still showing over full on the gauge. I redid the grounds on both tanks too. Something to note though, is that when I use a test light and touch each of the tank wires or the gauge wire, I get a pretty faint light, which would mean that each of them are getting power, but not enough? I'm not exactly sure. If I hold the light on each of the wires long enough, it looks to make the gauge work correctly for each tank as I'm pretty sure that they only have about an eighth of the tank.

I can't find my multi-meter either and that's only adding to the frustration.
 

chengny

Full Access Member
Joined
Feb 22, 2012
Posts
4,086
Reaction score
953
Location
NH
First Name
Jerry
Truck Year
1986
Truck Model
K3500
Engine Size
350/5.7
X 2 -

A DPDT (2 position) switch has all the switching capability you'll need to wire this circuit.
Plus it will be cheaper, less complicated to make connections to and easier to find.

If I were you guys I would source a decent heavy duty switch - and I would spring for the extra couple of bucks and get one with two color illumination:

Seadog 4202531 Red/Yellow Illuminated Rocker Switch - DPDT - On/Off/On $7.95

You must be registered for see images attach


http://www.boatersland.com/sdg4202531.html

But whatever switch you decide on, remember that it has to be a rocker style switch. It can't be a momentary switch. If it was momentary the instant you let your finger off of it, the tank valve would shift back to the production tank.

The later transfer valves were motor operated and the switch had to be held for a second or so to power the valve over to the other tank. But after that, it would stay in whatever position the operator left it in - until it was powered back in the other direction.
 

chengny

Full Access Member
Joined
Feb 22, 2012
Posts
4,086
Reaction score
953
Location
NH
First Name
Jerry
Truck Year
1986
Truck Model
K3500
Engine Size
350/5.7
Ok so I have everything wired up correctly as the diagrams show. Still showing over full on the gauge. I redid the grounds on both tanks too. Something to note though, is that when I use a test light and touch each of the tank wires or the gauge wire, I get a pretty faint light, which would mean that each of them are getting power, but not enough? I'm not exactly sure. If I hold the light on each of the wires long enough, it looks to make the gauge work correctly for each tank as I'm pretty sure that they only have about an eighth of the tank.

I can't find my multi-meter either and that's only adding to the frustration.


Pull the sensing lead off the sender and try these two tests;

1. If the tan/white (or light blue) wire to the sender is broken/disconnected the control leg exerts the greater force and pegs the gauge needle to Full.

2. If the tan/white (or light blue) wire is allowed to contact ground (before passing through the sender), the sensing leg has a greater force and the gauge pegs low.

If those two things happen, it will at least confirm proper operation of the gas gauge.
 

firebane

Full Access Member
Joined
Jul 10, 2014
Posts
1,732
Reaction score
23
Location
Calgary, AB
First Name
Curtis
Truck Year
1974
Truck Model
K10
Engine Size
350
Ok so I have everything wired up correctly as the diagrams show. Still showing over full on the gauge. I redid the grounds on both tanks too. Something to note though, is that when I use a test light and touch each of the tank wires or the gauge wire, I get a pretty faint light, which would mean that each of them are getting power, but not enough? I'm not exactly sure. If I hold the light on each of the wires long enough, it looks to make the gauge work correctly for each tank as I'm pretty sure that they only have about an eighth of the tank.

I can't find my multi-meter either and that's only adding to the frustration.

Yeah your going to need your multimeter for this to work effectively.

You will want to ensure your sending units are working correctly and you can either do this directly at the tank itself or take the wire for the tank off the switch and ohm it.

If my memory is correct your tanks should be 90ohm senders meaning that when the tank is full it will read at 90ohms and as it gets closer to empty it'll drop down in numbers. A half tank of gas will read some where in the 45 ohms area.
 

chengny

Full Access Member
Joined
Feb 22, 2012
Posts
4,086
Reaction score
953
Location
NH
First Name
Jerry
Truck Year
1986
Truck Model
K3500
Engine Size
350/5.7
He's got something going on - probably with either the gas gauge or the common sensing leg between the gauge and the switch. His test probe should light right up.

Something to note though, is that when I use a test light and touch each of the tank wires or the gauge wire, I get a pretty faint light, which would mean that each of them are getting power, but not enough?
 

Forum statistics

Threads
35,557
Posts
748,095
Members
24,482
Latest member
JohnC
Top