Another dual tank/guage problem

[Starliner]

Today I replaced the front tank sender which i confirmed to be ng.

I also checked the new one prior to installing it.

Also today i dropped my rear tank (which had a new, working sending unit), just to replace the filler hose.

All buttoned up, on my way to the gas station and the front showed empty, (as it was), and the rear showed just off empty because of the 2 gallons that were still in it.

Driving from the gas station and both tank show as empty now.

I kept switching back and fourth but nothing showed. I tried key on/off but still no go.

I checked diagrams and I cant figure out how the 5 volts gets to the sending units or where they ground, nor can I tell if the tank selector switch has any interaction with the sending units-to-guage.

Not sure if fuse 15 has any purpose besides switching the tank valve.

Of course tomorrow I will take a volt meter to fuse #15 but any other ideas please shoot them my way.

I realize this is a popular topic but couldnt find the answer.

Sorry, wish I could have met the show deadline.

[ArdWrknTrk]

The instrument cluster voltage regulator pulses the D.C. voltage of the truck to create an 'average' 5.5V or so.

The cluster flex circuit routes this through the gauge and out to the tanks.

Depending on your system (ill have to check) the fuel switching valve changes which sender is connected.

Power goes through the sender (rheostat) and then to ground.

So, the sender is limiting power through the gauge from the ground side.

If you have a functioning oil pressure or water temp, then the problem is not power.

[ArdWrknTrk]

The instrument cluster voltage regulator pulses the D.C. voltage of the truck to create an 'average' 5.5V or so.

The cluster flex circuit routes this through the gauge and out to the tanks.

Depending on your system (ill have to check) the fuel switching valve changes which sender is connected.

Power goes through the sender (rheostat) and then to ground.

So, the sender is limiting power through the gauge from the ground side.

If you have a functioning oil pressure or water temp, then the problem is not power.

Yep.

Here is pg 106 from the EVTM.

Ground 701 is behind the instrument panel, near the right of the radio.

[Gary Lewis]

Joe - First, get me the entry info today and I'll get it in.

Jim - I get lost, as you know, in what fuel systems where used when. Are you sure Joe's '84 will have that fuel system setup? I would have thought that his '84 w/a 351W would have this setup:

[ArdWrknTrk]

Joe - First, get me the entry info today and I'll get it in.

Jim - I get lost, as you know, in what fuel systems where used when. Are you sure Joe's '84 will have that fuel system setup? I would have thought that his '84 w/a 351W would have this setup:

Is there no egg on your face smiley???

So perhaps it is the switch in the climate control bezel that is faulty.

Or connector 208.

But it's definitely not the fuse, if the other gauges function.

[Gary Lewis]

Is there no egg on your face smiley???

So perhaps it is the switch in the climate control bezel that is faulty.

Or connector 208.

But it's definitely not the fuse, if the other gauges function.

I agree that the fuse powering the gauges themselves is working. So it must be something else that is in common with both tanks, and that does suggest the switch or the connector.

[Starliner]

I agree that the fuse powering the gauges themselves is working. So it must be something else that is in common with both tanks, and that does suggest the switch or the connector.

Guys I really appreciate the thoughtful response.

Back to work.

[Machspeed]

Guys I really appreciate the thoughtful response.

Back to work.

Following this thread closely, as I too have no fuel gauge readings. Several years ago did what you did and replaced both sending units. I had the bed off when I did this and the gauges seemed to work fine. I could move the floats and watch the gauge move. And, they seemed to be where they needed to be based off the amount of fuel in the tanks. However, when I put the bed back on, I noted no readings. Haven't had a working fuel gauge in years. Time to fix! Please keep us advised on your hopeful fix?

[Starliner]

Following this thread closely, as I too have no fuel gauge readings. Several years ago did what you did and replaced both sending units. I had the bed off when I did this and the gauges seemed to work fine. I could move the floats and watch the gauge move. And, they seemed to be where they needed to be based off the amount of fuel in the tanks. However, when I put the bed back on, I noted no readings. Haven't had a working fuel gauge in years. Time to fix! Please keep us advised on your hopeful fix?

Sure will.

Thanks to the guys I now understand that:

If the other guages work I am getting ground,

Also,

Going to the sending unit should be around 5.5v and that, or less going back to the guage.

These guys know their stuff.

[ArdWrknTrk]

Sure will.

Thanks to the guys I now understand that:

If the other guages work I am getting ground,

Also,

Going to the sending unit should be around 5.5v and that, or less going back to the guage.

These guys know their stuff.

Note that you will see pulsing voltage on the sender wire.

The ICVR acts like a very fast flasher module.

Also you will see the zigzag line between the 'N' and ICVR in the diagrams above.

That is a resistor used to limit current applied to the instruments.