1987 R20 Dual Tank wiring

[zieg85]

I am just starting to get into this 87 R20 I recently got and have a question about the dual tank switch wiring.  Whomever before me removed the switch.  It is 4 wires and I need to know if by jumping 2 of them will the gas gauge start working or is the gauge wires somewhere else.  This is my first dual tank TBI truck and haven't a clue how this is wired to switch the tanks.  Thanks in advance

[bd]

The tank selector switch reverses polarity to the selector valve motor; nothing more.  The dash gauge switches between tanks by the selector valve.  Three pink wires connect to the selector valve: pink/black (right tank sender), pink/white (left tank sender) and solid pink (gauge).  Splicing pink to either pnk/blk or pnk/wht will hardwire the gauge directly to the respective tank sender.

[zieg85]

Thanks Rich, I knew you'd come through.  Now I have to figure out which tank is running.  Time to call my cousin to come over to turn the key while I lay under the truck with my hands on each tank.

[bd]

Oops!  The above diagram is for pre-TBI tank wiring.  The selector switch also powers the respective in-tank pumps on TBI equipped vehicles.  Connections are nearly the same with the exception that the dark green and light green (tan and gray on TBI equipped vehicles) selector valve motor wiring extends to the pumps too....

[zieg85]

Oops!  The above diagram is for pre-TBI tank wiring.  The selector switch also powers the respective in-tank pumps on TBI equipped vehicles.  Connections are nearly the same with the exception that the dark green and light green (tan and gray on TBI equipped vehicles) selector valve motor wiring extends to the pumps too....

Thanks, I am lost when it comes to wiring.  Not having a switch and the truck is running on whatever tank is normal? 

[bd]

Thanks, I am lost when it comes to wiring.  Not having a switch and the truck is running on whatever tank is normal? 

Since the selector valve is motorized, there is no "default" tank.  Fuel is supplied by whichever tank was last successfully selected.

Do you have trouble interpreting wiring diagrams or the logic behind wiring in general?

[zieg85]

OK I just finally got under the truck to see what has been done.  The selector valve---gone.  Right hand tank, completely disconnected.  Left hand tank has a grey wire with a black tracer and a brownish/tan wire, both are not connected to anything.  Thoughts?

[bd]

Are you saying the tan and gry/blk come directly from the left tank pickup unit?  Post a pic.  Usually, tan connects to the left side in-tank pump motor and gray connects to the right in-tank pump motor. 

[zieg85]

Are you saying the tan and gry/blk come directly from the left tank pickup unit?  Post a pic.  Usually, tan connects to the left side in-tank pump motor and gray connects to the right in-tank pump motor.

Here is a picture of both sides.  I haven't seen if either has power with the key on or what happens if I ground either ones or connect them together.

[bd]

It's been cobbled for sure.  See what's hidden under all that tape.  From the factory, gray and tan are fuel pump power to the right and left tanks, respectively.  The chassis side sender wiring is pink with a tracer.

[zieg85]

Thanks

[zieg85]

Should two wires be jumped on the selector switch in the dash so it knows which side is going?  The ground seems tight.

[bd]

Unless the factory switch has been unplugged or repurposed, it is connected through four wires to 12-volt power via the fuel pump relay (tan/wht), ground (blk), both in-tank pumps and the fuel selector valve (tan - left tank & selector valve, and gray - right tank & selector valve).  The dash switch controls directly which pump receives power, as well as, motoring the tank selector valve located under the cab between the left and right tanks.  The tank selector valve switched the dash gauge between the two tanks. 

In effect, if you plan on abandoning future reinstallation of dual tanks and running the truck only off the left side, you need to see 12-volt ignition power on the tan wire running to the left in-tank pump and splice the solid pink wire that once-upon-a-time connected the instrument cluster fuel gauge to the selector valve directly to the pnk/blk wire running to the left fuel tank sender.  Am I making sense?

[zieg85]

Unless the factory switch has been unplugged or repurposed, it is connected through four wires to 12-volt power via the fuel pump relay (tan/wht), ground (blk), both in-tank pumps and the fuel selector valve (tan - left tank & selector valve, and gray - right tank & selector valve).  The dash switch controls directly which pump receives power, as well as, motoring the tank selector valve located under the cab between the left and right tanks.  The tank selector valve switched the dash gauge between the two tanks. 

In effect, if you plan on abandoning future reinstallation of dual tanks and running the truck only off the left side, you need to see 12-volt ignition power on the tan wire running to the left in-tank pump and splice the solid pink wire that once-upon-a-time connected the instrument cluster fuel gauge to the selector valve directly to the pnk/blk wire running to the left fuel tank sender.  Am I making sense?

I will read it about 10X and it may sink in.  The in dash switch is removed and the plug is just hanging there, nothing jumped.  I was working on other aspects of the truck so it is out of the shop and I haven't untaped that picture.  Based on what was done for whatever reason I am OK with the single tank running.  I would just like to get the gas gauge working.  I have been driving it on the country roads and am really liking this TBI 350/700R4/3.73.  It scoots right along and it has been a while since I drove anything with a 700R4.

I just looked at the wiring again above.  Should the tan 920 and tan/white 120 be connected since the switch is no longer in play?

[bd]

I just looked at the wiring again above.  Should the tan 920 and tan/white 120 be connected since the switch is no longer in play?

Yes.  And for the gauge, pink 30 should connect to pink/white 930.