dual tank wont.switch..first step?

[NASTY-LSX]

The switch on the dual tank is not working on my 85.
Whats are the first few steps to look for besides the fuse?
I would really like to fix this problem. THANKS!!!

[8lugnutz]

There are quite a few threads on this subject:

http://67-72chevytrucks.com/vboard/s...d.php?t=512849

There is a diagram here too

Forum member Hatzie has wiring schematics for most of these trucks at the below link:
1973-1991 GM Light Truck Service, Unit/Overhaul, & Wiring Manuals in PDFhttp://67-72chevytrucks.com/vboard/s...d.php?t=545416

[83GMCK2500]

Which style switch do you have? Early ones were a solid click back and forth, the later ones are a momentary and have a softer rocking motion (also say Depress Fully on bottom of bezel). The early style is prone to failure, momentary are not. I found a good troubleshooting guide once, will look for again.

[NASTY-LSX]

Thanks 8 lug n 83 GMC I really appreciate it as far as having an early model or newer one, I don't know I have 85 model I will take a picture and post it thanks

[8lugnutz]

Early models had the on/on switch (mine is an '80 and has this type). Later models, including my '86 crew cab, had the "depress fully" type switch. I think yours will have the same type switch as my crew.

I recently went through the same thing you are going through on getting both tanks to work, there are lots of threads on this forum with information. Your truck probably has the 5 pin type valve (I am guessing because of the '85 year model), check out the diagram in the links I posted.

As Devin stated above, there is a really good troubleshooting guide in one of these threads, I ran across it when I was researching my troubles, but I couldn't find it either :-(

[NASTY-LSX]

Originally Posted by 8lugnutz

Early models had the on/on switch (mine is an '80 and has this type). Later models, including my '86 crew cab, had the "depress fully" type switch. I think yours will have the same type switch as my crew.

I recently went through the same thing you are going through on getting both tanks to work, there are lots of threads on this forum with information. Your truck probably has the 5 pin type valve (I am guessing because of the '85 year model), check out the diagram in the links I posted.

As Devin stated above, there is a really good troubleshooting guide in one of these threads, I ran across it when I was researching my troubles, but I couldn't find it either :-(

Yup, mines says depress fully

[custom97]

Great information

[83GMCK2500]

Did you find the electrical diagnosis on here yet? When you fully depressed the switch either way does the fuel gauge move?

EDIT, with the key on and every accessory off I can hear my selector valve actuate when I switch my tanks. Can you? Was thinking there might be a blockage/failure with the valve.

[NASTY-LSX]

Originally Posted by 83GMCK2500

Did you find the electrical diagnosis on here yet? When you fully depressed the switch either way does the fuel gauge move?

EDIT, with the key on and every accessory off I can hear my selector valve actuate when I switch my tanks. Can you? Was thinking there might be a blockage/failure with the valve.

I'll try that tomorrow. Thanks

[86swb]

Why do you need two tanks anyway? Cost to much just to fill one tank. Unless you are planning on a long trip. I only use the driver side tank and I am one of those guys who likes everything that is suppose to work to work. But I do not care of the right tank works or not. MO

[NASTY-LSX]

Originally Posted by 86swb

Why do you need two tanks anyway? Cost to much just to fill one tank. Unless you are planning on a long trip. I only use the driver side tank and I am one of those guys who likes everything that is suppose to work to work. But I do not care of the right tank works or not. MO

because I want to have everything working properly thats suppose to be working properly!!!!

[83GMCK2500]

Originally Posted by NASTY-LSX

because I want to have everything working properly thats suppose to be working properly!!!!

Amen to that! I don't know about you but up in little ol' WA I need both tanks to get all the way across the state, is kinda nice to be able to do.

[86swb]

Like I said "Unless you are taking a long trip". But as far as I know, you do not see any more of the double tanks on todays trucks. As far as I know. I also like everything working that is suppose to work. I just very rarely use it. But every now and then when the driver side tank gets low I do fill up the right tank and use it just to keep it in good working order. I think the 80's was the last years for the double tanks. If I am wrong, let me know.

[NASTY-LSX]

Originally Posted by 86swb

Like I said "Unless you are taking a long trip". But as far as I know, you do not see any more of the double tanks on todays trucks. As far as I know. I also like everything working that is suppose to work. I just very rarely use it. But every now and then when the driver side tank gets low I do fill up the right tank and use it just to keep it in good working order. I think the 80's was the last years for the double tanks. If I am wrong, let me know.

Yup I hear ya. Do you know what the fill capacity of the 85 tanks were?...
I like the fact that when I pull up to the gas station I have the option to fill either
Side depending on what pumps are available lol.

[hatzie]

Newer trucks like My 2000 GMC have options for larger tanks. Mine has around 30 gallon capacity.

There's absolutely no need to use a Polarity Reversing Momentary MON-OFF-MON switch with any of the square body trucks.
The Polarity Reversing ON-ON switch that's listed by the parts stores for 87-91 RV series TBI GM trucks is AC Delco D7089C. It works for all the 81-86 CK and 87-91 RV squares.

All dual tank 81-86 CK and 87-91 RV squares used the exact same Pollack motorized tank selector valve. The valve assembly has internal switching and diodes that park the motor when it reaches the end of its' travel.

To answer your question... Usually the switch gets dodgy. They can be disassembled, cleaned up, and lubed... but at $12-$20 for a replacement why bother.

Grab a meter and;
1 Check that power is present between Pink and Black wires at the switch plug with the ignition on.
2 Check the switch itself is working properly. If it's the equivalent of the Standard Motor Products DS293 momentary switch that says "depress fully" buy the Delco 7809C and save yourself a headache.

My Polarity reversing tank Switching explanation..

[hatzie]

Fill capacity could be 16 or 20 gallons on each side depending on how it was optioned.

[83GMCK2500]

For a longbed if the tanks extend rearward up to the forward rear leafspring hanger they are 20s. If they are 10-12" from it, they are 16s.

[NASTY-LSX]

Originally Posted by 83GMCK2500

For a longbed if the tanks extend rearward up to the forward rear leafspring hanger they are 20s. If they are 10-12" from it, they are 16s.

Thanks, I have 20 gallon tanks. It stops right at the hanger

[83GMCK2500]

Awesome, I wish I did, but as close as I am to my LS I am thinking rear mount Blazer/'burban now.

How comes your switching diagnosis?