Press and hold fuel tank switch?

[bennylava]

I'm hoping someone here can explain the difference between the two types of fuel tank switch. I bought a GM brand replacement switch, because the old one died. But it was so difficult to plug in, that I thought maybe I bought the wrong one.

Since they're so cheap, I went ahead and got a Dorman brand one and it fit great and works great.

I noticed that the GM is the press and hold style switch, while the Dorman has no such function. You just flip it one way or the other. What's the difference here? Did the seller perhaps ship me the wrong GM brand switch? Maybe my 87 truck isn't supposed to have that kind of switch, and that explains why it didn't fit the socket.

It looked like the pins lined up, but I couldn't get them to go in. Wasn't going to try and force it and break something. Thanks!

[Dleslie212]

Originally Posted by bennylava

I'm hoping someone here can explain the difference between the two types of fuel tank switch. I bought a GM brand replacement switch, because the old one died. But it was so difficult to plug in, that I thought maybe I bought the wrong one.

Since they're so cheap, I went ahead and got a Dorman brand one and it fit great and works great.

I noticed that the GM is the press and hold style switch, while the Dorman has no such function. You just flip it one way or the other. What's the difference here? Did the seller perhaps ship me the wrong GM brand switch? Maybe my 87 truck isn't supposed to have that kind of switch, and that explains why it didn't fit the socket.

It looked like the pins lined up, but I couldn't get them to go in. Wasn't going to try and force it and break something. Thanks!

From what I understand, it's based on which tank selector valve you're using. The old style, three port valve only needs voltage when one tank is selected. When no voltage is present, it automatically reverts to the default tank, which I think is passenger side.

The newer six poet valves need momentary voltage to switch which tank it's drawing from, but then they stay on that tank until switched again.

[Just call me Sean]

'87 up would have electric fuel pumps.

[Dead Parrot]

Originally Posted by Dleslie212

From what I understand, it's based on which tank selector valve you're using. The old style, three port valve only needs voltage when one tank is selected. When no voltage is present, it automatically reverts to the default tank, which I think is passenger side.

The newer six poet valves need momentary voltage to switch which tank it's drawing from, but then they stay on that tank until switched again.

Pretty much what I understand as well, except there were some 6 port solenoid valves that use the simple flip switch. Replacement 3 port valves are still available while the 6 port are unobtainium unless you are lucky in a salvage yard or resale site. Because of that, there are several swap threads on here that address changing from the solenoid type to the motorized type.

The newer motorized 6 port valves need the press and hold switch to allow the motor to swap tanks. Pretty sure that by 87, the motorized valves were the standard but who knows what a PO might have done to fix a tank valve issue.

[bennylava]

Originally Posted by Dleslie212

The newer six poet valves need momentary voltage to switch which tank it's drawing from, but then they stay on that tank until switched again.

So they probably sent me the wrong switch, and that's why it wouldn't fit. The simple flip-switch works fine to switch between tanks. When everything is functioning properly, that is. I've replaced the switch, and the selector valve. Both of them got the passenger side tank functioning again, for a while.

Now I guess I have to go after the fuel pump.

[kwmech]

Hatzie has a good write up on these systems along with full diagrams. Depending on the years of your truck, some parts may be obsolete and needing conversion

[hatzie]

1981-1986 CK series DEPRESS FULLY switches are momentary action polarity reversing switches with a center off position. You press to LH or RH and hold til the motor on the Pollack motorized valve moves the shuttle to the selected tank.

The 1987-1991 RV series dual tank switches are ON-ON switches since the TBI fuel pumps get power from the dual tank system. I use these switches on all trucks from 1981-1991. The Pollack motorized valve has always had switches inside to shut off the motor once the valve has moved to the stops.

One of the four male terminals on the switches has a lump to prevent being plugged in backwards. The TBI switches have the lump on a different terminal from the earlier momentary switches.
You can use the 87-91 switch on the 81-86 systems by filing a notch to accommodate the new lump location.

Here's the Theory of operation thread covering all the dual tank systems used on the 1973-1991 squarebody trucks.
https://67-72chevytrucks.com/vboard/...d.php?t=754061

[bennylava]

So to clarify, depress fully is NOT "press and hold"? My 87 uses the simple flip switch, which functions like a light switch in your house.

Side note, I'll definitely make use of that fuel pump test terminal shown in the link. Never knew that was there and will be quite useful.