Why Do Single-Tank Trucks Need A Tank Switch?

[Gary Lewis]

I found something in the catalog today that has me puzzled, so perhaps y'all can explain it to me.

As you can see below, the catalog says that 1980 - 86 trucks with a "single fuel system" take tank selector switch D5TZ 9A050-A, which is marked D5TB 9A050-AA and has 5 terminals.  I just so happen to have one of those rascals and can tell you that it takes a different connector than all of the other tank selector switches, which have a 6-pin layout.  (By the way, I have a page up that shows the various switches used on these trucks: Fuel Systems/Fuel System Wiring.)

I've gone to the EVTM's and am now even more confused.  The 1981, 1884, and 1984 EVTM's show a 5-pin terminal that can only fit the D5TZ 9A050-A, and it isn't until the 1986 EVTM that the 6-pin layout appears. However, the catalog shows that a 6-pin format was used as early as '83.

But none of the EVTM's show a switch on single-tank trucks, only show a switch for trucks with dual tanks.

What am I missing?  Why do trucks with only one tank need a switch?  And, did they have one?  Any of y'all have a single-tank truck?  Does it have a switch?

Or, does "single fuel system" mean that they only run on a single fuel and not, say, gasoline and LPG?

[85lebaront2]

Very likely, Ford and and Chrysler were all offering LP gas options for trucks. We had a father in our scout troop who would loan us a GMC pickup with the 305 V6 and 4 speed Hydra-Matic that ran on LP gas.

[reamer]

No tank switch on my single-tank flareside...

[FuzzFace2]

reamer wrote

No tank switch on my single-tank flareside...

Same here on my 81 F100 single-tank flare side.............till I added the 2nd rear tank
Dave ----

[Gary Lewis]

I think "single fuel" must not mean "tank" and instead means it wasn't set up for more than one fuel.

[Dyn Blin]

Hey Fuzz, do you have a write up on your 2nd tank addition somewhere?  

Thanks