Auxiliary Fuel Tanks in a C-20

[Happy_dan]

Greeting all. I was lucky enough with the help of a member here to have recently purchased a 68 C-20.

I don't see anything on the SPID about aux fuel tanks but there are two tanks extra tanks in the truck. They are installed in front of the rear wheels and fill from the rear wheel wells.

Are these original equipment or added after the sale?
There is a switch by the drivers seat that I assume is to switch between tanks. I don't plan on ever filling the tanks since the amount I will drive it will never use all that fuel.

When you switch tanks does the fuel gauge switch too?
There is some wiring under the bed (see picture) that I wonder if it was for adding a gauge?

Any information about these would be much appreciated. The truck is awesome. Just waiting on carb rebuidl kit so I can get it running right.

Happy to join the fray!

Lots of pictures here:
http://imageevent.com/happy_dan/dantoys/68c20

[Stocker]

Those are aftermarket tanks. My K20 has aftermarket saddle tanks (Travel Tanks, no longer in business). Mine fill through doors in the bedsides. Your selector appears same as mine and does not switch the gauge; I have a 3-way electrical switch at the bottom of the dash for the gauge. No clue about the wiring pic, have you tried tracing the wires to see where they go?

[Happy_dan]

I have not traced the wires just yet. Just got the truck Friday and changed the oil and pulled the carb. I will get back to that later.

I will change all fluids, plugs, wires, cap, points, condensor, cap etc over the winter but for now I am just trying to get the carb done so I can drive it!

Thanks for the info, I figured it was aftermarket but I think installed a very long time ago.

Now, where did I put my timing light and dwell meter?

[bigdog55]

I have a GMC that I added the aftermarket tanks (I found them at a swap meet). Since my truck came with leaf springs, the saddle tanks are made a little differently than the Chevy saddle tanks,I found out the hard way,

[Barnfind46]

I remember Dad's truck having saddle tanks. There were no senders in the saddles so he would run off of them first. That way he knew he had gas in the factory tank to get home in.

[jocko]

Originally Posted by Happy_dan

Greeting all. I was lucky enough with the help of a member here to have recently purchased a 68 C-20.

I don't see anything on the SPID about aux fuel tanks but there are two tanks extra tanks in the truck. They are installed in front of the rear wheels and fill from the rear wheel wells.

Are these original equipment or added after the sale?
There is a switch by the drivers seat that I assume is to switch between tanks. I don't plan on ever filling the tanks since the amount I will drive it will never use all that fuel.

When you switch tanks does the fuel gauge switch too?
There is some wiring under the bed (see picture) that I wonder if it was for adding a gauge?

Any information about these would be much appreciated. The truck is awesome. Just waiting on carb rebuidl kit so I can get it running right.

The floor switch is purely mechanical and only selects which tank to use as the feed tank to the fuel pump.

GM's RPO NL2 did have a round dash switch that would select which tank's fuel quantity was displayed on the gauge (same shape as windshield wiper and light switch) on the left side metal of the dash - just above the a/c outlet (if you have a/c), but that area. It was totally independent of the floor switch.

As Stocker mentioned, saddle tanks were an aftermarket item. Back in the day, most didn't have switchable senders in the tanks, when you started to chug-a-lug, you switch the floor switch to a fuller tank and hoped for the best.. BUT, some saddle tank mfgrs did offer senders and gauge switch panels. One can be fabbed up using just a toggle as Stocker mentioned as long as you have senders in your tanks - but the selection of fuel gauge input is totally independent of which tank you have selected as the feed tank for the fuel pump. Gives you the freedom to check all your tanks by the flip of a switch without actually changing the current feed tank selection. Below are some pics for reference. 1st two pics are the GM RPO NL2 option that was offered by the factory (this is NOT what you have). Beyond that are some original period fuel gauge sender switches for reference. Last pic is how MY tanks were oriented on the floor switch - note every truck can be different. Your fender fill tanks are my favorite kind, stealthy!

Only way to know if your wiring is for a fuel sender is to find where it comes from. Basically you need a little extendable mirror and a flashlight so you can peek on top of the tanks and see if there is a sender/wiring. If not, then you'd need to source senders, wiring, etc or just leave it old school, gas is gas even if you can't read it on a gauge - and just do it like barnfind mentioned, that way you'll know you always have at least what your gauge shows.

[jocko]

some saddle wiring info. Last pic is the bezel that goes around your floor switch - if you install this, ya gotta pay attention to how your lines are routed!

[Stocker]

Thanks for those posts, jocko -- great info, very informative. Other than my gauge switch being at the bottom of the dash, it appears to be the same as in your pic, right down to the "Travel Tanks" sticker.

[special-K]

It would help if we identified that handle on the floor as controlling the "valve" and not a "switch". It is a plumbing item, not electrical. Then comes the switch if so equipped. "Tank selector" is what it is. I've had the '69 and the '72 factory option tanks but also aftermarket. My '72 GMC has a pair in it. I think those are Leisure Products brand. All the aftermarket tanks I've had in trucks have been set up with a gauge switch. I believe that was part of the kit, so when installed professionally they would have that switch

[Happy_dan]

This is great information. I am totally enjoying learning about this truck and so happy to be part of the hobby. I am quite knowledgeable about Camaro's but not so much the older trucks.

Now to see how well I do at rebuilding the quadrajet.

[vitamin_c95]

Yeah, that floor switch is really nust a valve.. if your lucky you have senders, I have a feeling you don't. My 71 didn't.
Take a straight on shot of that connector and post for us

[Happy_dan]

Thanks! I will get a straight on shot of that plug (I am a ham radio operator and it reminds me of a mike plug, I think it was 4 pins).

I will get the carb rebuilt and back on the truck, then get it back on the lift, remove the cover that protects the gas tanks valve and trace the wires too. I am curious about that one for sure. I can see the trailer brake controller wire but no clue what that one is.

I am not even sure how to operate that vintage trailer brake controller! Looks like you have to slide the handle along to operate the trailer brakes.

[JustToxic]

The wiring harness you have pictured is to plug into a camper that fits into the bed so the camper lights will light up. Looks just like the one I pulled off the '71. If you follow it back up to the firewall you'll see it is a T plug that plugs into the rear light connector. My step dad's '71 had a taillight issue and was able to track it back to that harness shorting to ground, due to it just hanging under the truck.

[vitamin_c95]

Yeah that's what I was thinking. I was gonna say for a 5th wheel. Wanted to see end first

[Happy_dan]

Well, hopefully I'll get the carb done and the truck running this weekend. If so, I will get it back on the lift and do some investigation. More to come.

[Happy_dan]

Well, I did get the carb done and it was running great..... until it wasn't. LOL. Stranded me down the road a piece. I have driven it several times and it seemed fine, but then started to stumble and quit. Pulled the air cleaner and gas everywhere. Time to pull the carb again. Might be time to get a new one.

Anyway, that is not the reason for the post. I was not able to trace the wires because they go above the cover where the fuel lines go. I was under the truck looking for something else and remembered to take pictures of the plugs. They have been there a long time. I had to laugh seeing tied up with string.

Here are the plugs that are just sitting under there.