Re: 1970 Factory Auxiliary Tank
 

I'm not sure about 1970 but I bought several C10 trucks new and ordered them with an auxiliary tank. All were step side beds.

Later (1979 or so) had a rocker switch on the dash to toggle between tanks. It operated a solenoid valve and also switched to the other sending unit.

I was buying a new truck every year at the time so I don't recall which one did what but one year changed from a simple solenoid valve to motor driven worm screw valve. Instead of just toggling like on/off you had to depress the switch and hold it while the valve screwed open or closed. I didn't read the manual until I was stranded because the tank didn't switch.

Re: 1970 Factory Auxiliary Tank
 

Here are some more pics of the N18 1970-only aux tank option from other trucks I thought I'd add to this thread.

Re: 1970 Factory Auxiliary Tank
 

Unlike the 71/72 aux tank, the 70 version made use of a metal bar - one end extended up into the cab and allowed the driver to select either tank; the other end was attached to the valve itself (as shown above). The bar removed from the truck can be seen below. In the 71/72 version the bar was gone and the valve had a selector that extended up into the cab LH side.

Other pics show the fuel neck components:

Re: 1970 Factory Auxiliary Tank
 

This option made use of the Blazer tank, which will contact one of the overlying bed supports once in place. Some of you guys who have done the rear tank swap have notched this support. Here's what Krazyray told me about about how GM dealt with this issue:

"The tall bed support that gets in the way of the rear tank was not on that bed. The factory instead installed a short bed support...the same support that is in front of the wheel tubs. They used shims to make up the height difference to the frame. That's probably why it worked with no extra mods."

Re: 1970 Factory Auxiliary Tank
 

Deadhead I think the tank in pics was actually like the 60-66 Suburban. Has the curved area for spare tire.

Re: 1970 Factory Auxiliary Tank
 

Thanks - good eye.