which is the auxiliary tank and which one is the main. I should know this but it escapes my memory right now. Oh and what is the capacity of each? Thank you so much!

 

Just went through this debate a couple of days ago. Aft axle tank is the main, midship tank is auxilliary.
Here's the page from my '73 owner's manual.
Here's a link to the other thread:
https://www.ford-trucks.com/forums/1...l#post12148892

 

Thank you! My husband will think I am so smart but I will give you the credit!

 

Happy to help. The main tank is 19.5 gallons, the auxilliary is around 20 gallons, I'm not sure of the exact capacity.

 

Ah yes the debate...

To answer your question about capacity, to be more accurate we need to know the year, the Model, If it's 4x4 or crew cab, or a super camper special, or if it's got evaporative emissions.

Too many variations in capacity between the trucks, as they can fluctuate as little as .1 of a gallon to several gallons between models.