Use flashlight, and look inside the framerail from front and rear of the fuel tank, you should see almost the whole line. Other than that, only way to be sure is to drop the tank.

 

It uses power steering fluid instead of vacuum to apply the brakes. The diesels use them. I upgraded and it's amazing. It's kind of pricey though but worth it if you want better brakes. I would check the rear line and cylinders (although you didn't lose any fluid). If those check good, it's more than likely your master cylinder

 

Not uncommon for the master cylinder seal to go, dumping fluid into the booster, so you don’t actually see a leak, but go through fluid in the reservoir.

Brake fluid will ultimately ruin the the booster diaphragm.
If get to it in reasonable time and wipe it all out, you can save the booster.

 

I don't think the abs/brake lights would come on if it was the master cylinder. I have two rams and blew out the same line twice on one and once on the other. Both did exactly what you described. The fluid in the mc will travel between the front and back until it gets to a certain level. Then it will drop when it leaks out. Try holding pressure on the pedal and see if it drops. If so have a look at the frame(inside) next to the tank. It shouldn't be hard to find if that's your issue.

 

Do I have to remove the booster in order to wipe it out?

 

If the line is my issue, is it a big job to change? Sounds like I'd probably have to drop the fuel tank, no?

 

You could fish it behind the tank

 

When mine broke, I just bought a long length of line, stuffed it down the frame rail behind the tank, hooked up the forward end of the line, then bent the rear part around to where I needed it, and hooked it up. It ain't fun, but, it works.

 

My first break was near the front of the tank and the second was in the back. Both times i did the repair with out dropping the tank but really depends on where your break is. Another issue i found was at the local auto parts store the universal lines they sell the rear oem fitting (into the hose) is longer than what's on the universal tubes. The short ones won't seat so you need the long one. Then you have to see if they sell one separate or use the oem one. Another option if you plan on keeping your truck is get 304 stainless lines from ss tubes I have a full set just haven't gotten around to putting them on.

 

I used SS Tubes, love them