12 to 6v regulator 15a?

Working on converting a old truck from 6V to 12V.
I dont know what the amperage draw is from the blower motor. The truck is at a remote location. so I was looking at designing a regulated supply capable of providing at most 15A at 6V.
Having a hard time locating a schematic that uses common regulators I have in stock, that are capable of that high current rating.
I envision three separate circuits, 2 5A circuits with one 15A. I will fuse them and have an LED before the fuse to indicate a intact fuse.
Not alot on this truck thats needed. Should cover everything.
I am not real familar with paralleling regulators, but is it possible to use multiple 317's to accomplish this?
Does anyone have a schematic handy for this? Or references I can look at to lead me in the right path?
Thanks!

You mean a LED across or AFTER the fuse to show it's intact?

2N3055s etc are used to beef up regulator outputs. You should find circuits via google etc, typically with a 0.1 Ohm resistor on each 3055 output to force current sharing.
But I think that's overkill, plus it's 120W of 3055 heat to dissipate (must not touch GND or +12V). For a fan (especially if single speed) a 100W 0.5 Ohm (for 15A; 0.7R for 10A etc) should do.

If going the regulated route I'd consider the newer switched-mode regulators (dc-dc converters). They are typically well over 80% efficient, often 95% etc (hence under 20W heat 80% @ 15A), though it may be trickier finding something 15A capable (maybe a modified Current Logic 12V/24V to 5V, Step-down, 20A, 100W?

For low currents (2A, 3A etc) there are various cheapish "step-down" modules based on the LM2576, LM2577 etc, or see Current Logic.