Hi everyone! Right off the bat here...YES I'm a newbie....Late in Life finally getting a Diesel to learn and grow old with!

I feel I've been very lucky to find a 1998 12 valve Truck in showroom condition! Not even 100K on motor and frame is spotless! The truck
was "modified" right out of the factory...someone wanted a "show truck" and put a ton of things into the truck... 4 air bags, messed with the rear leaf
and shackles (found them split/cracked) and did all kinds of messy splices into the wires and such...

I've had the fun of redoing the whole front end- came out great! Also did the rear with proper factory springs and such and got rid of the 4 air bags...
so I guess it's back to being a "man's" truck?

I also did an awesome job with fixing the wire mess in the rear, did a really nice neat job of it all. Here is my SNAG! help!? yes..please help!?

I came across a switch with a round red bulb along side of it. Like I did with the other 50 some wires...I traced them "to and from" to know and understand
where and why they went where they did. Well...I traced this one and I'm NOT IMPRESSED!??

With idea's from others, I think it's the TC LSwitch...but here's the odd way it was done...a thin crappy wire was pushed under a fuse in the fuse panel for what I feel is to be power? That ran to this round red diode(never lights up)...it then came out of that with even a thinner wire to the switch...then from the switch it went out the cab under the hood and all the way to the PCM and the other wire in the switch went to a good ground. After dealing with all the other wires "jerry rigged" in the back of the truck for lights and such...This TC L Switch set up does not look so healthy either. When I drove the truck home after buying it, I've felt that at higher speeds it could have used an Over Drive gear...like it was just in a 3rd gear..?? I asked the previous owner about the switch and if anything special I needed to done when using or driving the truck...he had no clue as he was the second owner(very short time) and didn't touch or use any switches...

Sorry for the long talk...but felt a little history needed. My question is...before I use this truck every day...what do I need to do? I feel this current switch is NOT the right or safe way to use it for it's intentions? How and what do I need to look at and study...to find out the TRUE and right way to set this truck up!? Is this switch a poor mans way? Someone tryin' to save from buyin' a proper kit or such to set this up right? What else did they mess with...that I should know about?
Thanks in advance for any help...and your patience with me the Newbie!