I found this last week when I was considering an MDS light I printed it because it looks very helpful.
This one is for all the guys who've asked me to post a DIY on installing a simple LED to indicate when MDS is activated on 06+ equipped Rams.
I have not personally done this, as I have a non-MDS '04, but had this shown to me by a buddy who did it. Unfortunately, this friend is about 350 miles away and I've been unable to find any "how to" pics. So you'll just have to follow the written directions. This was done on an '08 1500, but I believe everything is the same for all '06+ models.
Basically, you'll need an LED (one with a built in resistor is advisable, otherwise you'll have to wire in a separate resistor. These are readily available at Radio Shack), about 10' or so of about 22 ga. wire, a crimp type wire tap and the various tools needed to crimp, solder, etc. and something to mount the LED to the dash, whether you want to get fancy, or just use a nut type connector and drill a small hole for the LED. You may also have a small panel to pop out that's made for an accessory switch. Again Radio Shack or an auto parts store would have an assortment of items to mount the LED to your dash.
First thing is to find the Brown/Orange strip wire coming from the C3 connector of the PCM located on the fire wall behind the air filter. The top connector is C1 and C4 is the bottom one. Using the wire tap splice in the wire your going to run to this Brown/Orange wire.
You can now run your wire along the side and rear of the engine compartment, using simple tie-wraps to secure it as needed. A convenient place to take it into the cab is through the grommeted hole used for the hood release cable.
Basically, once you have your wire run into the cab, find where you want to mount your LED and drill your hole, pop your panel or whatever and solder your wire to the positive lead coming off the LED. Cut a length of wire for your ground and solder it to the negative side. After mounting the LED, run your ground to a suitable place on the chassis or to where the radio is grounded.
That's it, your done. Piece of cake. Now every time your MDS kicks in, the LED will light up and when it kicks off, the LED will be off.
I was able to find a pic on another forum of a guy who got VERY creative using the cig. lighter hole, a piece of clear plastic, some 1/4" letters and black paint. He basically cut the plastic to fit the lighter hole, put the letters on, painted it black, then removed the letters. Looks great!!!