To relocate the pmd in my truck i was told i will need a heat sink? Could you tell me what a heat sink is what it does and where i can get one? thanks for helping

A heat sink is usually aluminum, and it serves as piece that dissipates heat generated by an item. They are usually an aluminum plate with fins on it, increasing the surface area. Aluminum is a good choice because it accepts heat very easily as well as dissipates it very easily. A simple heat sink can be had on ebay, at radio shack, or out of an old computer, etc. They are everywhere. You want a fairly large one, that way it ensures that you have adequate heat dissipation. Take a look at this link, it might be helpful.
http://www.dieselplace.com/forum/showthread.php?t=270036

Goto the FAQ section or perform a search. This has been covered a billion times on here. Don't want to be a a$$ but its true.

If you go to mygarage (mine), there is a picture of a PMD mounted on a heatsink just to give ideas on how it looks like.

Personally, if you don't know how to find one, get the one from Heath. It has 7 years warranty, comes complete with an extension cable, heatsink, resistor.

My PMD currently resides on the heat sink of one of these. The Dart didn't want to cooperate with me, even with threats, so it got retired into a PMD heat sink. :D

http://news.thomasnet.com/images/large/2005/05/463453.jpg