72 A/C harness questions

[72junky]

Hey, I'm in need of some quick and correct answers to order the right A/C harness for my truck. I have searched the electrical section and have too many other years coming up.

Facts: 72 A/C, TH400 automatic, 350 engine

Questions:

1. Did all '72 trucks come with the "anti-diesel" relay? Is this the vaccum thing next to the choke coil on the intake? It's about the size of a D cell battery with 3 vaccum ports and male plug for wiring. My other trucks have them, but, missing on this truck. However, a bunch of stuff is missing, hacked, etc.

2. There are several different transmission controlled "anti-knock" harnesses shown on AAW site, how do I know if I need one of these too? I've owned over 10 of these truck over the years and have NEVER seen or heard of this. Is this a "California smog" option?

3. Any preference of wire harness companies? American Autowire, M&H, or lectriclimited? I've checked out all three sites, same pricing, same part numbers, but, not quite the same descriptions for the actual harnesses. Are they all the same company? Price fixing? Should I call my congressman? Any forum vendor reccomendations?

Thanks in advance!!!
Brian