Is the inertia switch there for shutting off power to the relay in the event of an accident?
Yes. It's a backup system in case an engine keeps on running after an accident where they may be a fuel system puncture of failure that causes a leak.
I read through the painless manual and even though not many of the colors seem to match... I think I can figure most of it out.
Match what? Factory Ford?
At least half of the Painless circuits are added and don't necessarily match what you may have had on a Bronco, but some might actually match more modern Ford colors. I don't know that though, so maybe we can ask Eric sometime.
But 99% of the main circuits match the Ford colors you should have had with the original harness. There are some variations, mainly for '66 trucks that had the oddball stuff, and most year's variations in the steering column, but like you said most of that is figurable outable.
The ignition switch wiring colors are not stock unfortunately. Most are "correct in the color department, but not the location. For example the original power wire was Yellow and the original ACC wire (on the back stud) was Black w/green. The Painless has a different orientation. But things should still work.
They just won't always match the factory manuals.
Only thing I need is to find a wire to use for the ign power. Everything is tied up tight and difficult to get to- is there something I can tap into for the acc ign wire? Only green/red wire I got goes to the alternator.
Not sure of your wording. You mean that you're just wanting to find a wire that works in ON only, and not ACC, for use with your pump. Correct?
That's what started this thread, so figure that's what you meant but wanted to be sure.
I'll check the instructions, but pretty sure only the Red w/green and Green w/red wires are in ON only and not ACC. But while I would not tap into the Red w/green unless I had to, I don't see a problem tapping into the Green w/red wire for your alternator regulator as long as you use a relay to actually power the pump.
You just need to make sure that the alternator still gets what it needs. No big load needed there, so it should be able to share with the pump relay.
Paul