I have my MSD using the coil + wire as ignition switched, as per the MSD interface harness. The coil - goes to the MSD white/points wire.

Can I put a relay on this + wire to make an easy tap for underhood ignition on? Or would that draw too much current and upset the PCM? I figure a relay pulls 150 mA max and the coil had to pul more than that, but...

The PCM grounds the coil to fire Magnet. The + side is always hot via the ASD relay so whatever you hook the relay to will switch via the ASD relay being energized, not the ignition switch.

The O2 downstream heater relay is hooked up on the same + wire via fuse "U" in the PDC.

It will not affect the PCM at all regardless.

Thabks Dan. I new it would be oobvious but I've got 500,090 things going on right now.

I'm looking for a spot to tap my electric water pump drive to. Figured that would be the easiest spot since I already have it broken out to a workable wire.

So when exactly is the ASD relay energized? I know the "duh" ansswer is "anytime the fuel pump is on", but is that only in run, or also acc, or ?

Just in RUN (ON) or

From the FSM:

The ASD relay will be shut–down, meaning the 12–volt power supply to the ASD relay will be de-activated by the PCM if:
*the ignition key is left in the ON position. This is if the engine has not been running for approximately 1.8 seconds.
* there is a crankshaft position sensor signal to the PCM that is lower than pre-determined values.

alright. Looks like I'm going to be having me some electrical fun. Mostly because of that first bulletpoint. I could just tap my dash switch over, but not sure I'd want the fuel pump and O2 heater on just b/c I want the fan and WP on. Guess i get to figure out where to insert a diode in my wiring system.