In reply to:
Wait a minute. I just reread your message. You don't have it in your hands yet. I'll bet the Clarion unit has instructions on how to properly wire it. Why don't you just wait until you get the unit, and then read its instructions?
Y'know, that's a good idea.
Seriously, though - I've installed a few other FM modulators, and they've all been close to the same. I didn't think about a ground loop - I should watch for that - but the big question I had was about the amp-power-on. That's exactly the behavior I'd need if the auto-modulator-on is to work at all. Thanks, Tony!