Strange, turn on engine, sub = no sound

This is really strange. I just hooked up a new Infinity Basslink II module into the car. I'm using speaker level inputs tapped to the input stage of the car's main amplifier. I am taking the inputs from all four corners. Power + was pulled from the battery up front using 8 gauge cable, a fuse is installed at about 5 inches from the battery post. The total run is 17 feet. The ground is about 24 inches and I installed that by scraping paint inside the trunk area, drilling a hole and attaching the far end with a proper circular end crip-on with a screw.

All in all, this looks like a pristine installation, all wires are neatly tied and routed etc etc... This is about the 8th install I've done (I'm not a pro, but an advanced hobbyist). my previous installs were more of the two amp, 12 speakers variety, but this car I needd to save a few bucks.

So on to the problem, when the car is off, the basslink plays great. In fact, it sounds pretty darn good too. when I turn on the engine, the sound from the basslink stops. The power light on the basslink is still on, but nothing is coming out. When i kill the engine, the sound doesn't resume. It takes a moment.

Seems to me that the amp is going into protect mode. I know it's not the unit because I've swapped out the basslink once already. I thought it may be an issue with taking input via parallel connections to the wires (thereby dropping the lousy low impedence even lower), so rather than tapping the speaker lines, I tapped at the input into the amp stage, that didn't fix anything. Then I thought it was an issue with the automagical sound sensing turn-on, so I ran a wire to car's amp turn on lead, and turned off auto on.

The basslink amp turns on and stays on but sound stops. The device is cool to the touch and shuts down almost immediately after turning the engine on.

what can I try next?

Thanks all!

Peet

ok, basslink on, car on or off... using line inputs sub keeps running. Using speaker inputs it shuts off as soon as the car starts. I tried cutting the speaker grounds one at a time in case there was a common amp ground that caused this issue. I'll prolly get a line level converter to fix this, but for posterity and other's woes, here's some additional info..

Voltage, car off, across posts of battery and across posts on basslink (same): 12.66v

Resistance on ground, measured from end of whip (that terminates at the basslink) to the negative battery post: 0.016 k ohm.

All numbers seem well within spec. All measured with a Fluke 88.

Peet

Yep, line level converter on board, problem gone.

So what's the story? Too much current on the speaker level inputs? (the speakers are 2ohm), or something else?

Wasted lots of time chasing this. Hopefully this will all help someone else down the road.

Cheers all.

For future readers of this post, Infinity suggested that the Bose amp on board that I was tapping off of had a common ground. This caused a ground loop condition to which the Basslink reacted by muting.

Cheers all.