There's an adapter that drops speaker level outputs to the level the Bose amp needs. Pre-outs don't provide enough of a signal even at 4V or 5V.

The W140 has 4 6.5" woofers in the rear deck, a full range in each rear doors, mid and high separates in each front door and a center channel by the rearview mirror. Dash speakers are for the phone.

Sixto
93 300SD