First off, I own a 2004 S2000 with a factory radio.

I'm trying to connect an FM Modulator to the factory radio. Everything else is really straight forward (Antenna into FM Modulator, FM Modulator into Radio Antenna connector, RCA to 1/8" jack to MP3) except . . .

the power. I figured I would connect the power (red cable) to a red cable on the back of the wiring harness (there are two, I tried the big one first, then the smaller one) and the ground cable (black) to a black cable on the wiring harness. I'm using small 18-22 gauge wire tap-in connectors to make the connection, but I couldn't get either connection to work.

Does anyone have a wiring harness diagram and/or advice on where I should be connecting the power and ground cables?

Thanks in advance,
David