I bought the "Y" adapter for under seat connection to the accessory circuit. Pin out is a little confusing. On my first try, What I thought was a "-" caused the computer to read an error. Switched to using frame for ground and it works OK.
The Accessory plug can be confusing. All four pins are active, one of which is the negative post.
1. Is + when you turn the ignition on
2. Is + only when you turn the Accessory switch on with the ignition on. (Switched)
3. Is the Negative
4. is a positive lead from the brake light when the brake is applied.
I have my GPS connected to the switched lead on one section of the "Y" connector and the other section is used for my Wig Wag module for my brake lights. Very handy circuit.
I had to use a volt meter and the manual to sort it all out.