I am not associated with this seller, but I think his product is good. Here is part of my email correspondence from when I bought his 12 pin Gentex mirror cable. $50 seems like a lot but it saved me a bunch of time.
"Our harnesses for the GHSHL4 mirrors include the mirror-to-vehicle jumper harness (12 pin to 3 pin), plus an RCA cable and camera power and ground wires.* The RCA cable & power/ground wires are all part of the harness and are long enough to reach the bottom of the dash (approx. 9 feet long).* That way, once you install your camera you'll just bring the camera video cable & power/ground wires to the under-dash area of your vehicle and then plug the camera's video cable into the RCA female cable on the mirror harness & splice the camera power & ground wires to the power & ground wires on the mirror harness.* That way you are not tapping into any of the vehicle's wiring at all, and all of your connections are inside of your vehicle away from dirt & moisture.
Picture of the kit is attached.
Cost of the adapter harness & installation hardware is $59. If you do not need the wire cover shown in the picture, take $10 off the total (if you do happen to need the wire cover, check your mirror's mounting bracket as the GHSHL4 mirrors came with two styles, one which is a regular wedge mount and the other with an extended mount that is still a wedge mount, but there's provisions to mount a connector on the mount.* If yours is the regular one, the wire cover will work; if yours has the extended mount, then the cover will not work - sample pix of mirrors with the standard mount and extended mount are attached).* Prices include shipping & insurance.
Thank you & have a blessed day!
Best Regards,
Bob Prim
Bob's Automotive Mirrors & More LLC
7697 Forest Lawn Road
Three Oaks, MI 49128-9558
219-575-9220
Philippians 4:13
http://www.bobsmirrors.com
http://stores.ebay.com/bobsautomotiverearviewmirrors
http://www.facebook.com/bobsmirrors
twitter.com/Bobs_Mirrors"
I also was able to find the connector part # for the 12 pin connector, in case you wanted to make your own.
TE part #: 1318774-2 (and then file down a couple plastic fins and it will plug right in). Of course, you'll also need crimp contacts, crimper, wire, etc. The gentex 12 pin pinout is out there on the web somewhere.