I am in the process of putting in a Secret Audio system in my 66. I've got the front speakers taken care of but am having problems finding a good solution for the rear. I am looking for a nice clean look with great sound and hidden wires. Anyone out there have any suggestions?? :cool:

That sounds good. IMO, the best sound system is the one you can't see but hear.

I have to 6x9's behind the curtain with the wire run under the carpet, so nothing is visible. It really completes a nice full sound when working with the dash speakers, i like it a lot. The only bad thing about it is i had to put both speakers on one side since they are in boxes, so i can keep the spare on the other. This works good for me, maybe it will be good for you.

If the speakers you are using are not too large, you can mount them aft of the rear cab wall...underneath the panel at the front of the bed. The 2 rectangular vent openings at the lower outboard corners will work nicely for this. Speaker grille goes on the cab side, and speaker itself goes on the bed side. Wires can run through holes that are already in the corners.
Neat, clean, efficient.

Elkyholic. I installed a speaker wall in the rear of my 3rd gen '72
http://levitanj.home.mindspring.com/elky/restor2/page1/rearspeaker4.jpg

Not sure if it will work in your '66. It was made out of some plywood, a wood fur strip, some black carpet. I installed some Infinity speakers and it sounds great. Plenty of room in back of the wall for amps.

I really like how that speaker wall looks. I would do the same with mine, but don't feel like ditching my spare.

Thanks for the compliment. I use a small "doughnut" spare, and I took it out for the picture. It fits pretty good. I'm going to have a black vinyl cover made for it this spring.