Getting my plane ready for Annual (1963 PA24-250). I'm getting to know her better now. I was looking where the main spars connect and there are 2 large cables (approx 3/8") attached to the connector plate that head out towards the wings. I looked it the Parts catalog, but did not see it. Just curiosity, but what is it.

If they go from the center of the fuselage in front of the spar, and then each curves out to a wing, you are looking at the main landing gear push-pull conduits.

William, those are your landing gear conduits.
If they are green / blueish in colour then they are the upgraded conduits and if they are metal
then they are original style. Have your A&P closely check the log book for any replacement of these conduits. If they are original then depending on the size of your wallet have these replaced proactively. The conduits are about 400 dollars a piece and should be replaced by a knowledgable Comanche A&P. Not saying that only they can change them, Its just one of those jobs that can take three times as long doing it the first time.... also the setting of the limits switches are very important to get right. Once again anybody can do it from the service manual, but it must be done right for your gear to be safe.

Good that you are digging in there with the annual, its always good to get extra knowledge of the inner workings of these
birds.

Good Luck,

Gary