What modifications (custom or factory options) have you made to your C3?

For bonus points, post a picture of your change(s)!

I hated having the charger for my phone poking up out of the ashtray door, but I also didn't want to cut holes in the dash for a more permanent mount. One day I happened to drop my charging cable on the console and the end randomly landed in the "coin tray" behind the power window switches. The light bulb went on... 

Wow! I absolutely love this!!  How are you sourcing the power for these ports?

MSD distributor and 6A spark box.

DeWitts aluminum radiator.

Replaced the old factory 780 Holley for a new Holley 670 Street Avenger carb.

Biggest modification was rebuilding the original L48 block.  Only parts reused were the block, crank and original Quadrajet carb (rebuilt by shop).  Eldebrock aluminum heads, Comp Cams 268H cam, Harland roller rockers, Speed Pro pistons, Eldebrock 2101 intake, Accel blueprint distributor with Super coil, Cloyes true double-roller timing chain, Flotech ceramic-coated headers and ARP fasteners. 

Entire suspension rebuilt with poly bushings, Bilstein HD shocks, HD fiberglass rear spring and Wilwood calipers with slotted/cross-drilled rotors.

Engine just before installation back into engine bay: 

Power is coming from the 20a circuit that powers the lighter. I used that because if i blow the fuse, I don't lose anything critical.
I found a cheap inline 2a charge module to convert 12v to 5v, and then used a desktop PC dual USB port that I chopped up as the external connector you see in the picture: 

2 Port USB 3.0 Cable Type A Extension Code Male to Female

It all just barely fits up under there between the window switches. The hardest part was trying to cut nice rectangles with a Dremel. Those console parts are pricey!

MODS? Not much you can see, but some you can not see. Just up grades and improvements. Try to stay as close to O.E.M. as possible, but NOT N.C.R.S. quality..

That's a super addition - we need a "tutorial" on how you did that!😄

Edit - Ooops, I see you detailed it!  Hmmm, might beyond this "bear of little brain"!😄

I can't pretend to be a "master mechanic" or anything, so limited changes to our old girl over the years. 

But, in the first month of ownership I had to re-configure the lights - stock red indicators are illegal in the UK (and here in France), so it's a fairly standard procedure to use the back up lamps as turn signals and separate the brake lights from the turn signals etc.  I added additional concealed back-up lamps but now I understand it's possible to use switch-back LEDs .  And, I had to add side lamps in the front - yellow side lights are also not allowed.

But we did put a composite rear spring on it in about 1998 - probably the best thing we ever did!   

I added a switch for the hood lamp and put cabling, antenna bracket etc in place for a CB (a removable separately mounted one).  We don't use the CB now, but everything is still there!   

And a double power outlet to make life easier for running a GPS (sat nav) and camera, run from the existing cigar lighter power, with an additional fuse and a switch in the glovebox.....

I rebuilt engine and transmission at 135,000 miles. I have added the '78 pace car spoiler to aid airflow, aluminum radiator and water pump, twin electric fans, and composite rear spring. Otherwise my '69 is the same as I received from the dealer new.