[70oldgoat]

1970 GTO

A new, reproduction remote outside mirror was installed (driver's door). It won't work.

I believe the cable is too long which will not allow one to adjust the mirror from the inside (too much cable tension on the mirror).

Is there a way I can modify the cable? I don't want to return the product if I can fix it..

[1970GPJ400]

The cable length shouldn't be an issue as long as it's not kinked. Did mirror operate properly prior to installation? If so I'd try securing cable inside door in a loop fashion to minimize possible kinks. I installed an aftermarket mirror in my 70 GP and had issues with the cable end operating lever not securing to my original bezel. Had to secure it with a set screw tapped through the bezel.
I would not attempt to shorten the cable - the odds of successfully doing that are very low. Cable wires are crimped at the factory in the weak pot metal - try to open the tabs to release the cables and they'll break.

[Toms bird]

I would make sure it's not kinked. Oil the wire inside the sheathing. Make sure the part that locks into the door is secure. If that set screw needs a little help put a piece of copper on opposite side of screw in that housing to take up some slack. Also if you push the mirror by hand from the outside will the inside move..

[First Bird]

I also had to tap a new, slightly larger screw to attach to the bezel. After install, the repro mirror vibrated in the wind. Couldn't see nuthin. The cables were just a little loose. Every method I thought of to shorten the cables would probably destroy the unit.
What ended up helping was putting a minor twist in the cable before securing it to the bezel.