tail light making me crazy

thanks, folks.
i suspect a ground issue and especially now that i see your feedback. i'll try adding one to the housing and see what happens. btw it's a 65 valiant and yup, got the wire diagram.

i'll report back.

If you go to MyMopar you can also download a full service manual:

http://www.mymopar.com/index.php?pid=31

The 65 Plymouth one is what you want

http://www.mymopar.com/index.php?pid=109