Interior lights pulsing???

[Jaydee]

I have a 65 K code coupe which has had this problem for a while. At idle, all of the interior lights including the dash and radio lights have a continuous bright/dim, bright/dim pulsing effect. Once driving at normal speed, this condition disapears. All of the interior wiring is still original but looks to be in very good shape with no splices. I have replaced the altenator, alternator harness and the engine to firewall ground strap which did not make a difference and I can't see anything else thats looks out of place. Any ideas??