Jaydee,
I see that everyone else has probably helped you enough but I just wanted to chime in. I had the exact same problem on my 66. The interior lights and the headlights would pulse depending on engine idle. I was having some other probs at the time so I ended up replacing the alternator (higher amp model) the voltage regulator and checked, cleaned, and rewrapped all the connections I could find - all at the same time. The pulsing hasn't been back since, but now I don't know which of the three "fixes" solved my problem. If you still have troubles it's always good to start with the cheap stuff like the regulator. Hope you figure it out.
Stefan
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66 Tahoe Turquoise Coupe
Laser Red 96GT Ragtop
Both are slow but easy on the eyes!