Dash Light/Taillight Problem

[74747474]

This is a problem I'm having w/my 73 Cadillac. I figured that all the GM vehicles are wired the same way, so I hope you guys can help me. I keep blowing the fuze that controls the dash, tail and parking lights. I'll replace the fuze, start the car up, and all the lights will work fine. If I start to drive it though, at some point in my journey, the fuze will blow. Sometimes it happens pretty quickly w/in a couple of minutes, sometimes it takes longer, about 20 minutes or so. It's really unpredictable. Again, if car sits, fuze is good. The fuze only blows when the car is moving. The book calls for a 4 amp fuze, and I have used fuzes up to 8 Amps, and the result is the same, again with the same unpredictability of how long it lasts before the fuze blows. This is driving me crazy....help.