ELECTRICAL DRAIN

I have a 1969 Plymouth Sport Satellite Convertible with the 318, automatic tranny, & A/C. I recently had the motor rebuilt by a reputable shop in San Diego, so everything under the hood is brand spanking new. When the work was done, the car was shipped to Orlando, FL where I recently moved. When driving at night, the voltmeter would run at 14 volts and then for no apparent reason, it would drop to 8 volts & the lights would go dim. Then in a minute it would bounce back up to 14 volts and the lights get bright again. I was finding I had to leave a trickle charge on it if I didn't use the car daily otherwise the battery would die. I removed the negative battery cable from the battery and hooked up a test light to the negative battery post with the other end to the negative battery cable. The test light will glow fairly bright, but then immediately go dim, and then go out. If it tested it again right away it would not light. If I wait a few minutes it would glow and extinguish as before. I disconnected the alternator leads and the drain remains. I remove all fuses one by one and the light test exhibits the same results. I pull the top middle and lower plugs off the wiring harness bulkhead connector and the light still lights. Now start removing and replacing the fuses one by one until the light goes out. I am perplexed and frustrated. Any suggestions? I believe this fix is beyond my capabilities. If I can't correct it myself, what type of shop should I bring it to? Thanx for your time and help! - Tom