Here is my problem. For the past couple weeks when I start my 69 camaro my tach will bounce badly and even go as high as 2500 rpms. The motor is still at idle but the tach is acting crazy. During the time it does this my voltage gauge is low, reading approx 11-12 volts. It will take about 3-5 minutes then my voltage will go up to 14 volts. Sometimes it will drop to around 13 volts but when I hit the gas it will climb back up to 14v. I currently have the external regulator and 3 wire alternator. I am thinking about buying the conversion kit and go with the 1 wire alternator.
Does anybody have any suggestions about my problem.
Somebody did tell me I might have a bad engine ground wire.

Bad ground is a possibility, but i would check the Voltage regulator and alternator as well.

I'd look at the grounds, too. Especially the ground wire from the regulator to the rad support. As the reg is rubber mounted, it don't works so wwell without the ground wire.

Also check the neg pigtail from the battery cable to the rad support.