Why does the voltage drop suddenly then just as suddenly jump back up to 14

Yes. It does have 2 cables to the positive terminal. I noticed that the cable that runs from the battery to the jump start lead, I believe this is at the ecu/fuse box.... the plastic mount is cracked that holds the positive jumper lead. The connection looks good & clean with the cable, post & metal that comes from the control/fuse box but the mount is definately cracked

Remove, clean and tighten ALL connections no matter how they look! Common problem with this set up. Remove neg. cable first, install it last.

No good. Every connection from battery to starter to engine block ground to alternator has been disconnected, cleaned & reconnected. Car started fine but still has the fluctuating sudden voltage drop the back to normal then drop again. I had the alternator load tested & it apparently was fine, however...just now, I discovered that when the voltage is at 14 & no check gage light on, I can disconnect the battery & car still runs. Next I reconnected the battery, waited for the voltage drop, disconnected battery & car died. Isn't that a classic bad alternator test. Can the alternator work intermittently like that ?