Carbs with one electric plug on the top of the air horn are for the purpose of controlling a temperature controlled accelerator pump shot (there is NO computer involved with this). When engine is cold, it gives a full pump shot. When coolant temp is high, the solenoid pops out, and blocks off a portion of the accelerator pump volume.
Best example I can find is in an ebay auction...
http://cgi.ebay.com/ebaymotors/ROCHE...Q5fAccessories
The other arrangement has 2 electronic plugs... one in the same spot on the top of the air horn (looks similar, but it's a completely different function...), and a second plug over on the throttle linkage side, down close to the idle mixture screws. These carbs are the CCC version, that use a TPS sensor, a computer, and an electronic metering rod system that raises and lowers the metering rods from signals from the TPS and the computer. I can only imagine these can be converted to use a conventional vacuum controlled power piston assembly, but I've never tried.
Here's a pic of one that requires a computer
