From the batlab forums
"From the HT 750 Basic Service Manual....
1. Turn source and target radios off.
2. Connect cloning cable to side connector of both radios.
3. Turn on target radio.
4. On source radio, simultaneously press side buttons 1 and 2(the one above the PTT and the top one below), then turn radio on. Both radios produce a "clone entry" tone, and turn on their green LEDs.
5. Release both side buttons. The transfer process begins and may take one to three minutes.
6. When cloning is completed, both radios reset themselves and turn their green LEDs off.
7. Turn both radios off.
8. Disconnect the cloning cable and turn the radios back on for normal operation.
Note: Cloning can be performed only on radios with identical model numbers and software options."