Fab your own Serial Cable:
Pulling up this old thread, since still the main discussion of Holley Commander 950. From other threads, looks like OP 67Dart273 upgraded to the later Holley HP ECU. Finally have time to fool with my Commander 950 stuff. One came w/o the serial cable, now "not avail" on Holley's site, so I had to make my own. I pinned out the Holley cable I have. The mating round plastic 4-pin connector is AMP PN 206060-1 (CPC Series 1, Size 11). Insure you also buy female pins and the cable clamp. If procuring both sides, you could use any convenient 3 or 4-pin connector (even USB). Use a DB9 female molded cable long enough to reach your PC and cut the other end off to install the AMP connector above. Below is the pinout to make your own cable (use commas to align columns):
ECU pin, Function, Round_male, Round_female, DB9 (PC end), PC function
A12, Serial Gnd, 1, 1, 5, GND
A9, TxD, 2, 2, 2, Rx_Out
A8, RxD, 3, 3, 3, Tx_In
A2, ModA, 4, none,,
A3, ModB, 4, none,,
A2 & A3 must be connected together, even though they don't continue on the serial cable. You can do that anywhere. Holley simply used pin 4 as a manufacturing convenience.
You need to plug into an RS-232 serial port on an old PC, or use a USB-serial adapter (DB9 connector). You must assign your PC's serial port to the same com# which the Holley ECU is using. When you can communicate, you will see a version# for the ECU in the About box of the Holley PC program. You won't know which com# the ECU was left in, so might need to try com1 thru com4. Change on the PC side in Device Manager. Right-click adapter (under ports) - Properties - Advanced and should get a box to set com#. Varies with adapters and your Windows version. I used a Win Vista laptop. I'll later try on a Win10 PC.
