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Calling all Motor heads to check and see if you ever installed or own (ed) a car with an old Holley Commander 950 EFI system. I am looking for the computer to ecu connection cable which is now unavailable and seemingly impossible to find. I need this cable to set the parameters of the EFI system on my newest car. The Holley part number is 534-140. If you have one or know of someone that does please contact me. There has to be 1000's of them laying around in the bottom of the box the kit came in or in a drawer of a tool box. Thanks in advance. Jim Vickers 812-972-4516 sales@federalknife.com

Holley Commander data cable

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  • Holley Commander data cable
Last edited by Jimmy V.
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I'm a ham, and run into this all the time. USB to DB9 male serial adapters are available. This will get you halfway.

Do your research. I can't remember if it was Prolific who changed their adapter firmware. If you have an old one it simply stops working when Windows 10 updates the drivers. I just went through this(very frustrating and futile) and bought a new adapter to use with my Megajolt3 which uses a DB9 serial port. Serial ports are gone, USB is on it's way out(being replaced by USB-C) and ethernet ports are disappearing too. Wireless WiFi and Bluetooth are ever prevalent.

I bought a new FTDI adapter on Amazon for about $10.

https://www.amazon.com/gp/prod...00?ie=UTF8&psc=1

For the other half, I would use Greg's pinout diagram and make one, but that's just me.

I've got a few male-female serial extensions laying around, need one Jimmy? I'll throw it in the mail for you free. It looks like you only need TX, RX, and ground, so 3 out of the 4 pins on the round connector.

Last edited by DannyP
@DannyP posted:

Do your research. I can't remember if it was Prolific who changed their adapter firmware. If you have an old one it simply stops working when Windows 10 updates the drivers. I just went through this(very frustrating and futile) and bought a new adapter to use with my Megajolt3 which uses a DB9 serial port. Serial ports are gone, USB is on it's way out(being replaced by USB-C) and ethernet ports are disappearing too. Wireless WiFi and Bluetooth are ever prevalent.

I bought a new FTDI adapter on Amazon for about $10.

https://www.amazon.com/gp/prod...00?ie=UTF8&psc=1

For the other half, I would use Greg's pinout diagram and make one, but that's just me.

I've got a few male-female serial extensions laying around, need one Jimmy? I'll throw it in the mail for you free. It looks like you only need TX, RX, and ground, so 3 out of the 4 pins on the round connector.

Prolific rewrote their drivers so they wouldn't work with pirated chipsets. Genuine Prolific hardware wasn't affected. While I can't blame them, it backfired because angry customers flocked to FTDI.

I built my own connection cable using an old 9 pin computer cord and cutting one end off exposing the wires and isolating the 3 wires the system uses . I used a diagram from one of the online forums.  A ground and an incoming and outgoing wire. Thanks for all the help. I will let you know how it works. If it gives me too much trouble I will take the old Commander 950 system off and install a new intake and run a carb or go with a Holley Sniper efi system.

I have had a new a aluminum radiator installed. The turn signals are fixed and the heat is working, it took tons of work purging the air from the heater core. Once I get the engine running well it will be time to drive the wheels off of this GT40 replica because that is what I bought it for. I encourage everyone to get out and drive your special cars all you can.

Prolific rewrote their drivers so they wouldn't work with pirated chipsets. Genuine Prolific hardware wasn't affected. While I can't blame them, it backfired because angry customers flocked to FTDI.

Not so. I bought a Prolific adapter from Radio Shack in the late 2000s and it stopped working in early 2020. I seriously doubt the Shack would sell a pirated chipset, but I guess maybe? But yeah, I went to FTDI.

Jimmy, today it's 23F with 10-15 mph wind. I'll wait for warmer weather, thank you very much! LOL!

Last edited by DannyP
@DannyP posted:

Not so. I bought a Prolific adapter from Radio Shack in the late 2000s and it stopped working in early 2020. I seriously doubt the Shack would sell a pirated chipset, but I guess maybe? But yeah, I went to FTDI.

@DannyP that is odd. The issue I mentioned happened a short while after I became a ham, so 2013 or 2014. I got stuck with a couple of useless adapters. Perhaps they obsoleted an early chipset? Manufacturers do that on occasion.

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