Originally posted at gtplanet, but I'm hoping there is more knowledge of wiring here.

Since there are no purchasable pedals to upgrade the DFGTs stock pedals, I wanted to be able to use my G27 pedals with the DFGT without making them unusable on the G27. The G25/G27 pedals have a different pinout than the DFP/DFGT/etc. pedals, so I needed to build an adapter to connect them.

After a long search, I found what seemed to be correct pinouts for both sets of pedals, listed at the bottom of this post.

I got the parts I needed at radioshack, and built and tested a custom DB9 cable using the pinouts below. After hooking everything up, the brake pedal worked as expected, but the accelerator worked backwards, fully on except when pushed and so on.

I'm sure something is wrong with the pinouts I used, but I have no idea where to start trying to fix things, so any help would be much appreciated.

G25/G27 pedals pinout:
1: Ground
2: Throttle
3: Brake
4: Clutch
5:
6: +5V
7:
8:
9: +5V

DFGT/DFP/Black MOMO pedals pinout:
1:
2: Throttle
3: Brake
4: Ground
5:
6: +5V
7: Throttle
8: Brake
9: Ground

P.S. This is exclusively for use on a PS3, so the leo bodnar USB pedals adapter will not work.

I don't think your pinouts are wrong, it might just be the wheel controller expecting a high value with the original pedals and you're giving it a low value with the new pedals. You might be able to use an inverter (a NOT gate) to invert the value and send it to the wheel, it might solve your problem. But, this is trial and error, you just have to try a few different things, and hopefully one might work. On the other hand, you might end up damaging your wheel if you give it too much voltage, so be careful.

Does the G27 pedal use a potentiometer like the DFGT? If so you could just grab a soldering iron and switch both outer cables on it, the middle one is ground.