Speed sensor location?

[Big Tow]

I bought and electronic ratio adapter for my truck. I am running 285's and the speedo is off. I tried to hook it up today and couldn't get it to work. The place I bought it from only had info up to 2002 and I have an '03.

Where is the speedsensor? I thought I had found it on the tailshaft of the t-case. I spliced it into the green wire/black stripe and it didn't change the speedo reading. I figured maybe that wasn't correct and tried the purple wire/white stripe and that caused the truck to jerk badly , obviously not correct.

The '02 info was to use the green wire/white stripe on a 10 pin plug near the fuse box under the hood. Is that still valid on the '03? I had trouble finding that wire and figured the easiest way was under the truck where I could confirm that it was the speed sensor. Of course, that didn't work either.

Any help is appreciated!

[77TransAm]

Big Tow, you are looking at the right speed sensor. I know Allison frowns on tapping into it, though - seems they've encountered customer complaints where the root cause was additional equipment sharing the speed sensor signals. I guess the signal isn't strong enough to drive something else and still arrive at the TCM with enough power to function properly. Perhaps that is affecting your truck somehow when you try to tap into it?