I'm trying to understand all of this speedo fix with the DD Sgi-100bt. I've read so much on the forum and no one can seem to have the same opinion or a solution similar to mine.
I have a 1990 Firebird V6 car. Replaced V6 with a SBC and Transmission with a 700r4. The speedometer is maxing out now when in drive. I purchased and installed a DD Sgi-100bt. Took the purple and yellow vss wires from the ecm and used them into the DD input and ground. The brown wire from the ecm from the speedometer to output #3. This does not stop the speedo from maxing out to allow any adjustments. I've tried different settings in the DD Sgi-100bt and different outputs for the speedo. I know the DD is communicating to the speedo, because I can make an adjustment or run a text in the DD app and the speedo will react for a few seconds.
Can someone that understands this offer me some help?

 

If the 700R4 came from a 85-90 firebird or 90-92 f-body all you’d need is a buffer box like displayed above. Tbi cars have them. Should be able to get one from a local junkyard. 90-92 would be the one you need. However if the transmission is from a s10 or newer F-body you would likely need a SGI-100BT from Dakota Digital. I’m doing a LT-1 93-97 T56 swap I’ll have to use one. As my Speedo now reads 67mph going 5mph. I know you post is from last year just wondering if you ever got it figured out?