I know this has probably been done before but I figured being I needed to do it, I would try to make a picture friendly thread. I recently changed the tires on my 1990 348 to a shorter tire on 360 wheels. 215/40/18 Potenza RE-71R and 265/35/18 Potenza Sport. Image Unavailable, Please Login This cause my speedometer to read 50mph when I was doing 43mph on my GPS. I purchased the speedometer correction kit from 12o'clock labs. Below are the parts I purchased. Image Unavailable, Please Login Here are the instructions that come with the kit. The kit will have 4 wires you need to connect. RED, BLACK, GRAY and ORANGE. Image Unavailable, Please Login Start by removing the gauge cluster. There are to screws that are on the bottom. The picture will show the attachment point for the screws after they are removed. Then you simply lift from the bottom and unhook the top and unplug the connectors. Image Unavailable, Please Login This 5 pin connector is the speedometer connector. Image Unavailable, Please Login About 5 inches from the connector I cut the red/black wire (second pin the speedo connector). Image Unavailable, Please Login You connect the GREY wire to the RED/BLACK (from the speed signal end) and the ORANGE to the RED/BLACK )going to the speedometer connector. Image Unavailable, Please Login Cut the GREEN/WHITE wire on the same speedometer connector harness and splice the RED wire to it. Image Unavailable, Please Login Image Unavailable, Please Login Then I grounded the BLACK wire to a contact point behind the cluster. Image Unavailable, Please Login Then reassemble and program the kit to following instructions. My GPS said I was going 43mph but the speedo was saying 50mph. (43/50 * 100) - 100= -14.0 -14.0 is what I need to program to the unit. Here is the video link to program it. SpeedoDRD v3.8 and v4.0 Setup - YouTube It worked perfectly and it is a 35 minute job if you do not suffer from "Analysis Paralysis".