| Re: speedo inop |
Subject: Re: speedo inop by anesthes on 2009/5/19 13:51:17 Gm speedo electrical is tricky. Normal applications have a 4-out buffer. Speedo in, one wire out to the ECM, another to the dash. So the two wires (purple and yellow) from the VSS go into the buffer. Brown wire is 4k PPM output to the ECM. Green with black stripe goes to the cluster. Black/white is ground, and pink/black is power. However, on your '85 the cluster IS the buffer, and sends a 4K ppm signal to the ECM. The good news is, the "speedo" and "buffer" are independent circuits. My starting point would be to plug a scanner into the ALDL port and see if you see a valid MPH while driving. This would prove the VSS good. If you don't, it still could be the VSS signal, the buffer, or wiring. I have scanned copies of the manual, as well as notes if you need help trouble shooting. C4 electrical is a pain. I abandoned my dash swap on the '87 I used to have because I just didn't want to be chasing down gremlins for the rest of my life. -- Joe |
