Namu

I have a 1993 silverado that was originally a 2wd with the 6.5 turbo and a 4180E but when it came into my hands it was converted to a 5.7 tbi with a 5 speed and 4wd. When I got it neither the tach nor the speedo worked. I knew the tach problem was because of how diesels got their signal from the alternator, and since they pulled that wiring harness I'm sure they never bothered to get it to work once the thing could drive. What I chose to focus on was the non working speedometer. First I checked my transfer case, and it had the speed sensor in there and unplugged so it was caked with mud. I went ahead and changed the sensor and the connector because it had the same problem. No signal. I looked at the wires leading to the firewall and they had touched the exhaust and melted, so I ran new wires up to the firewall connector, and still no signal. At this point I was pretty bummed out about all of that but went ahead and swapped the dash cluster because the previous owners had gotten their dirty paw prints on it and ripped the paper circuit board on the back of it. Still no FRIGGIN SIGNAL. But now my high beam, left turn, and parking brake lights work so it was totally worth it. So then I kinda sat on it for a while and one day while fumbling with my A/C settings after plugging my battery back in, the speedometer suddenly started working. I like to have **** myself at this point because of the amount of aggravation and time I had put into this thing and to have it work randomly like this was just the final kick in the ***** for me. I got up to 5 miles an hour and it dropped dead again. So I went all in and stripped my dash down to try to find where there might be a chafed wire or somethin but only found some stupid nonsense where they cut a blue wire and a pink wire and twisted them to where the pink wire was connected to itself and the blue wire on the other side of the connector behind the glove box. I cursed them for doing that stupid crap and connected the wires to their respective colors, put everything back the way it was, and went to start it, but the truck wouldn't fire. So I instantly knew that blue must have been ignition and they were too lazy to fix the problem and just tied it into a 12v wire. So now this is where I am at with this speedometer. New speed sensor, connector, wires straight to the firewall, I think the firewall plug is fine, but it is full of this weird black silicone feeling stuff which is not what I thought would be in there, from what I can see the purple and yellow wires are in it's factory harness straight up to the dash cluster connector, and it does T off to my DRAC module, which is also brand new. If anyone has any ideas as to what it could be I'm open to hearing them. I'd like to know exactly what those blue and pink wires were, and maybe the colors of all the wires related to the speedometer and the pinouts for the drac module if anyone has those resources. Sorry for the long post, thanks for reading.

Gumby22

Regardless of the engine/drive train combination, the VSS and speedo circuits (circuits only - the sensors are different between manual and auto) should be the same with the exception of the location of the VSS. The DRAC module is compatible with either sensor type.

Below is a wiring diagram for the DRAC module and speedo circuit - I had to zoom in for the details but the DRAC sends a signal directly to the cluster (marked on the cluster side by the red line). Note the DRAC has its own ground and ignition feeds so I’d recommend verifying those are good as well.

The tach is fed directly from the ground side of the ignition coil.

If the PO did a hack job on the wiring, I recommend buying a service manual such as Chilton or Haynes or getting a temporary subscription to All Data, Pro Demand, or Identifix.