1990 obs speedo connection

[exboatracer]

No, I dont have any kind of test equip of that sort. Here's what I found,in the red connector,I have a grn/blk wire in pin 20,a solid purple wire in pin 21, and a grn/wht wire in pin 50 that is labeled speedo. The speedo wire was left out of the harness intentionally for me to hook up.This wire-the grn/wht from pin 50 is the one I'm trying to hook up to the yellow and purple wires thats coming from c-100 in my truck's original wiring. Is this ok so far? Thanks for the help gag.

[Mickeymotormount]

I ended up using the dark green/white wire from pin 50 of the red connector and ran it right to the speedometer. I undid the guage cluster, pulled out the light blue/black wire that is in position S on the plug feeding the instrument cluster. I then cut the light blue/black wire that was in position S and soldered the dark green/white wire to the end of the wire so as to reuse the little connector and then reinstalled the wire back into position S on the plug. Voila, speedo worked.

Hopefully, your wiring harness is similar. I'm using a 1993 wiring diagram from a Chevrolet C/K service manual.

Do you have cruise control? If so, it's a slightly different setup.

Let us know how you make out.

[gagliano7]

Do you have pins 20 and 21 connected to the vss in your tranny?If not you will not get a reading on pin 50 .I connected pin 50 to the speedometer wire that came out of my drac box behind the glove box.I think the 1990 has a different setup.

Here is some good write ups that my help you out

http://www.ls1truck.com/forums/lsx-t...-wiring-4.html

http://www.ls1truck.com/forums/lsx-t...gmc-k1500.html

http://www.ls1truck.com/forums/lsx-t...eter-help.html

http://www.ls1truck.com/forums/lsx-t...eedometer.html

http://www.ls1truck.com/forums/lsx-t...eter-help.html

[exboatracer]

You guys are too kind,flooding me with all this good info. The first thing I'll do is check to see if pins 20 & 21 go to the vss plug and then move on from there. With all this help I know I'll get it working. Might take a day or two and I will let you know. Thanks again.

[Mickeymotormount]

Yes, my VSS wires go to the PCM. Without it, the PCM doesn't have any referencing speed signal coming from the vehicle. I also have the DRAC box behind the glove box and ended up jumping the wire from the Cruise control right to the speedometer wire, thus bypassing the DRAC box. I was having Cruise control issues and it ended up being the '99 cruise control box that I got from the Silverado 6.0 donor vehicle was junk. I just ended up using my '93 cruise control box and switched out the cable from the '99 box so it would reach the throttle/air valve at the front of the engine.

[exboatracer]

I checked and pin 20 & 21 from the pcm are routed to the vss, so at least that part is confirmed. Still not working though. Some guys say it can be done but they dont remember,maybe something will jog their memory. The truck runs great,lots of power and a blast to drive so this speedo thing is not a big crisis when you look at the big picture,but it would be nice if it worked.

[1991SSP]

On my 1994 model, I pulled out the cluster , then pulled the plug that goes into the back of the cluster out from the dash as much as I could, on mine there was 1 wire that came from the DRAC box to the speedo , I clipped that wire and connected it to the wire coming from my harness. I used a stand alone from Nelson, they had the speedo wire labeled on my new harness.. This is the easiest way by pass all the other OEM stuff on the truck IMO

The Speedometer wire on the plug that goes directly into the harness is LT Blue/Black on my schematic for a 94 model

[exboatracer]

I also have a Nelson harness and they left me a green and white wire labeled speedo coming from pin#50 on the pcm for me to hook up. Mickeymotormount also mentioned a lt blue and black wire on his 1993 truck so I'll have to pull the cluster and try that. I'm not sure about the drac box that everyone talks about,hell,I dont even know what it is (lol), but I'm not quitting! Thanks.