1990 obs speedo connection

[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.

[1991SSP]

By finding the wire on the cluster plug you are bypassing everything and going straight to the speedometer...

[exboatracer]

Ok,I pulled the cluster and don't have a blu/wht wire.Didn't think there was one cause I couldn't find one on the schematic. After lots of research (homework you guys gave me lol) I found out that the 1990 trucks dont have the white drac box with the blu/wht wire. It's built into the cluster making the hookup more involved requiring a dakoda digital module or a high dollar reluctor wheel from s&p.Here's what I'm doing--- putting an aftermarket electric speedo from Speedway motors P/n91065051 in place of the stock speedo head which will just unplug from the cluster. I'll make a brushed aluminum face plate and mount the 3 3/8 guage dead center. The body of the guage is 1.6" deep so it will clear the circut board. I like the looks of the guage and also the fact that it will give the dash a different look. Just want to give all who helped me on this,and with my build in general a BIG thankyou. I'd like to shake your hands someday.

[GraniteBlueNNBS]

Thats good to know as my future project is a 89 rcsb, but i was already thinking of going with Autometer gauges since my bro already pulled out the stock cluster.

[exboatracer]

Just an fyi on the speedway motors speedo. I got mine today and it will not fit as easy as I described in the above post.I will make it work with some cutting and slicing. The spec sheet on the ad says the speedo body is 1.6" deep which is correct, but the mounting studs and backlight make it around 2 3/4" deep. Sorry for the bad info, I should have installed it before I said anything.

[Mickeymotormount]

Can't you update to a later guage package? I have a couple that I'm not using and would be glad to help out. They're out of a 94 model with factory tach. It may be alot easier than hacking up your dash.
I'm sure there are differences in the wiring, but nothing too complicated.

[Venom]

Ok,I pulled the cluster and don't have a blu/wht wire.Didn't think there was one cause I couldn't find one on the schematic. After lots of research (homework you guys gave me lol) I found out that the 1990 trucks dont have the white drac box with the blu/wht wire. It's built into the cluster making the hookup more involved requiring a dakoda digital module or a high dollar reluctor wheel from s&p.Here's what I'm doing--- putting an aftermarket electric speedo from Speedway motors P/n91065051 in place of the stock speedo head which will just unplug from the cluster. I'll make a brushed aluminum face plate and mount the 3 3/8 guage dead center. The body of the guage is 1.6" deep so it will clear the circut board. I like the looks of the guage and also the fact that it will give the dash a different look. Just want to give all who helped me on this,and with my build in general a BIG thankyou. I'd like to shake your hands someday.

Do you have the part number for the dakota digital module to run the 2002 4l60e trans with the 89 stock cluster?

[pmcarbuilder]

seems like there should be a was to use the 1990 speedo work,Im trying to get one going myself,could I just use a cluster from a 1992 c1500 with out rewiring?

[88stepside]

I spent a lot of time on my speedometer cluster when installing the LS1 in my 1988 RCSB. Here is the info on 88-91 speedometers, the cluster has circuits inside that perform the same functions of the DRAC in 92 and later trucks. As in, speedometer driver, speedometer correction, RWAL (antilock brakes), cruise control output, speedometer out to ECM.

88-91 the Yellow and Purple twisted pair wires come off the trans tail VSS and go up the firewall and into large square firewall connector harness near power brake booster. These wires go through connector in firewall and straight into speedometer cluster. The signal the VSS produces is a simple AC square wave signal, the VSS is a magnet reading a toothed ring with 40 teeth, and that 40 pulse signal is what your speedometer needs to work. 88-91 speedometer clusters then condition the VSS raw signal and send it out to everything else, antilock brakes, cruise, original ECM.

If you are using an automatic trans in your swap just jumper off the VSS wires, at trans, at back of speedometer, it doesn't matter, and run them to your new ecm. I don't know why you would though, usually all your new ECM needs to know is if you are moving or stopped. The speedometer output from back of cluster that went to old ECM can be run to new ECM speedometer input pin. Your new ECM is not controlling cruise, antilock brake, or speedometer, as those functions are retained in original cluster if you uncap the yellow and purple wire and run them back up to firewall connector, twist the as they were originally to suppress any noise.