Jimbo, you are going to have to use the ABS speed sensor in the diff which is a different animal from the VSS. Still generates a low voltage signal though.

I think that box is about the only way I've seen to do that. I bet it'll work.

 

i do too. just lazy feeling right now and figured i could get a faster answer from the gurus here . i wasn't trying to argue with you about it for sure. guess i should've stated that it had a getrag in the beginning. i'd appreciate any info about it if you so happen to find a pulse spec

 

The box will be changing the pulse rate, not the voltage. I doubt the speedo is very picky about the wave form or even the voltage so long as it sees pulses.

 

i'd sure hate to tap into the signal wire and it not work though . not saying that it won't at all. but after reading the installation instructions for the interface, it says not to use it in conjunction with an abs system. as quoted in the description...

"If your vehicle is equipped with an anti-lock braking system (ABS), it is generally advised to ensure the signal reaching the ABS controller is not altered to eliminate any potential problems affecting control algorithms within the system. Some vehicles also utilize the output shaft speed to calculate transmission slip and lock-up. When a signal feeding the PCM is altered, this may cause the PCM to detect a constant slip. Consulting a service manual may be of assistance in determining the signal routing within the vehicle if the SGI-5 is decided to be used in a situation such as this."

i have no pcm to worry about though. but again, i'd hate to tap the signal wire and screw up my system somehow.

 

Here is some information on Speed Sensors; they all seem to have outputs that generate pulses varying from both Square Wave and Sine Wave AC outputs and the higher the pulse count per mile the higher the resolution.

Since the speedometer in manufactured by VDO this is what I am basing my theory from, maybe sometime I can spin my VSS and check the output on my oscilloscope.

http://www.egauges.com/pdf/vdo/0-511-011-348.pdf

http://www.jagsthatrun.com/V8-chapte...ed-Sensors.pdf

This place has Ratio Adapters that some of the members have asked where to get.

http://www.partshp.com/speedometer_gears.htm

The speedometer will probably work just looking at a string of pulses.

Jim

 

Are you sure about that? I've always read it was only the '89 trucks that had the cable driven speedo.

While we're on the subject (kind of) can someone post a picture of their '90 instrument cluster? Is it the same as the '89 or is '90 the year they changed?

Thanks (sorry for the threadjack)

 

here's my dash....

 

My comments in red. No need to be timid, try the box!

 

'90 was the first year for the electronic speedo. Of the factory Cummins trucks, only '89's would have the cable drive speedo. It doesn't really look any different from the driver's seat.

 

thanks dave! so where to tap in is my next question? should i tap in around the sensor in the rear end or somewhere up near the cab? if i can follow the wires up near the cab and tap in there, that would help being able to calibrate it as i could keep it on the seat next to me to adjust it.

 

I'd use the "rolls" connector right by the hood release.

 

what does it look like and what color wiring? sorry for all the questions. not very electrical savvy.

 

It's a little 2 wire plug right under the dash. The wires are red/purple and white/purple I think. The giveaway is that the wires leading to it are twisted together.

 

thanks again dave. so the abs controller is under the dash i take it? is there a constant 12v to one of the wires with the ignition on? and would that be the wire i tap into?

 

ABS controller is behind the glove box.