Need some speedo help

[twithers]

I picked up my 88 C15 with a Turbo 400 transmission installed. The tranny has the cable speedo port and the truck has an electronic speedo.

After talking to my tranny guy, I picked up a pulse generator that screws into the cable speedo port on the tranny and generates the pulse that the vss would in a stock setup.

Here's a link to that pulse generator:
http://www.ezwiring.com/store/viewitem.php?productid=74

The wiring all the way to the plug at the back of the gauge cluster appears to be good.

I pulled the gauge cluster to clean it up and see if anything needed repair, but found nothing to fix.

After all that, the speedo still doesn't work. Any ideas what I can look into next?

Thanks.

 

[Jrgunn5150]

What speedo do you have?

I know for 4x4's they went electric in 90 I believe, prior years were cable driven.

I'm probably way off track here lol, are you getting any action out of the speedo at all?

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[Jrgunn5150]

And on further reflection, I'm probably totally wrong about that, because that info is for K5's....

These trucks came with TH400's in the heavier models. At this point I'm just subscribed for learning, sorry I'm not help lol

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[THEFERMANATOR]

Have you conencted a DVOM to see if your pulse generator is putting out a signal? The early trucks have the DRAC built into the cluster I believe, so they are a bit different than later years. I would start with the basics and go from there. Make sure you have a voltage signal from your pulse generator, then back probe it with it hooked up to make sure it is still there. Then check to see if it is making it to the cluster at it's wiring. Also make sure all your speedo wiring is twisted as noise interference can cause issues with magnetic signals that produce AC output voltage.

 

[twithers]

Sorry it has taken so long to get back with you.

Before I installed the pulse generator I hooked a meter to it and it put out a voltage as I spun it.

After that, I checked for continuity in the twisted pair up to the plug at the back of the gauges. And tried swapping the wires, with no luck.

I'm working alone, so I haven't been able to check for voltage from the generator up to that same plug, as it would require me to measure while driving.

At random times, I'll be driving and look down and the speedo will be sitting static at 10mph, but there is no consistency to it. Sometimes it will do it and sometimes not. When it does, the needle does drops as soon as I turn off the truck.

Other than that, there is no function from the speedo and consequently nothing from the odo/trip meters.