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'94 Speedometer and Odometer Not Working

Big T

Big T

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The speedometer on the '94 finally broke for the PO just before we bought it. It had been giving him problems for awhile. A couple times on the drive home, it would flip up to speed and then back to zero. 99% of the time it was zero.

So I got a new (used) known to be working gauge cluster from War Wagon here. Got that installed and everything is working but the speedo and the odometer. We pulled and checked the speed sensor on the transmission. The plug and wires to it were in good condition. War Wagon put an ohm meter on it and rubbed a magnet over it. The readings convinced him it was good. I pulled the speed buffer from behind the glove box of the '95 and swapped that in and no go.

Seems like we're running out of things to check. Is there a speed sensor on the transfer case? Any grounds that I should be checking?
 
If there was a problem with the speed sensor or VSSB, then it would go into limp mode and only give you 2nd gear. Sounds like a wiring issue between the VSSB and cluster.
 
NVW said:
I'm not 100% but I think the output speed sensor is on the transfer case.

They can be bought here: http://www.electricaladvantage.net/4l80espeedsensorkit.aspx
Click to expand...

There is a second speed sensor towards the rear of the transmission, but there is nothing plugged into it and I could never find an available wire with plug to go in it. Nothing obvious hanging around back there, just the one in the front had a harness plugged into it.
 
Big T said:
There is a second speed sensor towards the rear of the transmission, but there is nothing plugged into it and I could never find an available wire with plug to go in it. Nothing obvious hanging around back there, just the one in the front had a harness plugged into it.
Click to expand...
Mine is the same, I've never looked but I think there is one on the transfer case. Otherwise the speedo would be off in Lo Range.

Ferm is probably correct in his answer. He knows his stuff.
 
Big T said:
There is a second speed sensor towards the rear of the transmission, but there is nothing plugged into it and I could never find an available wire with plug to go in it. Nothing obvious hanging around back there, just the one in the front had a harness plugged into it.
Click to expand...


The 2nd speed sonsor in the trans is a dummy to fill the hole. 91-93 4X4's and 2X4's used that hole for an output speed sensor, but 94+ 4X4's used the one in the transfer case. The VSSB is the white box behind the glove box that runs the speedo and feeds the output speed sensor reading to the ECM(and radio for SCV on 95+ trucks). Sounds like you have a broken wire or loose conenction between the VSSB and cluster from your description.
 
THEFERMANATOR said:
The 2nd speed sonsor in the trans is a dummy to fill the hole. 91-93 4X4's and 2X4's used that hole for an output speed sensor, but 94+ 4X4's used the one in the transfer case. The VSSB is the white box behind the glove box that runs the speedo and feeds the output speed sensor reading to the ECM(and radio for SCV on 95+ trucks). Sounds like you have a broken wire or loose conenction between the VSSB and cluster from your description.
Click to expand...

OK, I swapped the VSSB from the '95 into the '94 with no effect. The original was then put back in. I did not check the wiring, but will do that this week. Thanks.
 
Got to be at the cluster connector. The one cluster connector wire bar was popped up and with the sun in my eyes may not be fixed well. The may be other issues there like the wire coming loose from that connector bar on top.

Check what position the speed signal run on to the cluster.
 
The plug from the VSSB was at least an inch wide and multiple wires going to it. I did not take time to study that; just simply plugged it in. I also did not get a chance to take in what you did at the cluster receptor plug other than noting there were electrical tabs that were sorta spring tensioned that connected with the cluster when it was shoved in. I'm assuming that one or more of these were bent such that they were not connecting?
 
One of the connector spring wire bars on the vehicle plug that the cluster gets shoved into was popped out. So rather than having the usual curved bend for the springy connection it was popped out at the end.

I guess they may have pulled the dash and pulled the connector through it damaging it.

So I would concentrate on this connector at the back of the cluster. I would start by identifying the wire and pin number for the connector that carries the speed and odo signal. Then check it's condition at the connector. Without that info you can check the condition of the connector again concentrating at the top center left position where I noted the damage.
 
Here's a picture of all the wiring behind the glove box:
1361405342_zps45da9f5a.jpg


Here's a picture of the wiring to the VSSB:
1361405523_zpsa0638914.jpg


Here's a pic of the plug behind the gauge cluster:
1361405495_zpsfeb54a33.jpg


I believe it was the 4th connector in from the left on top that was the one you worked on. I appears to be connecting with the gauge cluster, though I have no way of testing.

Here's a pic of the back of the gauge cluster:
1361405463_zps1288ca50.jpg


I have no idea how to proceed on this. I have no way of identifying the wire and pin number for the connector that carries the speedo and odo signal. As seen in the pic of the VSSB, there are a number of wires coming out of that plug there. I was able to trace most of them to the receptor plug at the back of the gauge cluster and all of the connecting tabs appear to be in order and connecting.
 
Here's a pic of the back of the cluster showing the wiring from the plug:

1361411914_zps0d31002f.jpg


TCH1 through TCH4 are all behind the speedometer and they all take power off the tachometer pins which are off the right. The GRND goes to the #3 tab from bottom right on the plug and it's a beige colored wire:

1361405495_zpsfeb54a33.jpg



Here's a video showing the speedometer moving when I touch a 9 volt battery across the pins on the back:

 
I'm pretty sure the problem is not a ground issue as the ground contact (3rd from lower right on back of cluster) splits to provide ground to both sides of the gauge cluster and the rest of the gauge cluster is working.

I wish someone could provide a wiring diagram so that I can figure out what wires power the speedometer and odometer.
 
Thinking about it...
I am GUESSING the speedometer/odo feed is the 3rd wire on top from the left on the header. My theory is the 4th connector is too high and holding the cluster side flexible plastic connector film off the 3rd connector.

Possible fix is a piece of foam between the connector strip and the cluster plastic to add more tension to the connection on the top. Repair to reduce the 'pin' height also could work. Or a bit of both.

Should of had you turn her out of the sun when looking at that.

Don't zap the chips with 9V!

Use a voltmeter and check the 3rd and 4th dash connector wires for AC or DC voltage when moving the vehicle referenced to a ground. This could show you the speedometer/odo signal wire. At least making sure we are in the right area.
 
I studied the printed circuit board last night. That connector goes to the parking brake light. All that stuff is working and none of the connectors on that part of the plug to to speedometer/odometer.

Without a wiring diagram this is just guess work. I'm taking it into a speedometer shop.
 
Thanks AK. I had already taken the truck in to the Speedo shop by the time I saw this posted. It's really hard to read and I can't expand the size, but I'm sure it would have helped as it talks about using a test light on the green ground to the VSSB.

It should be fixed by tomorrow.
 
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