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Discussion Starter · #1 ·
Alright. So I’m having some issues with my speedometer and the PO was obviously a danger to wiring.
I have wire nuts under the truck and hacked up wiring.
I am replacing the main connector on the 80e due to the wires being exposed in two spots and the lite blue wire basically loose in the socket. A simple tug will pull it right out.
Now I removed the k3500 transfer case harness that goes to the 80e and yanked it all the way from the actuator and removed that relay.
I no longer have the BW transfer case. I’m using the 261. My question is, does it make sense that the bare wiring on the main connector is the reason that my Speedo doesn’t work? Parts are in the mail so I’m just waiting and then I’ll know for sure but wanted to gather some thoughts.
Second idea I’m kicking around.
I want to keep that relay eliminated.
I plan on going with a mechanical actuator.
what wiring NEEDS to go to the diff to keep the 4x4 light functioning?
If it’s not too annoying I might use that dorman 600-600 kit with the 601 and convert to the electric actuator but I’m curious how the two plugs still function by just tapping in the brown tire to a 12v key source off the 4x4 circuit. (Brown wire at trans)

also pondering eliminating the “dummy”vss plug on the 80e and routing that to the vss output on the t case.
Trying to eliminate some of the haggard wires and I don’t see a factory harness anywhere.
K
 

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Discussion Starter · #2 ·
644767
644768
644770
 

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Discussion Starter · #3 ·
Looks like I’ll be doing the mechanical actuator (cable)
Then just wire up the solenoid switch.
Should minimize some wiring and still function.

lemme show ya.

will changing the wiring from this.
to the second picture still function using a pull cable actuator and maintain the 4x4 light

644771
644772
I’m in in
 

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Do you have the old thermal actuator or the newer electric version?
 

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Discussion Starter · #5 ·
Do you have the old thermal actuator or the newer electric version?
It’s currently the old thermal actuator.
while I have you here.
what is the blue and purple wire for here?
I can’t find it in the schematics.

the other two here are VSS and this is the “jumper”connector?

644773
 

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Must be from the 93, 94-up do not have that connector.
3500 4wd diesel schematics are sketchy in the GM SM's.
The 93 TCM used BOTH speed sensors on the 4L80 AND the VSS on the x-fer case.
Those may be for that, but the colors are wrong and they would be twisted pair.
Where do they go to? Looks like they head off in a sleeve. Is there a conn. at the other end.
The other 2 should go to the VSS on the x-fer case.
 

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Discussion Starter · #7 ·
Must be from the 93, 94-up do not have that connector.
3500 4wd diesel schematics are sketchy in the GM SM's.
The 93 TCM used BOTH speed sensors on the 4L80 AND the VSS on the x-fer case.
Those may be for that, but the colors are wrong and they would be twisted pair.
Where do they go to? Looks like they head off in a sleeve. Is there a conn. at the other end.
The other 2 should go to the VSS on the x-fer case.
So the big 4 pack connector had a transfer case harness plugged into it.
off the big one one set of wires plugged into the rear “VSS” of the 80 then the other set runs down to the back of the transfer case.
pictures attached.
mom the other side of the big connector you’re right the wires are wound together a little farther into the loom.
These wires are from the main harness. I pulled em up into the engine bay for ease of examination and wire damage repair
644775
644776
 

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Discussion Starter · #8 ·
Transfer case “jumper” harness side
644777

This little guy plugs into back end of the 80
644778

Whole harness for the 4x4 k3500 version.
I attempted to patch the wire but spots to see if I could get the speedo working. Once I get this all figured out it’ll all be soldered and heat shrunk.
 

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That is what you have, those are the correct wire colors for the rear VSS on the 4L80.
Not sure what the PO was doing there.
Too much wire. You do not need any of the synchronizer wires or the relay.
You should get the updated electric actuator, modify the harness and be done.
I can send you the info to do that.
Better now than after you find out that old thermal actuator does not work and you have to re-do the harness... again.
The VSS signal from the x-fer case speed sensor goes to the VSSB and then a signal from the VSSB
to the speedometer.
 

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Discussion Starter · #10 ·
That is what you have, those are the correct wire colors for the rear VSS on the 4L80.
Not sure what the PO was doing there.
Too much wire. You do not need any of the synchronizer wires or the relay.
You should get the updated electric actuator, modify the harness and be done.
I can send you the info to do that.
Better now than after you find out that old thermal actuator does not work and you have to re-do the harness... again.
The VSS signal from the x-fer case speed sensor goes to the VSSB and then a signal from the VSSB
to the speedometer.
Cool yeah if it looks like it’s all going to work right I’ll go that route.
To avoid this wiring mess I was going to use that 4x4 posi lock kit. The synchronizer section will be removed.
I’m pretty close to going to the wrenching yard and snagging a harness extension but I’m sure it’ll have its own issues.
What do you think the odds are the 3 bad wires on the 80e plug caused my no speedo issue?
 

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The main tranny conn. has nothing to do with the speedometer.
 

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Discussion Starter · #12 ·
The main tranny conn. has nothing to do with the speedometer.
Dang it

The VSSB is located behind the glove box correct?
And if you don’t mind I’ll take that info on the electric actuator.
Thank you sir.
 

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Discussion Starter · #13 ·
My guess is tapping into this brown wire is the 12v feed I need for the electric actuator?
Then run it down and around with the other actuator solenoid and switch wire?
That should save me having to buy the dorman600-600 wiring?
Also deleted all the synchronizer wiring, I’ll fix the connections next ohm it out and wrap it.
This wiring on the k3500 came down by the glow plugs and down over the starter. Where does it run on the k1500-2500 ones
644794
 

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You may want to see if the electric actuator fits your axle.
A GM TSB notes that it will not fit pre-94 K3500's. IIRC there is a clearance problem on some 1-ton axles.
Never fails. You may need to keep the thermal unit.
If you keep the thermal actuator then this is all you need since you are not using the BW x-fer case.
The VSS wiring is not on this schematic. It just happens to run in the same bundle of wires.
You are missing both the connectors that go to the front, the actuator and the switch.

644796
 

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Discussion Starter · #15 ·
The connectors are around here some place.
They were put together with the speed nuts so I pulled them off. I’ll solder them together at some point. Ill add the extra power wire in case I end up being able to use that actuator.
Might even go grab a test one from ole pick n pull to see.
I tested the wires for going to the VSS and they seem to have continuity. But before I started playing with these wires the speedo didn’t even flicker. I’ll test the VSS itself and check for signal at the VSSB and keep my fingers crossed.
 

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This may help with the VSSB.
 

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Discussion Starter · #17 ·
Well as @Glagulator promised. Repairing the 4l80e harness did nothing for my speedometer issue.
I was hoping it would at least assist with the lack of shifting. All I did at this point was tidy things up lol. Pulled out the VSSB and tested across pins c7 and c12. I have an AC signal. Speedometer is still buried at zero.
Given this information where should I stick my probs next good fellas?
 

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Discussion Starter · #18 ·
Also have power from c9 and c8.
That can/should rule out the bad ignition switch.
 

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Discussion Starter · #19 ·
After back probing c8 and c15
I see under 1 volt.
For the signal reference pin… spacing which one that was now… I’m not seeing the 5v but more like .090
 

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Discussion Starter · #20 ·
Might run to the JY and snag a box. See if it helps with the output signal.
 
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