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Wiring harness help

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Old 03-03-2018, 07:38 AM   #1  
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Wiring harness help

I'm looking for a little wiring harness help fellas. I've got a 1990 with an automatic transmission. Previous owner had all the wires going down to the transmission hacked and spliced. I'm working on cleaning this up but can't figure out which wires go to the speed sensor and transfer case. The speed sensor has a white/orange strip, and Brown with blue strip, which I can't find in the harness on the firewall. And there's a solid blue and solid black that are both bigger than the rest of the wires in the harness..?? I have the correct wires for the transmission plug.. But the others??
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Old 03-03-2018, 09:56 AM   #2  
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As I recall, a 1990 has a mechanical speedometer and no speed sensor.

According to the 1991 diagram, so perhaps different, the transfer case swithc is LG/BR and BK .

I'm not quite sure where you are breaking into the harness, but the solid blue and black sound like the main ignition circuit and ground . . .

Do you have a 1990 wiring diagram?
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Old 03-03-2018, 10:26 AM   #3  
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Quote:
Originally Posted by Alec View Post
As I recall, a 1990 has a mechanical speedometer and no speed sensor.

According to the 1991 diagram, so perhaps different, the transfer case swithc is LG/BR and BK .

I'm not quite sure where you are breaking into the harness, but the solid blue and black sound like the main ignition circuit and ground . . .

Do you have a 1990 wiring diagram?
I have a gas 90 w250 the speedometer is electric I pulled all the wiring and used a 93 harness for my Cummins conversion if you think the color coding is the same I can look at it
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Old 03-03-2018, 04:58 PM   #4  
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Originally Posted by Alec View Post
As I recall, a 1990 has a mechanical speedometer and no speed sensor.

According to the 1991 diagram, so perhaps different, the transfer case swithc is LG/BR and BK .

I'm not quite sure where you are breaking into the harness, but the solid blue and black sound like the main ignition circuit and ground . . .

Do you have a 1990 wiring diagram?
no I do not have a wiring diagram. There is a plug on the side of the transfer case for the speed sensor it does not have a cable going to the speedometer. The wiring was cut right where the down pipe is. I ran the truck a couple years, but got into a ditch plowing with it and busted the flange off the down pipe and the heat melted all the wires from the exhaust. For whatever reason the p.o. used all the same color wire to connect the harness to the plugs... I just pulled them up to where they connected to the harness and cut them off figuring they are color coded and it should not be a big deal to fix.. the plugs have some factory wires still on them..
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Old 03-03-2018, 08:34 PM   #5  
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According to my '91 manual, white with orange is the speed sensor wire from the sensor, through the connector under the alternator regulator, to the bulkhead connector (pin #43), to the circuit board on the speedometer head. It calls for the other wire to be Black Light Blue, which joins a common ground for various sensors in the engine compartment (and does not go back through the bulkhead connector, I think it grounds on top of the intake manifold plate).
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Old 03-04-2018, 10:24 AM   #6  
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Tan/Orange and Black/light Blue got to the speed sensor. It is mounted on the transfer case, not the transmission.
Light Green/Brown and an unidentified goes to the transfer case switch.
White, Brown/Yellow, and Violet/Black goes to the backup and neutral safety switches connector on the side of the transmission.

This is the OEM wiring. If yours has been modified, good luck.
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