7 pin mod ….what is it? (8 Viewers)

Joined
Oct 28, 2022
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5
Location
Albuquerque
I have a 94 80 series that the center diff locks without fail when I put it in 4low but won’t disengage when I go to 4HI.
I have been able to disengage the lock with a 9 volt battery a handful of times.
I bought a diff lock button to see if that will help before replacing the trans relay
My question is can I just install the button or do I need to do the “pin 7 mod”
What does the pin 7 mod accomplish?
Thank you as always for any insights!
 
Joined
May 6, 2011
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1,149
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Davis County, UT
Lots of info if you search, but to answer your question the button is plug and play. Pin 7 mod allows you to go into low without locking the center, while the button allows you to engage the cdl regardless of the transfer case position. So you don't need to do pin7 with the cdl button, but you do need the button if you pull the pin (otherwise you'll have no way to lock the center)

Your issue seems separate from these controls, though. I have a feeling you'll be testing limit switches and tracing wires
 
Joined
Oct 28, 2022
Messages
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Location
Albuquerque
You were right....the button didn't make a difference. I've got a new transmission relay on the way. I'm hoping that will solve the problem. I am not looking forward to digging in deeper if it doesn't.
thanks again for the insights
 
Joined
Apr 14, 2016
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Oregon
I've got a new transmission relay on the way. I'm hoping that will solve the problem.

Why would it?

IIRC, there are three switches on the transfer case that tell the computer what the state of the transfer case is. 1) Low range, 2) CDL locked, and 3) neutral position.


Not having looked at the FSM at all, my complete guess is that your low range switch is sticking, so it this is still in 4-low and doesn't unlock the transfer case. The switches seem to be far more troublesome than any other component in the transfer case, hence my guess.

Here's a guide to cleaning them, which may or may not work:


There's a Dorman switch (Tacoma reverse switch?) that can be substituted for one or more of them if they test bad and cleaning doesn't work. I don't remember which of the three can be substituted.
 
Joined
Oct 28, 2022
Messages
5
Location
Albuquerque
I've replaced the transmission relay/control module, the L4 and neutral position switches, and the vehicle speed sensor. The "shaft" on the new vehicle speed sensor was shorter than the original that came out of the case so I used the one attached to the original for better fit.
The center diff still locks after placing the vehicle in 4L and then placing in Drive. When I take it out of 4L and go back to 4H, the diff remains locked. Driving straight forward at around 5mph (per FSM) doesn't unlock the diff. Driving in reverse while turning full left to full right (per other online advice) doesn't unlock the diff. The center diff lock switch I installed doesn't unlock the diff.
I don't know what to do next other than replace the actuator.
I thought that if it locks when putting the vehicle in 4L and unlocks manually with a 9 volt battery that it should be fine.
Is it possible that it unlocks with a full 9 volts from a battery but might not be getting enough energy from the electrical system to actuate?
What else might it be?
 
Joined
May 6, 2011
Messages
1,149
Location
Davis County, UT
Again,
Your issue seems separate from these controls, though. I have a feeling you'll be testing limit switches and tracing wires

I wouldn't fire the parts cannon anymore. Your actuator is fine if it's doing it's job with a 9v. Dig in and get familiar with the wiring system, it'll be a service to you and your rig. We're here to help. Start with a multimeter and see if the actuator is getting power. The ewd, which is free if you Google it, has an entire "diff lock" section
 

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