Center diff relay

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Jan 26, 2020
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CA, USA
Im having trouble locking my center diff. Shifting to 4lo- don’t hear any clicking or buzzing. Shorted the sensor switch and my abs/central diff light went on. 30 amp fuse seems intact. Driving and playing with 4lo around does not seem to help either. My next suspicion is the relay? Unless it’s super faint, im not hearing any clicking or unusual sound when shifting to 4lo. Where is this magical relay? Tried searching but could not find a definite answer. Just located in the kick panel? Hope its just the reay, would hate to remove the actuator 😔
 

ppc

M Go Blue
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Aug 18, 2003
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Exactly which sensor switch did short? There is one on the front of the transfer case that controls the lights and there are two on the rear extension housing of the transfer case. One senses the neutral position and the other senses the low position.
 
Joined
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Exactly which sensor switch did short? There is one on the front of the transfer case that controls the lights and there are two on the rear extension housing of the transfer case. One senses the neutral position and the other senses the low position.

I did the front because it was actually broken. I have not tested the rear ones because I did not know about them. When on neutral the AT/P lights come on, does that mean the neutral sensor works? How about the relay? Should i be hearing something? Thank you
 

ppc

M Go Blue
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Aug 18, 2003
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Yes, the neutral sensor turns on the AT/P light. Pull the other connector and short it. With the key "ON" and the engine not running you should be able to hear the relay activating if your hearing is good. Do you have a CDL switch on the dash? If not then the previous owner may have done the "pin 7" mod but removed the dash switch before selling.
 
Joined
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Yes, the neutral sensor turns on the AT/P light. Pull the other connector and short it. With the key "ON" and the engine not running you should be able to hear the relay activating if your hearing is good. Do you have a CDL switch on the dash? If not then the previous owner may have done the "pin 7" mod but removed the dash switch before selling.
Do you have a diagram or pic by any chance of this sensor? I know it should be in the transfer case but it’s just a little cramped to see.
 

ppc

M Go Blue
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Aug 18, 2003
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Nashville, TN
 
 
 
If it is hard to see you must be looking in the wrong spot. You need to look at the very rear of the transfer case. Looking from rear to frnt the 4Low Position sensor switch is on the right side. If you search you should be able to find plenty of pictures and write ups. It is also well documented in the FSM.
 
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If it is hard to see you must be looking in the wrong spot. You need to look at the very rear of the transfer case. Looking from rear to frnt the 4Low Position sensor switch is on the right side. If you search you should be able to find plenty of pictures and write ups. It is also well documented in the FSM.
Ok thanks, i was looking from Front to Rear. Will try backwards. 👍
 

LINUS

Waiting for the Great Pumpkin
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Mar 29, 2003
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PNW - WA
 
 
 
Do you have a CDL switch on the dash? If not then the previous owner may have done the "pin 7" mod but removed the dash switch before selling.
Funny you mention that - I was a 2nd set of eyes on a 80, this exact scenario happened.

The seller pulled the switch to his “upgrade 80”, but obviously hadn’t checked functionality of the CDL after, so while we could switch to low, none of the dash lights for the ABS, CDL would light.

When we asked - he said, but he wasn’t a Mud guy / didn’t know what the pin 7 mod was.


Esp as older ex-Mud 80’s start getting passed around, that’s a good suggestion as really any other sites I’ve seen nobody seems adept at the pin 7 & reasons to do it.
 
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Mar 31, 2012
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Denver Colorado
 
Lately I have been having a similar issue. I would engage the dash switch and no lights or locking noise. I would shift the T-case to low range and nothing would happen either. I just started cycling the dash switch and the T-case and everything started to work normally. I think my CDL indicator switch on the T-case was sticking. You can try just cycling it daily and see if that helps.

1585234635061.png
 
Joined
Nov 18, 2019
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114
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Albuquerque NM
There is also a ground connection *inside* the actuator. If that is gummed up then the relays won't click either. I spent a while checking all the relays but they were fine--cleaning up the inside of the actuator solved my issue. But check the indicator switch first.
 
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Update. Checked the 7 pin mod, it was intact. I could hear the relay click, maybe i wasn’t paying too much attention before. So went to the 4lo switch connector, i jumped it with a paperclip and no buzzing of actuator. I could hear the relay clicking when I jump the connector though. Whats next? Remove the actuator??

Edit. I should have tested the actuator itself with a 9v battery... will try that tomorrow. What if that still does not work?
 
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Joined
Nov 18, 2019
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Albuquerque NM
What if that still does not work?
Could check the wiring to the actuator too. There are a some other threads on here that you can search for removing the actuator and giving it an overhaul. I unbolted the cross member and lowered it a few inches to help get better access to the actuator. The hardest part for me was breaking the seal of the old FIPG. I had to hammer a tiny flat screwdriver into the gap (maybe not the best method but it worked). Once the actuator is off then it isn't hard to give it an overhaul on the bench.
 
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Could check the wiring to the actuator too. There are a some other threads on here that you can search for removing the actuator and giving it an overhaul. I unbolted the cross member and lowered it a few inches to help get better access to the actuator. The hardest part for me was breaking the seal of the old FIPG. I had to hammer a tiny flat screwdriver into the gap (maybe not the best method but it worked). Once the actuator is off then it isn't hard to give it an overhaul on the bench.
Thanks. Solved the problem, will update post later
 
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I guess I cant edit my original post here’s how I fixed my issue

**UPDATE**

So I used the 9V battery method and I heard the actuator move and was happy about that. I cleaned the connector socket with electronic cleaner and made sure the pins will sit in nice and tight. Voila, CDL is working, both front and rear lockers are working as well! Im a happy camper to say the least! Hope this helps others troubleshoot theirs as well
 
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