Diff Lock Lights Weird Behavior

[DARKNESS]

My front and rear diff lock lights are stuck on. This has been slowly coming on for awhile. They would initially come on when turned the key then they would turn off progressively more slowly until finally they were stuck on. However they are not fully bright. They seem oscillate in brightness with movement of the vehicle. If I move slowly, they pulse slowly and vice versa. Also, if I use the turn signal they pulse with the blinker.

If I turn the diff lock switch, the lights go off. If I push the center diff lock switch, the lights go off, but the CDL light does not go on regardless of whether I'm in low or not. I can hear clicking in the center diff relay but it doesn't seem like the diff is trying to lock.

If I unplug the diff lock ECU the lights go out. I have shorted the pins for the front, rear, and center diff lock bulbs to ground and all the bulbs work. I tried replacing the capacitors in the diff lock ECU since those can go bad with age, and got no change. Also tested the diff lock switch and its fine. I also unplugged the front, center and rear diff lock sensors and got no change.

I'm at a bit of a loss. Nothing I can see in the EWD should be able to cause these problems except the ECU. Unfortunately they're $$$ if they're even available, so I'd rather not go down that road unless I have no other option. Anyone got any ideas?

 

[jonheld]

My front and rear diff lock lights are stuck on. This has been slowly coming on for awhile. They would initially come on when turned the key then they would turn off progressively more slowly until finally they were stuck on. However they are not fully bright. They seem oscillate in brightness with movement of the vehicle. If I move slowly, they pulse slowly and vice versa. Also, if I use the turn signal they pulse with the blinker.

If I turn the diff lock switch, the lights go off. If I push the center diff lock switch, the lights go off, but the CDL light does not go on regardless of whether I'm in low or not. I can hear clicking in the center diff relay but it doesn't seem like the diff is trying to lock.

If I unplug the diff lock ECU the lights go out. I have shorted the pins for the front, rear, and center diff lock bulbs to ground and all the bulbs work. I tried replacing the capacitors in the diff lock ECU since those can go bad with age, and got no change. Also tested the diff lock switch and its fine. I also unplugged the front, center and rear diff lock sensors and got no change.

I'm at a bit of a loss. Nothing I can see in the EWD should be able to cause these problems except the ECU. Unfortunately they're $$$ if they're even available, so I'd rather not go down that road unless I have no other option. Anyone got any ideas?

The F/R diff lock dash lamps are illuminated by the ground path through the switches on each diff. However, that is only when they're fully locked and the associated switches are closed.
When they are either locking or unlocking, the lamps pulse by the ECU grounding pins 2 (rear) and 9 (front).
If you have unplugged the front and rear switches and the lamps are still illuminated, then the only ground path that remains is the diff lock ECU.

 

[DARKNESS]

Thanks! That's how I interpreted it as well but wanted to be sure I wasn't missing anything.

 

[DARKNESS]

I tried unplugging the Diff Lock ECU and the center differential still isn't working, so I'll try to tackle that first.

 

[jonheld]

I tried unplugging the Diff Lock ECU and the center differential still isn't working, so I'll try to tackle that first.

The F/R diff locks don't have any control over the CDL. That's completely dependent on the low range switch in the stock configuration, or the CDL dash switch with the pin 7 modification.
In the stock configuration, the F/R diff locks will not engage without the CDL locked. That can also be modified by grounding pin 15 on the diff lock ECU, but that's another topic.