It's also possible that it's engaging, but the sensor is not making contact, which will prevent the diff lock and ABS lights from coming on. Have you tried it on a higher traction surface to see if the driveline binds up?
I used one of these on a trip from TX to CA http://www.amazon.com/dp/B007WR25DY/?tag=ihco-20 Drove through a couple of moderate rainstorms and everything stayed dry. Also had a 15 gal Action Packer, which did not get any water inside. The Action Packer is lockable, although you need two locks...
FWIW, I will throw in my data to add to the mix. We drove into San Diego from Tucson yesterday on I-8.
Current truck setup
1995 w/ SC 200k mi
35s, 4:56 gears, ARB bumper w/warn 12k winch, TJM rear bumper w/ tire carrier
94 3-core brass rad
Blue hub fan clutch w/10k fluid
Good news... New axle seal installed and truck is ready to roll on to CA. Repair was handled by Derrick at The Shop, a small repair shop here in Benson, AZ. Great guy! In addition to the repair, he brought me back to the motel and picked me up when the truck was ready. He is a great resource if...
Monday status update... Picked up new seals from O'Reillys this morning and delivered them and the truck to a local guy here in Benson, who is going to install them this afternoon. If all goes well, we should be back on the road in the morning.
Thanks, I appreciate it. Good thought about the rental, but since we're going to be in CA for a month, so renting would be an expensive option.
If the local Benson guy can't do it, I'll call the guys at Douglas. I'm just trying to avoid the drive as the axle is losing a lot of oil and I expect...