Is the top one an older thermal design? I read in a post on at the link below that this might be an older design and I could just convert over to the newer design that I like.
1997 Chevrolet K1500 Silverado 4x4 Issues
. Ok yes that is an older thermal design. GM had issues with them and replaced them with the electronic design. You can convert it over you just need to either splice in a wire.....somewhere to the sensor above it (no 100% sure which wire yet) or buy the conversion harness at the link below...
The main problem with these older designs seem to be the problem I'm having....VERY SLOW ENGAGEMENT. Gets much worse as the outside temp drops since there is a fluid which gets heated up to allow it to expand and push what ever rod or actuator arm out to engage 4wd