'94 S-10 4WD problems, computer module

the 4WD does not work in my 94 blazer. I have replaced both switches (under the battery and at the transfer case). I have replace the module twice. Upon engaging the 4WD for the first time it works, then after driving for a while and trying to engage it, it will not work. The status lights will not come on either at start up. could I have a wire crossed on one of the switches?

The status lights will not come on

Do you know if the status light BULBs are good? they pull out from behind the switch to replace.
Check the vacuum actuator under the battery. Suck it in (you know , inhale) and then plug end of tube. If actuator goes back out, it is leaking and needs new one. Also check the cable between actuator and front diff.

Everything checks, the module just drops out and will not reset unless you disconnect it from the power source. You drive it for a while again and it drops out again. The switch under the battery works, that was checked first, then the switch in the transfer case was replaced, then the module dropped out. :banghead: