Can I bypass the electric/vacuum solenoid that engages the four wheel drive unit
 

Hi guys. I bought a 98 Isuzu trooper that needs the electric/vacuum solenoid that engages the four wheel drive unit.. They're proving almost impossible to find good ones in a junkyard and I'd rather not pay $200+/-
If I can avoid it. Can they be bypassed and have the four wheel drive unit work?? Just trying to find a quick fix to get thru this winter then I'll probably upgrade to something newer...
Thanks in advance JD