1999 GMC Jimmy will not engage 4 wd

I INSTALLED A NEW TRANSFER CASE MOTOR
THE LIGHTS ON THE DASH MOUNTED SWITCH LIGHT UP WHEN I TURN THE KEY ON AND THE 2 WD LIGHT STAYS ON HOWEVER WHEN I PRESS 4 HI OR ANY OF THE OTHER BUTTONS NOTHING HAPPENS. WHEN THE TRUCK WARMS UP IT WILL GO INTO 4 LO AND THATS IT I HAVE TO PRESS 2 WD SEVERAL TIMES TO GET IT OUT OF 4 LO WHAT CAN BE THE PROBLEM?