Hello, I have 99 chevy blazer and the front wheels will not engage when put in 4wd. I have 3 button 4wd. When I push the 4hi or 4lo button the light comes on and stays on but the front wheels do not engage. Can anyone help me please.

With the engine at idle in park, and 4WD selected, make sure there is vacuum applied to the actuator under the battery and that the cable pulls in about 3/4" and then releases immediately when you select 2WD.

I removed the battery today and look for that actuator and did not see it. Could you tell me if I stand in front of the truch with battery removed where it is. Also if I may ask you one more question, does that actuator have a 2 prong plug and 2 vacum line connectors.

The vacuum actuator in under the battery tray, there is one vacuum line attached to it.

ok, so I have the wrong actuator. I need the round one.

This is what it looks like:
http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product_4WD-Actuator-Dorman_17191001-P_2108_R%7CGRPSESWAMS____