1998 Dodge Ram 1500 four wheel drive won't engage.?

you probably do have a vacuum leak on it,you need to find the sticker in the front under the hood and trace the hoses out and you,ll find the one that has came loose.you more than likely accidentally knocked them loose while working on it ,don't worry though its a simple repair,follow the ones back from the actuator and that's a good starting point to find the loose one on it,good luck.