I just finished changing the oil pan on my truck (which turned out being more hassle than I had counted on) and now when I startmy truck the check engine light comes on. I'm thinking maybe I have the vacuum lines reversed but I'm looking for other ideas?

 

Check Engine Lights almost always indicate something is wrong with the emissions system, which aside from the cat(s), operates on vaccum.

So more than likely you have vaccum hoses mis-routed. Its VERY easy to do,done that many times.

If you re-check everything and have no luck, your local service station has a scan tool that can "read the codes" which cause the check engine light to come on. Its very possible while you were working on your engine, you bumped a connector that was loose to begin with, and a sensor is not connected properly. Been there done that too.

 

What year is the truck? If it's older than '96, you can pull the codes yourself.

http://fordfuelinjection.com/index.htm

Click on "Getting Codes" on the left side of the screen. It also provides code definitions when you get them.

If it's '96 or newer truck, go to autozone, they will pull the codes for free.

 

Did you have to unplug the O2 sensor to get the pipe out of the way? If so, did you plug it back in?