Airbag Recall/ Light On

So a few years ago I got the letter for an airbag recall. I took it into the dealer, had it fixed, in and out.
After a while . . . a year or so, the airbag light came on. I left it, turned the passenger side to 'off' with the key and ignored it.
Then I get ANOTHER airbag recall letter. I'm guessing the part they replaced the original with was bad as well.
So I just got back from dropping it off at the dealer and the service writer says to me, "You know your airbag light is on right"? I said, "Yes, I figured that's the reason I got the airbag recall letter". He said, "That 'MAY' be the case but it might not be associated with the recall portion at all". He then says that it'll cost me $150 to diagnose why the light is on. I said no thanks.
Anyone have any experience with this? The truck has never been in an accident, (if that makes any difference). Nothing I've seen or done would indicate why the light would be on.