If your '99 has a '99 built chassis, you have an OBDII port. By regulation, they must be 2 ft from the drivers seat. On a Ford,they are attached to the right side of the steering column about half way up from the floor. Yours should be very similar.
I had a hellava time finding mine even though I knew where it was suppose to be. The doghouse, being 6 ft and 230lbs, not much light and everything under there being black made it difficult.
John & Clare Lyon
2007 43.5' Monaco Dynasty Palace III (All Electric)
Towd: 2011 Chevy Equinox