I can’t find any sign of an OBD2 port and have an airbag light on.
Can anyone tell me if the car (1999 Riviera) has an OBD2 port
and if not, what is the most likely cause of the airbag light staying on?
Thanks

Most common reason for light coming on is disturbance of the yellow cable and connector under the seats. Only needs a slight knock to do it. The OBD2 port on my B is under a plastic flap in the front of the cross beam below the driver's seat.

Earlier models like yours and mine don't have an obd 2 port, but you can access diagnostic and reset with an adaptor and multiscanecu they are three pin ports the airbag one is usually under the passenger dash,at the end of a bright yellow cable.

Always disconnect the battery before unplugging anything. The common cause for airbag light is unplugging wires under drivers seat with battery still connected.

You cannot reset airbag light with Multiecuscan, as far as I know. To do this, you will need trw2scan:
https://www.fiatforum.com/barchetta/326382-air-back-alarm-light-after-seat-removal-2.html?p=3277005

Your car probably doesnt have a OBD2 port, instead it will have 3 x 3 pin connectors, each serves a different purpose. Their probable locations are:

Air-bag control unit = Under the passengers glove box.
Brake servo unit = Next to the brake reservoir
ECU = Behind the inlet manifold under a plastic cover, mounted to the firewall

Each plug will be sheafed inside a plastic cover. Simply take the plug out of the cover to use it.

To connect to the ECU/air-bag control unit, you'll need to do the following:

1) Get a laptop
2) Install multi-ecu-scan (https://www.multiecuscan.net/)
3) Buy a 3 pin to OBD2 connector
4) Buy a VAG KKL Multiecuscan adaptor

Then plug the 3 pin into the connector, the VAG KKL adapter to the OBD2 connector and VAG KKL adapter connect it to the battery.

When connecting to the air-bag unit I used jumper cables to connect the VAG KKL adapter to the battery.

minimayhem said:

Brake servo unit = Next to the brake reservoir

Click to expand...

Only useful on 1997+ cars with Bosch-ABS 5.3. Older ABS 2SH version cannot be read by MES.

minimayhem said:

ECU = Behind the inlet manifold under a plastic cover, mounted to the firewall

Click to expand...

On my 1996 years car there is an extension cable from this place to the passenger footwell, with 3-pin plug on the right side of the footwell behind the trim.

Useful to know!

If we compile everything about where to find the 3 pin plugs and OBD2 connector on all years, this will be the thread to go to for all future forum users with the same question