Hi Bruce,
Welcome to the forum.
The problem could be either the relay box that you mention or a problem in the wiring between the box & the LF lamp. There are bullet connectors in the wiring which can make poor contact.
To check the box, connect a voltmeter from terminal 2 on the box to ground. It should have a green/red wire. If there is voltage, the problem is likely not the box.
As you look at the box from the RH side of the car, the terminals are numbered 1 through 4, top to bottom on the front side of the box & 5 through 8, top to bottom on the rear side of the box. If you can look closely enough, the numbers are lightly stamped on the cover.
The other lamp connections are - terminal 3, left rear, terminal 7, right rear, terminal 6, right front. Terminals 4 & 8 go to the switch on the steering wheel hub. Terminal 1 goes to the flasher relay. Terminal 5 goes to the brake lamp switch.
Yes, you can remove the cover & very carefully clean the relay contacts. This will often solve the problem.
Good luck,
D