Seatbelt light comes on with Headlights

The only time my seat belt light comes on is when the Headlights are on. It is a 67 standard 6.5. Has what I believe are 68 seats in it. Has seatback lock. How do I get it to go off or work correctly.

Someone has swapped the instrument backlighting bulb socket for the seatbelt bulb socket. Swap that for starters. Likely the seatbelt relay is unplugged, and / or the bulb is burned out on the seatbelt lamp. The instrument backlighting bulb sockets each have a baby blue wire with a red stripe leading to them.

Thank You Royce, I will check that out.