Power door lock relay location

When used, there has to be two power lock relays, but your car doesn't need or use them. All switching is done with the door switches.

I can't find a wiring diagram online, so it's harder to explain, but when only the lock or unlock function doesn't work, and only from one switch, either switch can be the cause. There's actually four sets of contacts in each switch. Two in each are in the circuit for "unlock", and the other two in each switch are in the circuit for "lock". Fifty percent of the time the properly-working switch is the one with the burned or pitted contact.

Being a safety-related system, the circuit is usually protected with an auto-resetting thermal circuit breaker. I had two '78 LeBarons, and as I recall, those used glass fuses. I didn't have power locks, so I don't remember if they used fuses or circuit breakers back then. The fuses were labelled with small black lettering, so check for a fuse first and see if it's blown.

Probably the most common failure with this system is broken wires between the door hinges. Check for that first. If you find that, I'll describe how I do that repair.