power lock issues?

[Low Elco]

Bought an 87 swb gmc that's hard loaded, and as usual, most of it's on the blink. When you hit the power locks, a black box under the dash by the gas pedal clicks, and nothing happens at the doors. Anyone know anything about these?

[J Knight]

90% of the time when the widows or door locks dont work its either the switch or the motor/actuator. Its always possible it could be a broken wire or a burned plug.

[turner16]

the noise is the relay. If it is a wire issue it will be where it goes through the doors.
I would check the back of the switches first.

[motornut]

my 88 had issues with the windows/locks when i bought it
found cracks in the wires in the drivers door tube
that and no motors were ever put in the back doors lol is a big one
changed to manual cranks,was going to take powers out of the 89 but didn't

[ges55]

Since the relay is clicking, your switches are probably ok. You can get the actuators on Ebay. I got 2 for $50. If your switches aren't making the relay click in both up & down modes, you can pop them out, pry them apart & clean them out & alot of the time that will make them work. Also, sometimes there are rust issues in the actuator linkage that can cause the actuator to not work & that can be fixed by removing the door panel & spraying lubricant on the rusty area. Just follow the linkage down from the lock button. Good luck.