Delica Canada | Mitsubishi Van Club

This may be the circuit for the door. It makes sense to me. I think the driver's door controls everything. I haven't had it all apart but have used it for remote access. The physical movement of the lever must reverse voltage to provide the 2 directions.

I have this issue as well. More like central locking gremlins. I'll open the drivers door, sometimes the passenger and sliding door will unlock sometimes not. Then I'll be driving a minute later and they will unlock.

I'm pretty sure my issue is attributed to the lock relay located above the main fuse box. I've had water get into the van and run down the fuse box causing a short in the past. So I assume my lock relay is getting corroded and causing the central locks to work intermittently.

As per LRP374 there is a fuse above the battery which I'm gonna pull and check to see if there is corrosion, etc.

From what I can tell some are Blue/Red and the others are Red/Blue with a black ground. I have a larger diagram I could scan if that would help.

That's the door locking circuit for European vans, where the sliding door and tailgate are both controlled by the "door lock" switch on the dashboard.

Here's a circuit that's closer to ours: it's for Australian model vans. The difference is that Aussie models have a motor and switch in each front door (so you can lock/unlock from either side), but ours only have a switch on the drivers side and no motor (and no switch on the passenger side). The switch is, as you said in your original post, a single pole switch connected to earth- if it closes, the control unit unlocks the doors. If it opens, the unit locks the doors. Or maybe the other way round.

Note that "CENTER DOOR LOCKING SWITCH" is misleading, that's the tailgate switch.
Looking at the diagram and considering the fault (only locks) I'd say you either have a faulty control unit or the 'unlock' half of the relay is burnt out.

(Door lock relay wire colours, left->right

Brown/White
Black
Large Blue/Black
Blue/Red
Blue/Red
Blue/Red
Large Blue/Red
Black
Brown/Blue)

I had the dash out the other day, and my central locking relay is a nightmare to get to- It's relatively low on the front panel, directly behind the brake booster. I confirmed its function by touching it while locking and unlocking the doors- you can feel it click.

If that's where yours is, I suspect you'll have to remove the dashboard crossmember, brake booster, and pedal box to get to it. They're not particularly difficult to remove, but it's irritating. You might be able to unbolt the brake master cylinder from the booster and leave it dangling by the brake lines, which will avoid having to bleed the brakes.

The control unit is to the right of the relay, and I could *just* reach it.

If I ever remove the pedal box, I'll be opening up the wiring loom and moving the relay to the right, where I can get at it more easily.