Central locking question

[DoneRightBimmer]

I Know this has been covered but I search and can't figure out an answer or what steps I should take to fix.

The Issues:
So picked up a 1993 e30 325i vert recently.
1.When trying to lock the car with the key the door I am locking is the only one that locks. But when I lock both doors by hand and unlock one with the key all doors unlock.
2. Key works on both doors but when I put it into the trunk cylinder It won't turn. So I cant lock the trunk at all

What do you all recommend i should do. I read something about red black wire mod. Should I replace central locking module? Is the trunk cylinder just stuck/should I replace it?

Thanks for any help

[dnguyen1963]

Spray copious amount of WD-40 follow by some graphite powder into the trunk lock. Use your key to work the lock back and forth and you might be able to break it free.

[reelizmpro]

Check and clean the door jamb connector terminals on both doors first, then troubleshoot the central locking. Sounds as if it's okay but it's not getting a lock signal. Could be the terminals in the drivers door or a bad actuator.

[DoneRightBimmer]

Ok thanks guys I'll try those solution this weekend. Ty

[Will_NZ]

The red/back wire mod is as follows:

Remove the kick panel and speaker and get to the area where the C/L unit and connector plug to the door are. You will find 3 red/black wires in there going to the door plug. These supply power to the door lock heater in a series circuit. If you dont have a heated lock, simply cut all 3 near the plug, join all 3 together, solder and heatshrink. If you have a heated lock, just bridge all 3 together and leave the wires connected to the door plug.
The power supply through the plug accelerates corrosion of the pins, breaking the circuit. As the circuit is in series and goes into the door, to the heated lock, then back out and then to the C/L unit, any fault to the pins stops the power supply to the C/L unit, rendering it inoperable. By joining all 3 wires together, you turn the circuit into a parallel circuit.
In coupes/4door models, there are only 2 red/black wires in the loom, just join the 2 together to fix the supply problem.

[DoneRightBimmer]

Follow up on this. Ended up replacing Central Lock Module and it fixed all issues, except for the jammed up trunk lock still wont turn with key but unlocks and locks with central locking. Just posting this if someone else has a similar issue.