Add remote locks to an E30 for about $15

Add a keyless remote to your E30's central locking for about the price of a pizza, in roughly fifteen minutes. A cheap universal lock kit plugs into the wires the factory central locking already uses, so the car's own locking system does the work. This version is lock and unlock only, mounted in the boot, and it needs no drilling and no changes to the dash.

What you need

Parts

• A universal remote lock kit with a control unit, two remotes and a wiring lead, such as this one: universal remote lock kit on Amazon. A kit like this cost about $15 when I first did this, and prices vary.
• A few feet of spare wire, for the power connection.
• Heat-shrink tubing, and tape to wrap the finished wiring.
• Double-sided mounting tape, to fix the control unit.

Tools

• Soldering iron and solder (or wire splice connectors, if you prefer)
• Wire cutters and strippers
• A test light or multimeter, to confirm which wires are which

As an Amazon Associate I earn from qualifying purchases. It does not cost you extra.

How it works

The E30's central locking is run by a control unit that locks and unlocks every door when it receives a signal on its lock or unlock wire. The lock switch in the driver's door sends that signal when you turn the key or press the button. A remote kit simply sends the same signal from a receiver you hide in the boot.

Fitting it at the boot end of the wiring is the easiest option. The wires you need run under the carpet between the tail lights, and they are easy to reach. Wiring a kit in under the dash would also let it flash the hazard lights, chirp on lock or sound the horn, but this version leaves all of that out on purpose, so there is less to wire and less to go wrong.

Step by step

Check your kit's wires. These steps use the wire colours of the kit I fitted. Different brands colour their leads differently. If yours does not match, use the instructions that came with it to find its lock, unlock, ground and 12 V power wires, and make the same connections. The kits that include a trunk release button have extra wires for it, which you can leave unused.

1. Remove both tail light covers inside the boot, so you can get at the wiring behind them.
2. Pull out the carpet panel that sits between the tail lights.
3. Draw out the wire bundle behind the centre piece, and unwrap a short section of the tape around it so you can see the individual wires.
4. Pick out the three car wires you need: green/black, green/purple and brown. Cut each one, and strip the ends.
5. Strip the six lock kit wires you will use: white, white/black, orange, orange/black, black and red. The kit has others, but you will not need them, so tuck them away.
6. Join the ground side. Solder both orange wires and the black lock wire to the brown car wire, and cover each joint with heat-shrink.
7. Join the black/white lock wire to the green/purple car wire. Solder it and heat-shrink the joint.
8. Join the white lock wire to the green/black car wire. Solder it and heat-shrink the joint.
9. Connect 12 volts. The red wire needs a permanent 12 V supply. I tapped it into the red wire at the antenna. On a car with a power antenna that wire carries constant 12 V on fuse 28 (30 A), which it shares with the cigar lighter. You can also run a wire to the battery instead, with an in-line fuse close to the battery.
10. Mount the control unit to the wall of the boot with double-sided tape, where it will stay dry and out of the way.
11. Wrap the wiring in tape so it stays neat and does not rattle or shift.
12. Reconnect the battery and test before you refit anything (see the next section).
13. Refit the carpet panel and the tail light covers.

Soldering gives the neatest, most reliable joints, and it is the way I did it. Wire splice connectors are faster, and they are fine if you crimp them properly. Twisting wires together and taping them is not a repair. See the harness repair guide for how to make a good joint.

Testing it

1. Reconnect the battery. With a door shut and the key out, press lock on the remote. All the doors should lock.
2. Press unlock. All the doors should unlock.
3. If lock and unlock are the wrong way round, swap the white and the black/white lock wires on the car side. That simply reverses which button does which.
4. If the kit needs its remotes pairing to the receiver, follow the instructions that came with it.
5. Once everything works, secure the wiring, then refit the trim.

If it does not work

Wire colours vary by year

The wire colours in the steps are the ones on the car I fitted. BMW changed some colours over the E30's life, so check yours before you cut. The 1987 factory manual, for instance, shows the boot lid lock motor's lock and unlock signals on green/black and yellow/black wires, not the green/purple ones above. The ground is brown in both. Confirm the two signal wires with a test light or meter, and compare them with the wiring pages: central locking control (4 door) for the boot wires, and central locking, 4 door or 2 door for the rest.

Do not join the kit to a wire you have not identified. If you are not sure, trace the wire to the central locking control unit and match it to the lock and unlock inputs on the wiring pages before you cut anything.

Written from the factory wiring diagrams on this site and general diagnostic practice. Voltages, resistances and pressures are typical figures, so confirm them against your car's manual. Take care with fuel, high voltage and the battery.