This is an extremely easy job to undertake on the 240, every wire is color-coded for clarity and *should* match up to your alarm brain. This guide specifically references the Audiovox Prestige AA925 BGAAL10R Brain, which can be found on eBay for ~$35 shipped. Your brain may differ, please reference your instruction manual regarding wiring.
Door Solenoid:
First order of business is installing a solenoid into the drivers' door. You don't want a remote that opens up EVERY door except the drivers' door, do you? I didn't think so. Pick up a solenoid from any other door/hatch from another 240. The bracket on the solenoid flips around so that the same unit can be used in ANY location.
Here's what it looks like installed:
Next up is making the linkage so that the solenoid works the locks. I used a wire hangar for this, but if you're at the junkyard scavenging solenoids, grab the rods as well. I had a solenoid from a tailgate but no link rods, so I had to improvise. When you're done, it should look something like this:
Because I didn't have the stock linkage rods, I had to drill a hole in this piece:
This works fairly well but I'd like to strongly reiterate that it would be MUCH easier to use the linkage rods that volvo supplies. EDIT: the front passenger door linkage works great here. It's not perfect but it's MUCH easier than drilling and bending coat hangar rod.
Next up, wiring. The door solenoid has blue and yellow wires. If you look at the wires coming from the key and lock pin switches, they are ALSO blue and yellow. However, you can't use these because they are signal lines to the relays, not the actuation lines. So you'll have to extend the wires from the solenoid into the cabin and behind the middle heater vents (where the relays reside).
I ran mine along the inner door harness and fished them through above the fuse box, like so:
Wiring the Alarm Brain:
The Volvo 240 is a negative (-) pulse lock and unlock system. The relays for the door locks are located behind the center console, up behind where the coin tray would be and almost right underneath the vents. #188 and #189 in this picture:
After you fish those out, find the wire sheath that brings a green and a red wire to the relays. These are your signal wires. Connect your negative unlock pulse wire to the green, and the negative lock pulse wire to the red. IMPORTANT! If you connect your signal wires from your brain to the WRONG wires, you WILL FRY YOUR ALARM BRAIN. See wiring diagram below - there's another green wire that supplies 12v constant to both relays, do NOT connect your signal lines to this wire!
Then find the blue and yellow wires going from the relays into another sheath and connect the wires from your drivers' door solenoid.
Here's a modified greenbook diagram:
After everything is connected, you should be done! Wasn't that easy?!? For less than $50 including the JY cost of the solenoid/rods and alarm, you now have keyless entry. Enjoy!
Door Solenoid:
First order of business is installing a solenoid into the drivers' door. You don't want a remote that opens up EVERY door except the drivers' door, do you? I didn't think so. Pick up a solenoid from any other door/hatch from another 240. The bracket on the solenoid flips around so that the same unit can be used in ANY location.
Here's what it looks like installed:

Next up is making the linkage so that the solenoid works the locks. I used a wire hangar for this, but if you're at the junkyard scavenging solenoids, grab the rods as well. I had a solenoid from a tailgate but no link rods, so I had to improvise. When you're done, it should look something like this:


Because I didn't have the stock linkage rods, I had to drill a hole in this piece:

This works fairly well but I'd like to strongly reiterate that it would be MUCH easier to use the linkage rods that volvo supplies. EDIT: the front passenger door linkage works great here. It's not perfect but it's MUCH easier than drilling and bending coat hangar rod.
Next up, wiring. The door solenoid has blue and yellow wires. If you look at the wires coming from the key and lock pin switches, they are ALSO blue and yellow. However, you can't use these because they are signal lines to the relays, not the actuation lines. So you'll have to extend the wires from the solenoid into the cabin and behind the middle heater vents (where the relays reside).
I ran mine along the inner door harness and fished them through above the fuse box, like so:


Wiring the Alarm Brain:
The Volvo 240 is a negative (-) pulse lock and unlock system. The relays for the door locks are located behind the center console, up behind where the coin tray would be and almost right underneath the vents. #188 and #189 in this picture:

After you fish those out, find the wire sheath that brings a green and a red wire to the relays. These are your signal wires. Connect your negative unlock pulse wire to the green, and the negative lock pulse wire to the red. IMPORTANT! If you connect your signal wires from your brain to the WRONG wires, you WILL FRY YOUR ALARM BRAIN. See wiring diagram below - there's another green wire that supplies 12v constant to both relays, do NOT connect your signal lines to this wire!
Then find the blue and yellow wires going from the relays into another sheath and connect the wires from your drivers' door solenoid.
Here's a modified greenbook diagram:

After everything is connected, you should be done! Wasn't that easy?!? For less than $50 including the JY cost of the solenoid/rods and alarm, you now have keyless entry. Enjoy!
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