Making a hidden underseat storage compartment with solenoid lock. mine uses the center seat of a Ford F 150

Step 1: Prep, Plan, Order.

Remove the existing handle on the underside of the seat. Remove the plastic tray in the compartment. set these 2 aside.(No OEM Parts were harmed in the making of this instructable) I had switch setup already. (power supply)

Ordered the solenoid (latch)
DC 12V 1.71A 6mm 700gf Actuator Door Lock Open Frame Type Solenoid https://www.amazon.com/dp/B0094FDP3Q/ref=cm_sw_r_awd_W591vbCYVR1ST
Momentary switch (trigger)
Joyluxy® QN16A1 Momentary Metal Push Button Switch 3A/250VAC 1NO SPST Industrial Car Switch with 2 Pins Suitable for 16mm 5/8" Mounting Hole - Black Shell https://www.amazon.com/dp/B00KDDAR66/ref=cm_sw_r_awd_0491vbY8ECJ6B

I already had the steel sheet for the catch and back plate peices. You should also get self tappers screws, wireing, and crimp fittings.
I removed the whole center seat assembly and did the work while it was upside-down. This made everything easier for both layout and install.

Step 2: Steel Back Plate.

Sorry no picture of plate. Back plate gives the seat a solid bottom to build from. Back part of the seat has a spot to separate the fabric for inserting the steel plate. My plate insert runs from the very front to about 4" from the rear. Mark and drill the two holes in the front where the OEM latch attached. Also add two screws on the other side securing the 2 pieces together.

Step 3: The Catch

This was the least intrusive, most secure way I could come up with for the 2 locking parts. I wanted to take up the least amount of space inside the compartment and still maintain secure lock. I using the existing cross member to mount the fabricated catch to. This provided the right amount of strength and structure. I used rivets because there are easy to use and clean. This method gives me the ability to slide the cup holder in and out. Minimizing any appearence change from outside of the compartment.

Step 4: Solenoid Latch.

Place and mark the holes, drill and attach. Be sure your not to close to the catch plate. The stroke of solenoids are different so keep this in mind. This location is only possible because we put the backplate in. I made a small slit to run the wires. I rounded the brass part to smooth operation, It was very sharp and steep out of the box.

Step 5: Wiring

Finding the best place for the momentary switch. I hid mine in an area accessible by my left hand so I lift the seat with my right. In order to open the compartment you must turn on the power and then press and hold the momentary switch. The compartment is only accessible while Pressing the button. This will keep the solenoid from overheating by leaving the power on accidentally. This also makes it more difficult to open by others. this can be done with just a switch or just a push button I choose to use both.

Step 6: Cosmetic Finishes

Paint, Carpet and finish. Paint the parts I made. I opted not to use the OEM bucket so I have to finish the inside of the compartment, but this doubles the space I have available. Work in progress.
Overall, planning how to make this work was much harder than the actual fabricating and installation.