Introduction: Motorcycle Trunk Popper

This is one of my favourite projects that I've done so far because it arose out of genuine need to improve something, and it turned out much better than expected.

The problem I was having was that in order to remove the rear seat on my motorcycle to access the trunk, I had to use one hand to turn the key to release the latch and the other to lift the seat up. Of course whenever I'm approaching the motorcycle I have at least my helmet in hand and usually whatever I'm putting in the trunk as well. This meant that I had to put whatever I was carrying down, remove the seat and then put my stuff in.

Needless to say, this got annoying real fast and the DIY-er in me wouldn't stand for it. Here's my solution!

Step 1: Tools and Materials

So obviously this kind of project will have to be tailored to your specific application/size specifications but here's what I used:

Spring Mechanism:
* Heavy duty spring (Made from a key-ring)
* JB Weld

Latch Release Mechanism:
* Pull Solenoid (
* Standard 12V auto relay
* Fuse + fuse holder
* Momentary On push button switch
* Wiring
* Wire Tap
* Pipe Clamps

* Soldering Iron
* Multimeter
* Shop Manual for motorcycle
* Wire cutters
* Dremel

Step 2: Step 1: the Original Problem

The fix for the original problem that I had of requiring two hands to open my trunk was solved pretty easily with a simple spring. I took an ordinary keyring and stretched it out to about 3/4" long and JB welded it to the frame in a way that the seat would compress it when locked in place. This way, when I turned the key to release the latch, the seat would pop up and I could let go of the key without re-locking the seat.

Step 3: Step 2: Push-Button Unlocking

Step 1 was really simple, took about 5 minutes of work, and effectively solved my problem. However, since it was off-season and I wasn't doing any riding, I got to thinking about ways to make this fix even better. The next logical step was a button-operated electronic trunk popper.

Step 4: Step 3: Overview/ Feasibility

The first thing I do whenever I do work on my bike is consult the manual. I've worked on dozens of motorcycles and know my way around them pretty well but it's always nice to find the surprises on paper before you begin rather than when you're holding the broken pieces of your formerly working part :(

Here's a description of the exploded view of the system in question:

1. Latch end of push-pull cable
2. Seat-Lock/ Latch mechanism
3. Metal sleeve
4. Key-Lock end of push-pull cable
5. Key Lock (Original actuator for push-pull cable)

From this view It became clear that this was definitely doable. I just had to unhook the cable from the key-lock (Unhook 4 from 5) and connect it to some sort of electronic actuator. The project is a go!

Step 5: Step 4: Sourcing the Actuator

After some quick research I settled on using a pull-solenoid as my cable actuator. I'd never worked with one before so I visited to take a look what was out there and came up with the following list of specifications:

1. Must work off motorcycles 12V system
2. Must have a stroke of at least 1" (I measured the throw of my key-lock at about 3/4")
3. Must have a pulling force of at least 2 lbs (Measured by attaching a newton scale to the end of the push-pull cable and using it to open the locking mechanism)

Following these guidlines, my space limitations, and looking for something that was in stock I came up with this:

Works off 12V DC, has a stroke of 1-1/4" and according to the datasheet 3 lbs of intermittent pulling force over my required 3/4". Perfect!

Step 6: Step 5: the Mechanics

Cable Rerouting

I needed to route the push-pull cable away from the original lock to an area under my seat where I could mount the actuator. In order to run it to the desired location, I had to cut off a bit of the metal sleeve that the push pull cable sat inside (#3).

Note: The cable was still sealed inside a rubber sleeve, so I wasn't exposing the actual cable by doing this.

A couple of zip-ties later and it was in position

Mounting The Solenoid

The first part of this involved connecting the end of the cable to the solenoid's core (the cylinder in the solenoid that moves). I did this by boring out the already existing hole at the end of it and cutting a small slot into the hole through which to slide the cable (see picture for a better idea).

The second part was securing the solenoid housing to the bike.To do this, I strapped the solenoid to my frame using some zip ties and moved it around until it the cable was nice and taught but not engaged. At this point, with everything attached, I did my first test run by touching the solenoids wires to my battery for a moment. Success!
I then replaced the zip ties with two stainless steel hose clamps and welded the clamps to my subframe. This way the solenoid is very secure but can easily be removed by loosening the clamps.

Step 7: Step 6: Electronics

With all the mechanical stuff taken care of, all that was left to do was to hook up the solenoid to the battery.

The Relay
I couldn't wire the solenoid straight to the battery because this would mean that it could be activated at any time so any passer-by could open my trunk. To take care of this problem I used a standard 12V automotive relay triggered off a switched line (see description below for more details). I once again consulted my repair manual and ended up tapping into the license plate light line to switch the relay. This way when the ignition is turned on, my solenoid will work but without the key in the ignition it will not.

A relay is like a switch that is turned on-off by an electrical signal. Essentially it allows you to turn a device that draws a lot of current on/off with a low current line. If you look at my diagram you can see that when 12V is applied over terminals 1&3 (low current from switched line) then terminals 2 and 5 are connected (high current from battery). However when apply 0V across 1&3 then 2 is connected to 4.

In this case my wiring was as follows:
1- Tapped into license plate light positive (12V)
3- Tapped into license plate light negative (ground)
2- Battery positive terminal
5- To solenoid

The Fuse
I opted to use a simple in line fuse holder with a 10A fuse just in case something shorted or somehow my switch got stuck in the on position I didn't want any wires melting.

The Switch
To activate my solenoid I used a basic momentary-on push button switch that I hid on the underside of my tail.

See the wiring diagram below for details

Step 8: Finished Product

And finally, here is the finished product. From two hands to single finger trunk opening :)

I hope you enjoyed my instructable, keep innovating!

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