The trunk of my 1990 Lotus Esprit SE was stuck. The pull release was not releasing the right latch. I put in some serious troubleshooting time a few weeks ago to get it working again. Read about that adventure here. 

Unfortunately not but a week later and the trunk wouldn't open again. Initially I just ordered a new OEM latch. But that could fail just like the original. I wasn't sure if the problem was the latch or the alignment. I decided to do something more drastic. I would replace the latch assembly entirely. And if I was doing that, it sure would be nice if I could open the trunk electronically.

I checked the forums and found people that had installed solenoids to pull the cable to operate the original latch. I found people that skipped the solenoid and used linear actuators instead. In all cases though, they were using the same latch assembly I no longer trusted.

I went a different direction. I bought an "electronic rotary latch" off Amazon. These things are used on amusement park lockers. Here is the exact link. It can be opened with 12 volts, but also has two mechanical releases. Ultimately I was able to connect it up to a keyless entry system, while still allowing the original in-car manual trunk release to work, and also an emergency trunk release pull cable accessible under the car. 

Ultimately i am extremely happy with how this turned out. I have multiple ways to open my trunk, the alignment of the new latch is extremely easy and it holds tight. 

There were a couple downsides. First, you have to fabricate your own mounting brackets. No surprise there. Second, the latch opens with 12 volts but requires 12 volts for 2 full seconds of voltage to go through a complete locked to unlock to ready to lock cycle. No keyless entry system in existence provides 12 volts for that long. So you need to incorporate a timer relay that holds the voltage on for 2 seconds. Slightly more complicated and expensive, but not too bad.

Full build list

1. Electronic Rotary Latch (x2), $60 each
2. Accelle BU-509TD 30 amp adjustable time relay, $35
3. Porkchop BMX Porkvert bicycle brake cable splitter, $20
4. Generic car keyless entry system, $20

Movies

Stevens Esprit Keyless Trunk Release.mp4 (344.8MB)

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Smll Med Lrg Initially I just bought a new latch but decided to go a different route instead	Smll Med Lrg	Smll Med Lrg The new latch is well built and heavy duty. I am impressed.	Smll Med Lrg
Smll Med Lrg	Smll Med Lrg Red+Black is for unlocking. White+Blue is for checknig lock status	Smll Med Lrg Can be manually unlocked with either the left screw or the bottom lever	Smll Med Lrg
Smll Med Lrg Will replace original shaft on left with the new roller latch on right	Smll Med Lrg	Smll Med Lrg	Smll Med Lrg
Smll Med Lrg	Smll Med Lrg I ended up cutting down the sides even more	Smll Med Lrg	Smll Med Lrg
Smll Med Lrg	Smll Med Lrg	Smll Med Lrg Trimmed down the metal more. Still far more substantial than original bolt	Smll Med Lrg
Smll Med Lrg Bolt is contacting hole in body. Had to expand the hole in the body	Smll Med Lrg	Smll Med Lrg	Smll Med Lrg
Smll Med Lrg That is the depth I need	Smll Med Lrg Time to make a mounting bracket. I start with some 1	Smll Med Lrg	Smll Med Lrg
Smll Med Lrg	Smll Med Lrg	Smll Med Lrg	Smll Med Lrg This was a little on the small side. For the other latch, I made the mount longer
Smll Med Lrg	Smll Med Lrg I couldn't bend 1/8	Smll Med Lrg	Smll Med Lrg
Smll Med Lrg	Smll Med Lrg I welded some nuts on the inside of the square tube	Smll Med Lrg	Smll Med Lrg
Smll Med Lrg	Smll Med Lrg	Smll Med Lrg	Smll Med Lrg Roughly mounted in place to check the location and operation
Smll Med Lrg Bolt will need to be shortened substantially	Smll Med Lrg I welded on nuts of the same size as the OEM bolts so I could reuse the rear bolt and rubber cap	Smll Med Lrg	Smll Med Lrg I made the left bracket longer. No need for it to be short like the right side
Smll Med Lrg I decided to weld on a part so I could keep the original trunk release lever	Smll Med Lrg	Smll Med Lrg	Smll Med Lrg The nut welded on is simply to hold a bicycle cable adjuster
Smll Med Lrg The cable will pull back on the screw which manually releases the lock	Smll Med Lrg Bead blasted and ready for powder coat	Smll Med Lrg Went with Eastwood Mirror Red powder coat	Smll Med Lrg Powder coating always makes my fabricated parts look so much better
Smll Med Lrg	Smll Med Lrg	Smll Med Lrg Finally cleaned all the old grease and gunk from the body	Smll Med Lrg New latch installed in mount and ready to install on car
Smll Med Lrg	Smll Med Lrg You should make your mount longer so you don't pinch the wire I have	Smll Med Lrg	Smll Med Lrg
Smll Med Lrg I installed an SAE cable on the batter and ran it out the trunk floor. Just in case...	Smll Med Lrg I can charge the battery without openin the trunk. Unecessary but nice.	Smll Med Lrg I added a couple more leads, this time for the keyless entry I will mount on the battery	Smll Med Lrg That looks sexy. Maybe not a factory job, but certainly not ugly either
Smll Med Lrg I even powder coated the fender washers	Smll Med Lrg I can't believe how cheap keyless entry systems are now. This was only $20	Smll Med Lrg One regret, I should have found one with keyfobs with recessed buttons	Smll Med Lrg
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Smll Med Lrg My emergency release cable	Smll Med Lrg On the new latch, this lever already had a hole in it. Perfect.	Smll Med Lrg I ran the wire down and out the trunk floor. I am being overly paranoid.	Smll Med Lrg
Smll Med Lrg Oh and I changed the oil while too	Smll Med Lrg	Smll Med Lrg	Smll Med Lrg
Smll Med Lrg	Smll Med Lrg	Smll Med Lrg	Smll Med Lrg Keeping the original cable operated trunk release means splitting the cable
Smll Med Lrg This Porkchop branded bicycle cable splitter is perfect	Smll Med Lrg Original latches were spring loaded. New ones aren't. So you have to add a spring to the splitter	Smll Med Lrg I just cut some random spring that had about enough tension according to my calibrated hand	Smll Med Lrg
Smll Med Lrg	Smll Med Lrg Just cut the original cable, run into the splitter, and screw it down	Smll Med Lrg	Smll Med Lrg
Smll Med Lrg Now you get the idea	Smll Med Lrg Finding a spot to mount the splitter took me a whil	Smll Med Lrg	Smll Med Lrg I probably should have fabricated a mount for the splitter on my latch mount. Zip strip to the rescu
Smll Med Lrg	Smll Med Lrg The relay that lets the keyless entry system energize for a split second but operate the lock	Smll Med Lrg Which takes 2 full seconds for its cycle	Smll Med Lrg
Smll Med Lrg	Smll Med Lrg	Smll Med Lrg 3D printed project box to hold that mess.	Smll Med Lrg Not bad looking
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