Remote RF Control For Rear Hatch?

[OK-944]

I’m thinking that it would be pretty nice, as I approach my car with an armload/basketload of groceries or other items, to simply press a remote switch to activate my car’s electric hatch lift switch.

Also, as a photographer using some pretty expensive gear, I really don’t like having to put this stuff on the ground in a dirty/wet parking lot in order to open the hatch manually.

Plus, no matter that I've cleaned and lubed my hatch pin receiver plates, the effort required to turn the key to open the hatch manually still has me thinking that its only a matter of time before the key starts to bend and perhaps break.

Seems like it should be really simple to graft a remote (RF) momentary switch into the rear hatch circuit. Lots of inexpensive kits available online, in key-fob form. Has anyone here done this?

[944 Ecology]

If you wire a remote momentary into the circuit for the hatch release motor, should work just fine. Just be careful with the amount of parasitic draw from the receiver.

Make sure you document the installation for the next owner.

[originalowner]

It's not quite easy, you can't just parallel the remote with the switch. This is because the switch also handles part of the motor braking function, which shorts the windings when the motor gets to the stop position. You'd need to change out the existing switch for a SPDT relay, then activate the relay with the the switch and remote in parallel.

[onZedge]

I've actually been working on a wiring diagram to add keyless entry to my 924S. Here is a snippet of the circuit for connecting the keyless entry controller to the hatch button circuit, with an interposing relay (added in blue). The brown wire is momentarily grounded to energize the circuit (via an auxiliary output on the keyless entry controller), similar to pushing the button. Note that this piggy backs on the existing without defeating the manual pushbutton.

[OK-944]

This is exactly what I was thinking...to piggyback into the existing circuit so the car's existing pushbutton would still function as usual.

I'm not great with these electrical diagrams (even though I've wired a house), but I think it will eventually make sense.

There are a number of RF switch units on the market...and my assumption is that I'd want something which will work with 12 volts...but what about amps? Many units are rated at 10 amps, which I assume would be sufficient...although maybe I'll look at the fuse for this circuit to verify this.

At any rate...thanks for the diagram!

[originalowner]

The circuit is fused at 25A for both old and new cars. I don't know what that motor actually draws though.

[originalowner]

In the older cars, the fuse is shared with the fresh air blower (heater blower.) In thinking about this today, your could turn off the blower, swap the fuse out with an 8 amp version, and pop the hatch and keep the release running for a bit to see if the fuse holds. It's going to draw maximum current while trying to release the hatch since there is additional friction in the release mechanism when it is closed. This would be a clue that a 10amp relay might work.

They make SPDT remote relay modules. This could be used as the relay in the above diagram, provided it can handle the current. There would be no need to for anything additional to make or break the ground.

[originalowner]

Shower thought: You might want to add a relay to kill power to the remote module while the ignition is on. I don't know how good a cheap Ebay module is at spurious signal rejection, or other possible engineering concerns. Popping the hatch at speed would be "interesting."

[OK-944]

Hmmm...sounds like a good idea!

[944 Ecology]

So, just for giggles, I did a test on my 86 951 (should be the same as your 84) with my power probe (a great tool, check it out) and, with a momentary pulse to pin 53 (red wire with a white stripe) at the red connector near the hatch release motor, I was able to make it cycle one time, accomplishing the unlocking. Judging by the diameter of those wire, probably 5 amps or less.

I'm going to order an amazon remote switch, just to check it out. Probably worth $15 for the fun and additional knowledge. Will post more later.

[9FF]

You know what would be cool. Replace the hatch struts with linear actuators and get rid of the pins completely.

[944 Ecology]

Amazon screwed up the order... project put on hold, but definitely doable and simple to tap into the wiring for the motor connector.

I may consider doing it in the spring/summer.

[OK-944]

Too bad about the Amazon order...but I'm also thinking that this would make a good springtime project.

I'm guessing that the mechanism would be the same on my '87 as on your 86 951, and that grafting in the remote switch near the hatch motor would make sense. It also sounds like the existing cabin switch would still work.

At any rate...in the meantime - I will check out one of those power probes, and if I decide to jump into this project before spring...I'll post some results, but otherwise, I'll look forward to knowing how yours has worked out.

[originalowner]

Amazon dropped the ball on my order too. Shame. I've got an Aliexpress order in, so maybe in a month or two.

[OK-944]

Jeeesh...looks like I need to get with my own program and order some parts!

Which one(s) did you guys order, by the way?

[originalowner]

Amazon calls it: QIACHIP DC 12V 1CH 433Mhz RF Wireless Relay Remote Control Light Momentary Switch Transmitter with Receiver (1relays)

[originalowner]

Originally Posted by OK-944

that grafting in the remote switch near the hatch motor would make sense.

I'm all about the safety of disabling the remote with a relay with the ignition on. I was originally thinking that there is no ignition signal at the rear, but I eventually realized you might be able to route the fuel pump power into the cabin somehow in order to disable the remote. Fuel pump not running would be a reasonable proxy for the car not moving, and being able to safely pop the hatch.

I'll probably mount mine near the switch since the ignition on signal is available nearby.

[944 Ecology]

Got my Amazon remote relay... pretty spiffy for $10. Bench tested it with a 12 v power supply and a VOM to check for load switching, and it is surprisingly robust. All I need to do now is tap into three wires at the motor and watch the magic happen!

[OK-944]

George...please keep us posted!

BTW - which unit did you purchase from Amazon?

I do wonder about Mr. Original's concern about RF interference. Would hate to be cruising down the highway and suddenly have the hatch opening up or at least flapping in the wind!

At any rate...good luck!

[944 Ecology]

Originally Posted by OK-944

George...please keep us posted!

BTW - which unit did you purchase from Amazon?

I do wonder about Mr. Original's concern about RF interference. Would hate to be cruising down the highway and suddenly have the hatch opening up or at least flapping in the wind!

At any rate...good luck!

I got the one that originalowner identified in a prior post.

I scanned in the instructions and highlighted the pertinent sections for the 944 hatch. You can download the pdf here:

https://drive.google.com/file/d/1uvK3RuZzRnFWjlJNK8OyC9iJYLyuHM9_/view?usp=sharing

I'm not too concerned about the rear hatch becoming unlocked while driving. The hatch is not designed to raise up by itself, that only happens in the case where the hatch shocks are too strong (that's only one of the problems, the glass delaminating from the frame is the more serious consequence of too strong hatch shocks.)