Hi all,

I am in the process of going over the electrical system of an old car. It's a 2 door with a rear tailgate/hatch/trunk. I'm adding aftermarket central locking which is 2x 5 wire solenoids with a control module. Just the generic type you buy from Amazon or the auto shop. I'm also changing the tailgate from mechanical opening to a solenoid that 'pops' it open. There will be no mechanical lever to open the tailgate only the solenoid moving the levers and linkages inside, controlled by a relay and switches. I will be adding an alarm system that controls the door locking and unlocking via a brown and white wire on the central locking control module and also controlling the relay that powers the tailgate opening solenoid for 'boot/trunk release' from the remote. The tailgate solenoid will be powered through a regular automotive 4/5 pin relay that I will control via a button on the outside of the tailgate, a button in the glovebox and the alarms 'boot/trunk release' wire. All works expect....

The problem is that one of the switches will be a button on the outside of the vehicle to open the tailgate which is an obvious security problem when the car is locked. I would like to disable the outside button when the vehicle is locked. The other consideration is I would like whatever method I use to only consume power when changing states from active to not active but not consume power when idle in either state. IE: I can leave the car locked or unlocked in the garage and the system is not slowly draining the battery.

I have done this with a 2 wire door lock solenoid connected to an unused rear door connection on the central locking module. I have a frame to hold the solenoid and a micro switch so the solenoid presses on the microswitch or release so I can open and close the tailgate open button circuit. It works but feels a bit unnecessary when surely there must be an electronic way to do the same.

I purchased and was hoping to be able to use this latching relay from Ali and connect the set and reset pins to the brown and white lock and unlock wires of the central locking module. The latching relay load would be the tailgate button circuit which the latching relay would create an open circuit when the car is locked and close the circuit when the car is unlocked so the button would work when unlocked but not work when locked. I have tested this and it works but because the brown or white wire holds the connection to ground, about 65mA continues to flow through the coil after the latching relay switches. I would prefer no power consumption and I don't think the relay is designed to have constant power through the coil. Only a ground pulse to each coil to change the state.

The brown and white wires from the central locking module appear to be a ground source for their state IE Brown is ground when locked and White is ground when unlocked but I'm not certain of that because if I ground each wire separately to central locking system locks and unlocks.

So, I guess I am looking for a circuit or 2 individual circuits that uses the ground on brown or white to then pulse a ground to the set pin (or reset pin) on the latching relay but not use any power while idle.

I was looking at this post where the user is looking for a ground pulse but the situation looks to be a bit different.

Or maybe I am looking at it all wrong and there is a simpler solution?

Does anyone have suggestion how I can work with what I have to disable the outside tailgate opening button when the vehicle is locked?

Hope all of that makes sense, I enjoy little electrical/electronic projects but am not always sure of correct language to use when describing things.

Thanks.

 

Hi all,

I am in the process of going over the electrical system of an old car. It's a 2 door with a rear tailgate/hatch/trunk. I'm adding aftermarket central locking which is 2x 5 wire solenoids with a control module. Just the generic type you buy from Amazon or the auto shop. I'm also changing the tailgate from mechanical opening to a solenoid that 'pops' it open. There will be no mechanical lever to open the tailgate only the solenoid moving the levers and linkages inside, controlled by a relay and switches. I will be adding an alarm system that controls the door locking and unlocking via a brown and white wire on the central locking control module and also controlling the relay that powers the tailgate opening solenoid for 'boot/trunk release' from the remote. The tailgate solenoid will be powered through a regular automotive 4/5 pin relay that I will control via a button on the outside of the tailgate, a button in the glovebox and the alarms 'boot/trunk release' wire. All works expect....

The problem is that one of the switches will be a button on the outside of the vehicle to open the tailgate which is an obvious security problem when the car is locked. I would like to disable the outside button when the vehicle is locked. The other consideration is I would like whatever method I use to only consume power when changing states from active to not active but not consume power when idle in either state. IE: I can leave the car locked or unlocked in the garage and the system is not slowly draining the battery.

I have done this with a 2 wire door lock solenoid connected to an unused rear door connection on the central locking module. I have a frame to hold the solenoid and a micro switch so the solenoid presses on the microswitch or release so I can open and close the tailgate open button circuit. It works but feels a bit unnecessary when surely there must be an electronic way to do the same.

I purchased and was hoping to be able to use this latching relay from Ali and connect the set and reset pins to the brown and white lock and unlock wires of the central locking module. The latching relay load would be the tailgate button circuit which the latching relay would create an open circuit when the car is locked and close the circuit when the car is unlocked so the button would work when unlocked but not work when locked. I have tested this and it works but because the brown or white wire holds the connection to ground, about 65mA continues to flow through the coil after the latching relay switches. I would prefer no power consumption and I don't think the relay is designed to have constant power through the coil. Only a ground pulse to each coil to change the state.

The brown and white wires from the central locking module appear to be a ground source for their state IE Brown is ground when locked and White is ground when unlocked but I'm not certain of that because if I ground each wire separately to central locking system locks and unlocks.

So, I guess I am looking for a circuit or 2 individual circuits that uses the ground on brown or white to then pulse a ground to the set pin (or reset pin) on the latching relay but not use any power while idle.

I was looking at this post where the user is looking for a ground pulse but the situation looks to be a bit different.

Or maybe I am looking at it all wrong and there is a simpler solution?

Does anyone have suggestion how I can work with what I have to disable the outside tailgate opening button when the vehicle is locked?

Hope all of that makes sense, I enjoy little electrical/electronic projects but am not always sure of correct language to use when describing things.

Thanks.

Hi,

Do you mean you are looking for an automatic system where all you have to do is lock the doors as you normally would, and have that disable the outside switch?
Why do you need a switch outside though, why not have it inside the car.

 

Hi,

Do you mean you are looking for an automatic system where all you have to do is lock the doors as you normally would, and have that disable the outside switch?
Why do you need a switch outside though, why not have it inside the car.

Yes. The outside switch is so I can open the tailgate while standing at it. There will be an inside button too and boot release on the alarm remote. The solenoid and switch/s are taking place of all handles , levers and linkages. The old setup had a finger loop with a key. The key pressed in when unlocked and mechanically release the catch. I’m replacing the key with a Mazda button so there is still the old design but newer tech. It still has the finger loop to hold while pressing the button allowing you to pull the tailgate open once the solenoid releases the catch. I’m modernising the old design.

I’ll try to draw up the circuit and post an image.

 

Yes. The outside switch is so I can open the tailgate while standing at it. There will be an inside button too and boot release on the alarm remote. The solenoid and switch/s are taking place of all handles , levers and linkages. The old setup had a finger loop with a key. The key pressed in when unlocked and mechanically release the catch. I’m replacing the key with a Mazda button so there is still the old design but newer tech. It still has the finger loop to hold while pressing the button allowing you to pull the tailgate open once the solenoid releases the catch. I’m modernising the old design.

I’ll try to draw up the circuit and post an image.

Ok great.

It might be hard to detect when the doors were locked though unless you had access to whatever controlled the door locks. You might have to have the schematic for your car electrical system.

Not sure what you mean by a 'finger loop and key". A key switch would certainly work, but you'd have to carry a separate key on your keychain for that.

 

I would use the Interior-Dome-Light-Circuit to provide a Ground for the Exterior-Push-Button.

This would require having any Door at least slightly ajar for the Exterior-Push-Button to work,
but You could supply a second independent-separate-Ground through the Alarm-System,
so the Key-Fob-Remote would still work in any case.

But personally ...........
I wouldn't even consider drilling a hole in the Car-Body just to have an Exterior-Switch.

Stop complicating things.
This is easy.
.
.
.

 

I have tested this and it works but because the brown or white wire holds the connection to ground, about 65mA continues to flow through the coil after the latching relay switches. I would prefer no power consumption and I don't think the relay is designed to have constant power through the coil. Only a ground pulse to each coil to change the state.

A 4700μF capacitor at each of the relay control inputs should give the desired short pulse to set/reset the relay with a very small quiescent current (below):
The capacitor generates a pulse of current to the relay coil with a decay time to 1/2 the maximum current in about 0.5s (red trace) below when the lock input signal goes low (green trace) which should be sufficient to toggle the relay.
If not you could try a larger capacitor.

R1 generates a small (120µA) of current when the input signal is low, which will is likely below the self-discharge rate of the car battery.

 

You might have to have the schematic for your car electrical system.

Not sure what you mean by a 'finger loop and key".

The car is from the late 70’s and the door locks are manual key or internal laver. I am adding central locking with door solenoids to the 2 front doors. The solenoid control module has 2 separate wires marked lock and unlock for the alarm system to control the locking and unlocking. It appears each wire becomes a ground in its lock or unlock status. The alarm would ground the lock or unlock wire to control the locking and unlocking.

‘Finger loop and key’. It’s hard to describe but it’s just the original setup for unlocking the tailgate and opening it from the outside. In better words, it’s the key barrel lock and handle combined into one unit.

the key barrel lock is broken and I cannot get parts easily. I’m removing the key barrel and replacing with a momentary button switch to activate the open solenoid via a relay.
I’ll put better photos and schematic shortly.
Thanks.

 

This would require having any Door at least slightly ajar for t
but You could supply a second independent-separate-Ground through the Alarm-System,
so the Key-Fob-Remote would still work in any case.

I’d prefer it to operate the same as some new cars. They have a press button on the outside, one one the dashboard and another via the remote key fob.

At the moment it all works except that the external press button remains active when the car is locked.
The setup for the switches and alarm to operate the solenoid is similar to dome lights where multiple switch’s grounding the circuit. I’m mine the external switch, internal switch and alarm system provides separate paths to ground for the relay coil that drives the solenoid. I’ll post photos and schematic shortly.

But personally ...........
I wouldn't even consider drilling a hole in the Car-Body just to have an Exterior-Switch.

Stop complicating things.
This is easy.

I’m not drilling new holes, I’m replacing the key barrel lock with a press button. Hard to describe the original setup but the key and handle are combined into a small piece used to open the tailgate from outside. Hopefully it’s not too complicated, it already works except the external press button remains active when locked.

 

A 4700μF capacitor at each of the relay control inputs should give the desired short pulse to set/reset the relay with a very small quiescent current (below):
The capacitor generates a pulse of current to the relay coil with a decay time to 1/2 the maximum current in about 0.5s (red trace) below when the lock input signal goes low (green trace) which should be sufficient to toggle the relay.
If not you could try a larger capacitor.

R1 generates a small (120µA) of current when the input signal is low, which will is likely below the self-discharge rate of the car battery.

View attachment 325721

This is the sort of thing I imagined, l’ll just need to get my head around how it fits within my circuit and then where to install it on the wiring loom in the car.
I’ll post some photos and a schematic shortly
Thanks.

 

Both my 2007 and 2017 have that hidden button easily accessed outside, and when the car is unlocked the butto allows a release and the liftgate opens. and when the car is locked the button does nothing. So on your wonderful remote module is there a wire available that changes state between locked and unlocked???
So all you really require is a simple latching relay driven along with the door lock/unlock solenoids. And when the doors get unlocked, then a contact on the latching relay is closed and +12 volts is supplied to the liftgate unlatch solenoid so that when the button is pressed the other side of the solenoid is grounded, and it operates and the rear opens. One single latch/unlatch relay.
But I think you said that the lock/unlock is constantly on in which case I would return the whole mess for a refund.

 

But I think you said that the lock/unlock is constantly on in which case I would return the whole mess for a refund.

That’s about it in a nutshell. I thought the latching relay would work and it does but because of the constant ground I have about 65mA after switching states and also the security issue of the press button working while locked.
Thanks.

 

OK, the cheating fix is to add series capacitors, so that once the capacitor charges current drops to zero, plus capacitor leakage. Two series capacitors with attention to polarity, and possibly just 100 MFD at 24 volts or better.

 

Thanks everyone, appreciate your input. Here is the wiring diagram of what I have setup and the idea how to de-activate the exterior press button when the vehicle is locked. It is working but due to the constant ground for each state at the central locking module there is 65mA flowing through the latching relay coil at all times. It's not designed for permanent power at the coil and the vehicle is not driven daily so I'm being mindful of the battery being drained whist parked in the garage for weeks.
I will head to the electronics shop and grab a few bits to test crutschow and MisterBill2's suggestions. Hopefully I don't let too much smoke out.

Another question, Should I include diodes/resisters or other components any where in the circuit so there isn't any backflow (sorry do know the proper term) of power or ground into any of these modules?

 

Additional to above diagram. The central locking module is also powered and grounded. I forgot to draw it. The central locking module is controlled by providing ground to either the lock or unlock wire. The wire then remains ground unitl the other wire is grounded.

 

Why not just add a micro switch to one (Or both ) door locks so that when the car is locked the contacts on the micro switch are open. Connect these contacts in series with the boot push button.
You may be able to use a reed switch and magnet in place of the micro switch depending on the design of the door lock actuators.

Les.

 

Why not just add a micro switch to one

I had considered using a micro switch inside the a door but wiring space in the rubber grommet that goes between the body and door is already full.

I did make a small frame to hold a door lock solenoid and micro switch. The solenoid was connected to the unused rear door terminals of the central locking module and pressed or released the micro switch. It worked well and I could mount it anywhere on the car but it felt a bit unnecessary. I might end up using that method again if I can't get the electronic version working.

Thanks.

 

After reading through the thread again I think that you you are saying that the lock and unlock wires stay at ground rather than pulse to ground. (For this to be the case the lock actuators must be motors with limit switches rather than solenoids so that they take no current when they reach the locked or unlocked position.) If my understanding is correct then connecting the outside push button to the unlock wire instead of directly to ground should work.

Les.

 

To make the latching relay not consume power constantly, just add an electrolytic cap in series with the +12 VOLT FEED. Current will only flow until the cap is charged. Leakage will discharge the cap after a while. Or add a 1 MEG shunt resistor.
Also, if those loc/unlock devices use 5 wires, they are much more than simple solenoids.

And one big concern is how do you get in when the battery is dead?? That is the fatal issue with not having a non-electric unlock means available.

 

Thanks everyone, appreciate your input. Here is the wiring diagram of what I have setup and the idea how to de-activate the exterior press button when the vehicle is locked. It is working but due to the constant ground for each state at the central locking module there is 65mA flowing through the latching relay coil at all times. It's not designed for permanent power at the coil and the vehicle is not driven daily so I'm being mindful of the battery being drained whist parked in the garage for weeks.
I will head to the electronics shop and grab a few bits to test crutschow and MisterBill2's suggestions. Hopefully I don't let too much smoke out.

Another question, Should I include diodes/resisters or other components any where in the circuit so there isn't any backflow (sorry do know the proper term) of power or ground into any of these modules?
View attachment 325769

So the capacitors would go in series with the Lock and Unlock connections to the Latching Relay (positive polarity to the relay coil).

I would also add a diode (e.g. 1N400x) from the Tailgate opening solenoid coil to ground (cathode to ground) to protect the relay contacts from any inductive spikes.

 

Hi crutschow, I agree with your suggestion of connecting a diode i parallel with the tailgate unlock solenoid BUT I do not agree with the suggested polarity of that diode. It should be the anode end to ground.

Les.