Momentary Switch to Operate Central Locking Lock/Unlock

Printed From: the12volt.com
Forum Name: Car Security and Convenience
Forum Discription: Car Alarms, Keyless Entries, Remote Starters, Immobilizer Bypasses, Sensors, Door Locks, Window Modules, Heated Mirrors, Heated Seats, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=145135
Printed Date: May 17, 2025 at 6:36 PM

Topic: Momentary Switch to Operate Central Locking Lock/Unlock

Posted By: old_tvr
Subject: Momentary Switch to Operate Central Locking Lock/Unlock
Date Posted: January 03, 2019 at 7:35 AM

Hello. I'm looking to use a momentary switch in my classic car to operate the door lock/unlock solenoids as a central locking feature. The solenoids require a +12V pulse to operate on either the lock or unlock inputs.

So, I'm trying to find a circuit such that:
First presss - doors locks (and a LED lights)
Second press - doors unlocks

The circuit then cycles on further presses.

Additionally, the momentary switch I would like to use has a LED that lights on closure so that would be nice to use that on the lock signal.

I was hoping to use the following posted circuit:

https://www.the12volt.com/relays/relaydiagram65.html
posted_image

but I'm not sure what the latching relay type is. Is it an impulse latching relay? Could someone please suggest a part number that is commonly available?

Also, I'm not quite sure how this circuit works as I don't understand how the latching relay in this circuit is reset for additional presses of the switch. Could anyone shed some light on this?

Replies:

Posted By: geepherder
Date Posted: January 03, 2019 at 7:58 AM

You probably can't pick this up at your local electronics store, but easy to order online:

https://www.altecautomotive.co.uk/latching-relay-12v--25a--braltry0-728-02-23-3640-p.asp

It's also important to note this relay requires a negative pulse to switch, not a positive. That means the diagram will need to be modified.

Also, even though the terminal configuration looks like a typical automotive relay, it says they will not fit a standard relay socket. You'll have to use individual connectors for each terminal.

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My ex once told me I have a perfect face for radio.

Posted By: old_tvr
Date Posted: January 05, 2019 at 3:39 AM

Thanks. Do you think the following cheaper relay from RS components (UK) would be a suitable alternative to the Durite?

Part no 718-1878.

It looks like a non polarised impulse latching relay that doesn’t specifically require the momentary switching on the negative side. I’m not worried about it not having the standard spade connectors.

I couldn’t find any other cheaper non polarised impulse relays that are easily bought in the UK.

Posted By: geepherder
Date Posted: January 05, 2019 at 7:11 AM

That looks like a great option. There's only one way to find out for sure.

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My ex once told me I have a perfect face for radio.