Working out resistor values

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=572
Printed Date: August 20, 2025 at 4:54 PM

Topic: Working out resistor values

Posted By: naughtydog
Subject: Working out resistor values
Date Posted: May 02, 2002 at 4:45 PM

Can anybody explain how to work out the resistor value when working with "single wire central door locking". In the UK, the new VW polo for example has single wire negative pulse cdl and requires a resistor to unlock. How is the required value of resistor arrived at??
Is it a matter of trying various resistors until it works???

There must be some method and can it be done with a normal multimeter...

Regards

Naughtydog

Replies:

Posted By: the12volt
Date Posted: May 02, 2002 at 5:05 PM

Hi Naughtydog, yes, use your meter to measure resistance to ground during unlock on the lock/unlock lead to determine the value of the needed resistor .

the12volt

Posted By: naughtydog
Date Posted: May 03, 2002 at 1:32 AM

Ok,

I set my meter to the resitsance scale. I place the positive lead on my vehicle wire and the negative lead to ground. When I operate the locking, i should get a reading. Does that sound right

Naughtdog

Posted By: naughtydog
Date Posted: May 03, 2002 at 5:25 AM

Just a thought...Must this procedure be carried out with the vehicle battery disconnected to obtain the corrrect value required???

naughtydog

Posted By: Big Dog
Date Posted: May 03, 2002 at 7:13 AM

Just to add to the comments, this procedure explained before is correct:

Hi Naughtydog, yes, use your meter to measure resistance to ground during unlock on the lock/unlock lead to determine the value of the needed resistor .

the12volt

However, do your reading while turning the key in the drivers door cylinder.

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Prepare your future. It wasn't the lack of stones that killed the stone age.

Posted By: Big Dog
Date Posted: May 03, 2002 at 7:22 AM

Hey Naughtydog, is there a particular car that you're working on? Is it a Chrysler or a Mazda? This info can help us give you more exact info! posted_image

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Prepare your future. It wasn't the lack of stones that killed the stone age.

Posted By: naughtydog
Date Posted: May 03, 2002 at 9:03 AM

Thank fellas...i am just trying to grasp the concept a little better...no particular car!!

We did'nt clarify??? - do you test with the battery connected or not - or does it not matter either way...

Naughtydog

Posted By: wirewise
Date Posted: May 03, 2002 at 9:09 AM

Leave it connected.

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~wirewise~ Verify all wiring with your meter before making any connections!