using relays to mimic and gate?
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Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=94103
Printed Date: July 01, 2025 at 5:59 AM
Topic: using relays to mimic and gate?
Posted By: mazda6fan
Subject: using relays to mimic and gate?
Date Posted: May 20, 2007 at 9:42 PM
I've got retrofitted HIDs installed in my car's low-beams. HID components are such that they should not be turned on and off in rapid succession. Once they've been turned on, they should be left on for at least a few minutes before turning them off.
I have discovered that if my low-beams are off and I flash my high-beams (to signal something to another driver) my low-beams will actually activate for the brief duration of the high-beam flash.
This rapid on-off action is very bad for my ballasts, so I've forced myself to stop the high-beam flashing... but I sometimes manage to forget.
I'm wondering:
Can I use a relay to prevent the low-beams from coming on, if say I provided +12V from another circuit that I know is live when the low-beams are "officially" switched on?
Here's what I'm thinking:
When the low-beams are off, so are my sidemarkers. It is in such a condition that I wish to prevent the low-beams from being activated when the high-beams are flashed.
When the low-beams are switched on, then my sidemarkers are also on. In this case, its ok to flash the high-beams since the ballasts won't get affected.
My question:
Is it possible to wire up a relay (or series of relays) in such a way that it will only turn on my low-beams if there's also power coming from the sidemarker?
In digital electronic terms, it would be like having an AND gate after the headlight relay with one input coming from the sidemarker. If the sidemarker is on and if the headlight relay is also providing power, then and only then turn the headlight on.
Is this possible using only relays?
TIA.
Replies:
Posted By: mazda6fan
Date Posted: May 20, 2007 at 9:47 PM
mazda6fan wrote:
Can I use a relay to prevent the low-beams from coming on, if say I provided +12V from another circuit that I know is live when the low-beams are "officially" switched on?
Apologies... the above statement should read:
Can I use a relay to prevent the low-beams from coming on, unless I provide +12V from another circuit that I know is live when the low-beams are "officially" switched on?
Posted By: dualsport
Date Posted: May 20, 2007 at 10:04 PM
Seems like all you need is a single relay with the coil energized from your side marker power, and just interrupt the control for your HIDs with the relay contacts.
That should do what you're looking for-
Posted By: mazda6fan
Date Posted: May 20, 2007 at 10:26 PM
Ahh yes, thought about that. Problem with that is that the sidemarkers come on at the parking light stage, which is one "click" before low-beams on the lighting control stalk.
I'd end up with low-beams on at the parking light stage.
Posted By: dualsport
Date Posted: May 21, 2007 at 8:31 AM
That's only if you connected power to the relay contacts; instead, you need to connect what normally goes to your HID low beams (from your usual switch). You need to just cut the wire that normally runs to the HIDs and use the relay term 30/87 to bridge it when appropriate. It only interrupts the connection to the HIDs when you have the parking lights off. If you only have the parking lights on, the HID will not be turned on.
Posted By: mazda6fan
Date Posted: May 21, 2007 at 11:30 AM
Aha... like putting two relays in series?
That'd work!
Thanks for the help.
Posted By: dualsport
Date Posted: May 21, 2007 at 7:19 PM
Sorta in series, but not really- If you already have an existing relay for the HIDs, I'd use the added relay to interrupt the coil power, rather than the HID power. Either way would work, but using it for the relay coil power instead saves a bit of voltage drop across the relay, and it's easier on the extra relay.
Posted By: hotwaterwizard
Date Posted: May 21, 2007 at 10:16 PM
------------- John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !
Posted By: hotwaterwizard
Date Posted: May 21, 2007 at 10:52 PM
Here I made an easy Diagram for you. 
------------- John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !
Posted By: dualsport
Date Posted: May 21, 2007 at 11:14 PM
This is what I meant by using the added relay to interrupt the coil current of the original relay-
Posted By: hotwaterwizard
Date Posted: May 22, 2007 at 7:47 AM
That would work but this is another way. 
------------- John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !
Posted By: mazda6fan
Date Posted: May 23, 2007 at 12:27 PM
Awesome diagrams everyone. Thanks for the help. Should have this issue taken care of in no time. :)
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