Taxi rooftop light

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=139023
Printed Date: December 01, 2021 at 4:09 AM

Topic: Taxi rooftop light

Posted By: jimd2p
Subject: Taxi rooftop light
Date Posted: May 27, 2015 at 7:39 PM

I am looking for some help in configuring a relay(s) for a taxi cab. I'm an auto mechanic and this is a bit out of my league.

My customer is wanting to be able to sit with the vehicle either running or key on and the rooftop light be on when vacant. Then when he hires a fare, the light goes off.

The trigger wire from the meter is 0 volts when vacant and 12 volts when hired.

Any help would be greatly appreciated.

Replies:

Posted By: davep.
Date Posted: May 27, 2015 at 8:17 PM
Use a SPDT relay. Standard 5-terminal cube tyco or bosch type.

30 = Hot in IGN or ACCY.(Or to a Retained Accy Power lead like the radio or power windows. The roof light will stay powered until a door is opened, or the RAP times-out. Would be a cool wrinkle).
87a = To roof light.
85 = Ground
86 = From taxi meter, +12V when hired.
87 = Not connected, insulate.

When key is ON (ACCY or IGN), 12V is available at terminal 30, and conducted through the Normally Closed contact 87a to the roof light. When meter is HIRED, the relay is energized, the contacts open, and the roof light goes out. Turn off key, roof light also goes out.

Posted By: jimd2p
Date Posted: May 27, 2015 at 8:27 PM
You're the best. Thank you so much. I'll get it done tomorrow

Posted By: hotwaterwizard
Date Posted: May 27, 2015 at 8:52 PM
A Relay will work great in this case. Is the Trigger Constant voltage output or Momentary output?
If it is Constant Voltage this Circuit will do the Trick.

If Momentary then it will be more Tricky.

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John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !

Posted By: jimd2p
Date Posted: May 27, 2015 at 9:34 PM
It's a constant as long as the fare is hired.

Posted By: hotwaterwizard
Date Posted: May 28, 2015 at 7:24 PM
Perfect! The Relay just reverses the polarity of the signal to do what you need,

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John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !

Posted By: jimd2p
Date Posted: May 28, 2015 at 9:13 PM
Put it in today and it worked great. Thank you so much for all the help. Customer is very happy.

Posted By: hotwaterwizard
Date Posted: May 29, 2015 at 9:33 PM
Thanks For telling the outcome.

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John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !