Powering a device via relay w/ 5V hood switch

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URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=7463
Printed Date: August 18, 2025 at 11:50 PM

Topic: Powering a device via relay w/ 5V hood switch

Posted By: 1max2nv
Subject: Powering a device via relay w/ 5V hood switch
Date Posted: January 01, 2003 at 12:51 AM

Here are some background information of what I'm trying to accomplish.

I want to turn on neon lights and strobe lights when the hood is open. They basically need switched +12V power. My car is a 1999 Nissan Maxima with factory hood pin switch. I believe it's a negative trigger hood pin switch. From reading the factory service manual, there are two wires at the switch. First wire is yellow with black stripe coming from the car's body control unit. The second wire is black (ground). The factory service manual states.

When hood pin switch is CLOSED(OFF), the yellow with black stripe wire is 5 volt.

When hood pin switch is OPEN(ON), the yellow with black stripe wire is 0 volt.

Does this mean the hood pin switch is negative triggered?

Now, how do I use a relay to get switch +12V when the hood pin switch is in the OPEN(ON) mode? Please note the voltage is 5V.

Replies:

Posted By: brianh
Date Posted: January 01, 2003 at 8:02 AM

If the wire does what you say it does it should be a (-) trigger. Get you a relay and tie Pin86 to the Yellow/black wire. Come off your batterey with a 12 volt constant wire and fuse it for the total load of your lights. Run this wire to pin 85 and the to pin 87. Finally run a wire frompin 30 to your positive input for your lights. Good luck. Brian

Posted By: 1max2nv
Date Posted: January 01, 2003 at 10:31 AM

Thanks Brian...one last question for you. Would the +12V cause any problem to the +5V output of the car's body control unit? Like fried the unit?

Posted By: brianh
Date Posted: January 01, 2003 at 5:02 PM

No, the 12 volts is just there to turn on the coil. Think of the coil as a light bulb. You need both the hot wire and a ground for it to work. The 12 volts on pin 87 will be transfered to your lights to turn them on. It should work fine. Good luck Brian

Posted By: 1max2nv
Date Posted: January 01, 2003 at 7:36 PM

I'm going to use two relays so I can isolate the two circuits. Running a 12V wire to a 5V wire scares me posted_image

. The 5V yellow/black wire is coming from the ECU so maybe I should not use it as a ground.

Posted By: brianh
Date Posted: January 01, 2003 at 7:50 PM

Thats probably a good idea. Good luck with it. Brian