# How to interrupt low beam with a relay?

prince504
Copper - Posts: 108
Joined: December 25, 2015
Location: United States
Posted: June 08, 2016 at 10:26 AM / IP Logged
A friend of mine has a Silverado 2002 and he says his low beams automatically come on at night & can't be shut off. He blacked out his truck & wants to be able to go into "stealth" mode for looks but can't shut of the lights.
Could I use a relay & switch to interrupt the auto headlights wire that runs to the low-beams at the switch by the steering wheel column?
i am an idiot
Platinum - Posts: 13,598
Joined: September 21, 2006
Location: Louisiana, United States
Posted: June 08, 2016 at 10:26 PM / IP Logged
Any time you put 12 volts across terminals 85 and 86 of a relay it will open the circuit from terminals 30 and 87A. If you cut the wire going to the low beams and connect the 2 ends one to 30 and the other to 87A, then use the switch to energize the coil (terminals 85 and 86) the low beams will turn off.
prince504
Copper - Posts: 108
Joined: December 25, 2015
Location: United States
Posted: June 08, 2016 at 10:42 PM / IP Logged
That's the idea I had too but was worried it might hurt sth. Thanks for your input!
On a different topic, if you used a relay to power a pair of fog lights for a vehicle that used 55W bulbs, what size fuse would you recommend using?
Using Ohms law, would it be --> (55 + 55)W / 12V = 9.17A...
Therefore, would you fuse them at 10A?
Thanks
KPierson
Platinum - Posts: 3,527
Joined: April 14, 2005
Location: Ohio, United States
Posted: June 11, 2016 at 9:30 PM / IP Logged
prince504 wrote:
 On a different topic, if you used a relay to power a pair of fog lights for a vehicle that used 55W bulbs, what size fuse would you recommend using? Using Ohms law, would it be --> (55 + 55)W / 12V = 9.17A... Therefore, would you fuse them at 10A? Thanks
Your nominal load should not be more than 75% of the fuses rating. So, a 15A fuse shouldn't have a nominal load above 11.25A. I would therefore use a 15A fuse in this application.
Kevin Pierson
prince504
Copper - Posts: 108
Joined: December 25, 2015
Location: United States
Posted: June 13, 2016 at 4:50 PM / IP Logged
Very good info. Thanks!

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