relay, fog lights, headlights

Printed From: the12volt.com
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=126414
Printed Date: May 13, 2024 at 6:38 PM

Topic: relay, fog lights, headlights

Posted By: garypaquette
Subject: relay, fog lights, headlights
Date Posted: March 03, 2011 at 3:44 PM

Hi,

I have hooked up my RV fog light as DRL, using a regualr relay that when the ignition is on the fog lights are on too.

But I want to disable the fog lights when the normal headlights are on. So a relay the will interrupt versus create a connection when the power is applied to the relay.

What should I be looking for?

Gary

Replies:

Posted By: oldspark
Date Posted: March 03, 2011 at 6:03 PM

Instead of grounding the relay's coil, connect it to the headlight +12V switched supply.
Provided the (headlight) resistance is low enough, the relay will energise thru the lights when off.

No problem with old lamps. (HIDs might be different...)

Posted By: Ween
Date Posted: March 03, 2011 at 6:09 PM

hi,
you'll need a SPST normally closed relay, or SPDT relay...a bosch type relay will be fine.
wire as follows:
terminal 86 to headlight switch, headlight output...has power when headlights are on.
terminal 85 to ground.
terminal 30 and terminal 87a will be used interrupt the ignition feed or ground of your DRL/fog light relay. you can remove the ground from the DRL relay and connect to terminal 30, then connect a wire to connect terminal 87a to the ground side of the DRL relay....terminals 30 and 87a are interchangeable in this application.
mark

Posted By: garypaquette
Date Posted: March 03, 2011 at 6:27 PM

Very cool - I will give that a try.
Any thoughts or ideas on where to get the relay. I am in San Diego and most people give me the confused look when I ask about relays :-)

Posted By: Ween
Date Posted: March 03, 2011 at 6:37 PM

relay...car audio shop, best buy, radio shack, auto parts store, fry's?

Posted By: oldspark
Date Posted: March 03, 2011 at 11:13 PM

But you already have the relay....
!?!

Posted By: garypaquette
Date Posted: March 03, 2011 at 11:18 PM

@oldspark
Yes - I will try your suggestion first as the headlights are HID's The other suggestion will be my next step.