fogs on with parking lights and off w/ hb
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=125037
Printed Date: May 06, 2025 at 5:11 PM
Topic: fogs on with parking lights and off w/ hb
Posted By: jbh6e
Subject: fogs on with parking lights and off w/ hb
Date Posted: December 14, 2010 at 11:09 AM
Everyone I need to know how to wire a set of fog lights on with parking lights and off when high beam head lights are on. Its been along time since I've tried to wire dual 30 amp relays. I could use some help. Thanks
Bosch 30 amp relay
87
87A
86
85
30
Replies:
Posted By: jbh6e
Date Posted: December 14, 2010 at 11:38 AM
I'm installing these fog lights on a 92 - 95 civic. I'm make my own harness I just need to know how to wire the two relays.
Posted By: howie ll
Date Posted: December 14, 2010 at 5:52 PM
Legally (at least here) they should only come on with the low beams but any way here goes.
Relay 1.
Pos output from switch to 87a.
Pos from high beam to 86.
Ground to 85.
Output from 30.
Relay 2
Output from 30 on relay 1 to 86.
Ground to 85.
Battery via a 20 amp fuse to 87.
Lights out put from 30.
You switch should be fed from a source that goes to pos when the side (parking) lights are on.
Ideally I would use a third ignition controlled relay wired as such
Switch output to 86.
Ground to 85.
Ignition to 30 and out put from 87.
Wire this first in series with the original 1st. relay, this will prevent leaving the lights on with the ignition off.
Up to you.
Relays 1 and 2 need only be small 5 amp PCB types, half the price of regular relays as sold by DEI, R/Shack etc.
-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: howie ll
Date Posted: December 14, 2010 at 5:54 PM
Sorry I forgot!
Solder a 1N4004 diode between 85 and 86 one per relay with the bands towards 86.
-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: oldspark
Date Posted: December 14, 2010 at 6:18 PM
Two relays?
I was going to suggest wire the relay power as normal (fused +12V to 30 thru 87 to the (grounded) fog lights.
Then coil 86 (on) to the fog light controller (on/off +12V switch whatever) and the coil ground (85) to the hibeam (ie, +12V when on) or whatever you want to turn the fogs off when also +12V.
Plus a diode in the 85/86 line to prevent high beam on & "fog lights off" turning ON the fogs. (IE - Kathode - line end of diode towards 86 or away from 85.)
Plus a suppression diode if required between 85&86 ONLY if the above reverse-polarity blocking diode has been fitted.
Posted By: howie ll
Date Posted: December 14, 2010 at 6:22 PM
A much better idea Peter but I'd still add a second as an ignition (i.e.fail safe) interlock.
-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: oldspark
Date Posted: December 14, 2010 at 6:47 PM
Good point. I was assuming the fog switch/controller itself to be IGN controlled. (And I'd consider the reverse-blocking diode to endure off with hibeam-only essential.)
And on my 1965 vehicle I have a lights reminder ($1.30 plus 10-30 years LOL!) but I like lights independent of IGN. (Hence I can watch the girls thrashing to my stereo!)
|