how do I wire this relay? | Ford Explorer Forums - Serious Explorations

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how do I wire this relay?

October 21, 2003
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I have a Bosch 20/30 amp 12volt relay here that I want to wire my driving lights to but I have no idea how to wire a relay. it is a 5 pin relay with numbers 85 , 30 , 86,87a,and 87 on the terminals, i have a wire harness for the relay it has a yellow, red, blue and white wire coming from it and a black wire as well. Imassuming the black wire ia a ground. well its maybe not a ground becuase i took the tape off the harness and the black wire is connected to the yellow wire on the relay and it was connected to a constant 12 volt source on my truck when i removed it
thanks for the info , mike

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You will not use all 5 pins. Pins 85 and 86 will be the positive and negative to your coil. Pin 85 will receive power from your switch and 86 will go to ground. Pin 30(bigger amps means bigger wire) will be the main power for the driving lights from the battery( fused 0f course) and pin 87 will be the ground. Wired this way your driving lights will not be on unless you turn on the switch. You can either tap off the existing headlight switch in which case your driving lights will always be on when running headlights or use a seperate switch for the driving lamps. In some states it is illegal to run driving lamps without running head lamps. If that is the case you may want to run from the headlamp switch thru another switch(allowing you to turn on or off the driving lamps) and then just run the main power thru the relay to the driving lamps.

Did I confuse you yet??:D

Found this pic...hope it helps


im sorry i forgot to add this is for an after market foglight setup i have a switch panel my my lights will be switched from. but thanks for the info its very helpful !


so pins 86 and 87 will both be grounded? and so pin 85 will be what the power wire from the lights will be run to?

Pin number 85 is the hot wire from your switch, #86 would be the ground. #30 would be the main hot wire from the battery and #87 would feed the lights. The lights may have 2 wires in which case the other goes to ground(or back to the battery). This will allow you to use your existing switch to turn the lights on/off without running full power(20/30 amps) thru the switch. The full power will just run from the battery thru the relay to the lights. Hope this helps

ok one more question the wires running from the switch, one goes to pin number85 now where does the other switch wire go to?

from battery or "hot" (fused) to switch then one wire from switch to #85 then #86 to ground then from battery(larger gauge for higher amps) to #30 then #87 to hot side of lamps then second wire form lights to ground(if no 2nd wire from lamps then the case of the lamp must be grounded to the frame/bumper where it is mounted

ok I think I understand everything now, thank you for all your help.


No problem..Glad to help:D