Relays for Dummies

[WKderF]

Ok I am going to explain how relays work and tell you how to wire a few simple relays up.

Your standard relay that every uses or get with a fog light kit or at the auto shop looks like this. It has four sometimes five tabs. The fifth tab is generally in the center. Four tab models do not have the center tab. They are label like this

-- 87
85 I -- I 86
87A
I 30

The I and -- represent the tabs in this picture

Top is 87
left 86 center 87A right 85
bottom 30





I relay needs power ( +12V ) and ground( -12V ) on tabs 85 and 86. Doesn't matter which gets which generally. Lets say 86 gets +12 V and 85 gets -12 V. OK?

When the relay has connections and power on these to tabs it is "energized". It switches conections between the tabs. All it is is a electrical switch. So when 86 has +12 V and 85 has - 12V (ground) it is energized and it switches connections between the tabs. When it is "energized" or "switched on" the tabs 30 and 87 are connected to each other internally.





When it is not "energized " or "switched off" the tabs 30 and 87A are connected. If you only have a 4 tab relay this does not apply.


So if +12V or -12V (ground) ins not present. This is how the tabs wiull be connected.





Lets do a simple relay. this works for horns or fog lights.





Let do starter kill , like most alarms.

This could work for the ignition wire too.. wink wink


Now this is a tricky one. See when the alarm is off the relay is not energized. So the connection is between 30 and 87A. So the starter wire is connected. But when the arlarm is on... it has - 12V at 85 and when the starter is turned it get +12V at 30 and moreimportantly 86, which energizes the relay and makes the relay change the connections from 30 and 87A to 30 and 87. Which dissconnects the starter.




Ok now we switch between horns. This will require a switch.

The switch will be connect to the relay and to ground. The horn wire under the hood are +12V. If you wnat you can use another relay to up the power then connect the output of that relay to the 30 tab of this relay. When the switch is oof the stock horn blows. When it is on the hellas blow.






The reason I jumper the horns +12V or the starter wires +12 V is for ease of use and one major thing. If you used a +12V constant. the rlay coulkd be on for long periods of time. Causeing it to heat up and if parked for a week it could drain a battery dead. So I always think how long and how much will this relay be energized.

One last security one. this will not work for everyone bit it cna be tailored if you think about it. It will work for DEI alarms on Subys.
the colors are standard DEI colors. You may need to diode your starte kill wire at the starter kill and at the relay so that they dont feed back and forth to each other. The silver band on the diode should face away from the relays when you wire it in.

What this will do is give you a pulsing horn honk with your flashing parking lights when you door is opened. I sort of 2nd alert. A cheap way to get that responder type alarm. So you can physically hear if they've gotten inside your ride or if its a frigging cat.

When the siren is going off, the door is opened and the parking lights are flashing while the alarm is armed, the horn will honk.

[MuddyREX]

Awesome post Fred.

[Jeffros Spec V]

WOW, I'll just take it to Fred.

[SoStock92]

Just so everyone knows - Bosch 30A automotive relays can be triggered with anything around 7 volts as well.

[WKderF]

pic links updated for reference.

[camopaint0707]

great information, question though, how would I be able to have a set of aftermarket lights come ON when the car is turned OFF. Then have the lights go OFF when the car goes ON

[camopaint0707]

bump for my previous question

[camopaint0707]

no one has an answer for me i suppose

[champ_6]

wire parking lights to 86 and wire your alternative lights to 87a... are you looking to kill your battery?

[assault187]

Originally Posted by camopaint0707

great information, question though, how would I be able to have a set of aftermarket lights come ON when the car is turned OFF. Then have the lights go OFF when the car goes ON

87 will be unused
87a to 12v constant
30 to lights
86 to ground
85 to Ignition


Pins 87a and 30 always have continuity when the relay is at rest, when the relay is powered those two pins lose continuity. If you want the lights to power down with the car running, simply use ignition power for the relay.

[camopaint0707]

i don't get how that would kill my battery, thank you assault.
My next question (which I made another thread for as well) but if I have some aftermarket sidemarkers, they have only two wires coming out the back, a positive and negative. How do I wire them up so that they are on when my taillights are on, but also blink whenever I put on my turn signals? Thanks.

[assault187]

Originally Posted by camopaint0707

i don't get how that would kill my battery, thank you assault.
My next question (which I made another thread for as well) but if I have some aftermarket sidemarkers, they have only two wires coming out the back, a positive and negative. How do I wire them up so that they are on when my taillights are on, but also blink whenever I put on my turn signals? Thanks.

This is a little more complicated being its only a 2 wire, single filament bulb. Its late so my thinking is limited but I do have a way to do this off the top of my head.


Pin 87: Unused
Pin 87a: Parking light wire (from vehicle)
Pin 30: 12v power wire on side marker light
Pin 85: Chasis ground
Pin 86: Turn signal wire (from vehicle)

If set up in this order, Your marker lights will be lit when the parking lights are on and when the relay sees the 12v signal from the turn signal, it will temporarily break continuity causing the marker light to flash like a turn signal.

Note: Turn signal flash may not flash in sequence with the factory signals on the car.

[camopaint0707]

thank you so much assault, i'll attempt it tomorrow and let you know how it goes, thank you

[camopaint0707]

Originally Posted by assault187

This is a little more complicated being its only a 2 wire, single filament bulb. Its late so my thinking is limited but I do have a way to do this off the top of my head.


Pin 87: Unused
Pin 87a: Parking light wire (from vehicle)
Pin 30: 12v power wire on side marker light
Pin 85: Chasis ground
Pin 86: Turn signal wire (from vehicle)

If set up in this order, Your marker lights will be lit when the parking lights are on and when the relay sees the 12v signal from the turn signal, it will temporarily break continuity causing the marker light to flash like a turn signal.

Note: Turn signal flash may not flash in sequence with the factory signals on the car.

ok so I tried this out today. When the taillights are on, the light is on, when the taillights are on and the turn signal is on, it flashes opposite the turn signals. Which is good, that is what i want. But when the taillights are off, the light does not flash when I put on the turn signals. The relay still makes a click sound however.

[assault187]

were gonna need another relay for each side for this then. When I wrote that explanation, I didn't take into account the side markers usage with the parking lights off.... Like I stated, it was late shoot me a PM tmrw to remind me to come back into this thread and post a new explanation. I would do it now but its 5 am and I haven't slept yet...and you saw what happened last time lol. We'll get you squared away with this.

[camopaint0707]

PM sent, thank you.

[assault187]

I played around with different configurations for a while so see what would work. I haven't come up with anything that will power the turn signal with the parking lights off, illuminate with parking lights and also flash while the parking lights are on. It seems we may need a dual filament bulb setup for this application.

Sorry bud, I tried..

[camopaint0707]

what about using two relays? could it be done that way?

[assault187]

Thats what I was trying to accomplish but every configuration I come up with wouldn't work correctly

[camopaint0707]

damn this sucks, i wonder if creative cartunes could help