[cal1320]

I came across this site that has lots of useful info reguarding the wiring of relays. Thought I'd pass it along.
Relay Diagrams - Quick Reference

[timothale]

After a computer crash and the one in my shop stolen along with a lot of other stuff, I've started printing out info I want to save for reference and keeping it in notebooks.

[EOD Guy]

90% of all relays work off the same principal......

For example a bosch type relay.....
There is a coil with two terminals, (85 and 86) it doesn’t matter which terminal gets pos or neg.

If you hook up constant 12v to one terminal (85)....... the other terminal (86) connected to one side of a switch, the other side of the switch connected to a ground, when the switch is thrown it provides and ground (neg) and activates the coil.

If you hook up constant neg (ground) to one terminal (85)....... the other terminal (86) connected to one side of a switch, the other side of the switch connected to a 12v source, when the switch is thrown it provides and pos and activates the coil.

Depending on what you want .... either way works just as well. I like to hook fused, constant 12v to the coil (85 or 86) and use a switched neg to activate the relay. IMO that keeps the hot wire short and reduces the resistance etc.......

On most automotive bosch type relays that you can purchase at most auto parts stores, will also have a common terminal (30) and a normally open or NO terminal (87) and there are some that have a normally closed (NC) terminal (87a).

Depending on what you want to do would determine if you needed a 4 or 5 terminal relay.

For example........ You wanted to hook a air horn up on your vehicle and you wanted to use the steering wheel horn button to activate it, but you still wanted to use the normal car horn ...... that’s where a relay works perfectly. You would find the original wire that connects to your normal horn and disconnect it from the normal horm, make a new wire and connect it to the normal horn and run it to NC (87a) terminal.

Take the original wire and hook it to the common terminal (30), since 87a and 30 are making contact, when you press the steering wheel horn button the normal horn honks. Next you hook your air horn pwr lead to NO (87) terminal, now when the relay is energized, as outlined above, it disconnects terminal 87a NC from the common (30) and connects terminal 87 NO to the common (30) so now when you press the horn button pwr is routed to the air horn.

Basicly it’s an “either”/”or” type circuit

[EOD Guy]

Let me add to the above post......

If you are using a 5 terminal relay, instead of a 4 terminal, to switch something on for example..... fog lights....

I like to hook the hot lead to terminal 87 (NO) and the fog light feed to the common terminal (30). My reasoning.... When the relay is not energized, terminal 87a (NC) is dead.

If pwr were on terminal 30 and the light feed was on 87, then when the relay was not energized terminal 87a would be hot and increase the chances of a short circuit.

[EOD Guy]

One of the neatest things I've done with relays........

On my 67, I have after market pwr windows, my OEM window cranks are my switches, I didn't want those ugly door switches and I wanted the interior to look bone stock........

The issue: I couldn't roll down the pass window while i was driving etc......

Solution: A stainless steel micro push button switch and four relays. Press the micro switch and it switches the relays to allow the drivers window switch to control the pass window.

Works very well

[ween]

hi,
although i haven't seen lately, some older bosch relays do have a suppression diode across terminals 85 and 86. in that case terminal 86 is the positive and 85 is the negative. wire it backwards and you get a short circuit, blown fuse, smoke let out of the electronics module controlling the relay, etc...not a good thing. the nice thing is that bosch did put a little symbol for the diode on the case of the relay to show that there is one present. if you sourced relays from used vehicles, gm i know did have them back in the 90's, couldn't hurt to look.
mark

[JeffB]

For a good explanation of why you should use relays this spells it out in EZ to understand terms:Custom Cars Classic Hotrods Streetrods-Watsons StreetWorks

[EOD Guy]

Here's one for Door poppers using a neg pulse from a remote key fob or a hidden switch to activate.

[EOD Guy]

Door popper using Pos pulse

[EOD Guy]

Very basic cooling fan

[EOD Guy]

Pwr antenna using two relays

[EOD Guy]

Pwr door locks

[EOD Guy]

67 Camaro RS headlight doors

[DanielC]

This relay, available from Summit Racing has two 87 terminals.
Handy for wiring two headlights to one relay.


Because of the diode in some relays, keep pin 86 positive, and pin 85 negative. You can switch either coil feed wire, that does not matter.

The relay you use may not have a diode in it, but there is a possibility you may need to replace the relay at a later time, or the next owner of the car will. If you wire the coil of the relay with the wrong polarity, you have to make sure the relay you replace it with also does not have the diode.

The diode is used to suppress inductive kick back. Just like the primary side of the ignition coil, when a relay coil is switched off, the magnetic field collapses, and that induces a brief high voltage spike in the relay coil.

[crdnblu]

Check this out:

http://www.dlcparts.com/images/BoschGuide.pdf