junk yard relays

[Uncle Skip]

Relays are really cool for our old trucks because you can use a really small wire to "trigger" a relay that can run up to 40 amps for any component you need that requires a lot of amperage, including the new halogen head lights, radiator fans, fuel pumps, A/C systems, etc.
As far as I can tell, there are two kinds..... 4 wire and 5 wire relays. While they do come in different load ratings, I only take the 30-40 amp relays.
Like I said, junk yards are a really cheap source of good relays in all kinds of sizes and configurations, but how to wire them?
Apparently there is an SAE wiring standard for 12 volt relays.
Who knew?
So, when you take one out of the junk yard, be sure to take as much wire as you can with the plug so you have something to splice into..... (don't cut it short).
Then, pull the plug from the relay and locate where each color wire goes into the relay and write it down. There are numbers inside the relay where the male prongs are and they hook up as follows.
30 - This is the 12 volt power to the relay and it is always hot. Direct from the fuse block or the battery.
85 - this is the wire that goes to what ever switch you used to use for your component. When you turn on your switch, it activates the relay and transfers the power to your component.
86 - This is your relay ground wire. Most always is black. If you don't ground it, the relay won't work.
87- this wire goes directly to what ever component you're going to power up. No power will go to it until the relay is activated by the switch on 85.
87-a (or b) - this is a terminal that isn't normally used. the wire going to this will be hot when the relay is off. I still haven't figured this one out, but I'll edit this post if I ever do. I just dead head this one and bury the it in the wire harness where no one can see it hanging there.
Relays are a wonderful thing.
*and one more hint. When you're locating your relays, put in a couple of dummys for systems you might add later. I don't have A/C yet, but I'm adding a relay for that, just in case.

[62galxe]

Skip thats some good info. Im trying to simplify this a little more. Hope it doesnt offend anyone. Relays are pretty simple. You have 2 connections for the coil. Think electromagnet. On a 12 VDC circuit one side is a switched 12 VDC and the other is ground. You have 3 contacts in the relay. 1 is moveable on a arm and the other 2 are stationary. This is where normally open and closed comes into play. You have power going to the moveable contact. When you have no power to the coil the normally closed contact has power. When you apply power to the coil the normally open contact has power and the normally closed turns off. You can get relays with multiple poles / number of contacts. The coil will control multiple sets of contacts. They make relays with off and on delay timers. Think time delay on your headlights when you turn them off. Heres a site with some good diagrams. http://www.bcae1.com/relays.htm

[HiBoy63]

Skip and 62galxe thanks for that tutorial I put it in my favorites to refer to when I get to that point.

[charliemccraney]

I was at the junk yard a couple weeks ago and noticed that some relay boxes are kinda modular. That is you can swap the sockets around within the box and there are different sockets - I noticed some that were not the common 4 or 5 prong relay sockets. Some of them were even very straight forward as far as mounting and lend themselves to customizing older stuff really well. I'll bet you can buy the terminals so that you can make your own bran new harness and not have to splice into the same wires.

[Truckrat]

Skip, thanks for posting that. It makes hooking them up a lot easier.
My 57 could use of few relays in it's wire harness for sure. There are none in it.
I think I need one for the horn. The pushbuttons don't seem to last very long. TR

[Fanatic]

I thought the same thing Skip...but now after dissecting that posted website..... it seems that the 87a terminal is hot when the relay is not energized and will turn off when it is energized. Not exactly sure what use this might have, but I'm sure someone here will come up with one.

Tim

[bcook07]

Here is an example where 87a is used.

The two relays are used together and you can get ground for the door lock actuators at all times. depending on which relay is active the opposite supplies the ground for the actuator.

[kstones63]

I thought the same thing Skip...but now after dissecting that posted website..... it seems that the 87a terminal is hot when the relay is not energized and will turn off when it is energized. Not exactly sure what use this might have, but I'm sure someone here will come up with one.

Tim

I used a relay for the torque convertor lockup and the third brake light.
86 - ground

85 - hooks to the brake light switch wire before the steering column

30 - key switched 12v instead of constant 12v

87A - goes to the torque convertor

87 - goes to the third brake light.

This puts switched power into the T.C. so it will lockup when it needs to.
When the brake lights come on, it transfers power away from the T.C. (87A) so it will unlock and puts power to the third brake light (87).

Kevin

[PFM-64f100]

To add more to this thread. This is the diagram to wire two power window switches to one motor.

[Uncle Skip]

These three junk yard relays switch my upgraded high and low beam quartz headlights and my electric fuel pump. There are fuses in the wiring just in case.

[unibody madness]

I have a problem with the 460s carb running dry after sitting for a while.
My carb man suggested running an electric fuel pump in line from the tank as a primer pump.
Switched power to relay from starter curcuit
ground to oil pressure sending unit (think idiot light)
pump power to the normally closed relay terminals.

Power is temporarily supplied to in line pump until oil presure comes up, when the engine fires
power is cut to primer pump
releasing switch to run position kills power to pump as well
John

[bmcgc]

Thats a good tip. Grab some fuses and light bulbs too. A 2 pack of light bulbs is running almost $5 and a box of fuses about $4 in the auto parts stores.

Salvage yards will give them to you or only charge a buck for a handful.

[foodstick]

I bought the relay with loom from LMC, it has the sockets for each headlight installed with a ground wire. then you run two red wires from the relay to the battery. It has a 3 wire plug that is supposed to go to your factory harness.. a red, a blue, and a black.. It gives no info on the wiring at that point. Is it as simple as ground the black and hook the other two wires to the low beam and high beam on the original two wire plug?

Love to get this hooked up without MELTING anything..

[Kid]

you guys amaze and confuse me all at the same time. I understand what you guys are talking about and how and why but when it comes to actually doing it I am dumbfounded

[foodstick]

It is done and DANG is it brighter than before.. holy !!!!