A relay is an electromechanical device that allows a large electrical load to be
controlled by a separate, much smaller load.
A relay is composed of two separate electrical circuits. The rst circuit is
composed of a terminal that allows power in from a switch, an electromagnetic
coil, and a terminal to ground the coil. The second circuit is composed of a
terminal connected to battery power, a movable armature, a set of contacts, and
a terminal wired to your accessory.
When low current, controlled by a switch, ows through the coil side of the
relay, the coil is magnetized, the armature is pulled down, the contacts make a
connection, and high current is allowed to ow from the battery to the accesso-
ry.
Once the switch is turned o, current stops owing through the coil, a spring
returns the armature to its original position, and current is cut o to the
accessory.
Reduces load on OEM components.
Larger loads than normal can be controlled by the switch as the switch never
physically interacts with the larger load side of the relay.
Heavy duty switches are not needed since only a small amount of current is
required to energize the relay coil.
It is easier to use the correct gauge wire.
It is easier to control multiple accessories with a single switch.
One of the most common types of relays is the 5-pin Bosch style relay. This is
an example of the pin layout and function of a Bosch Style relay.
In this case, pins 85 and 86 are the low current coil circuit and pins 30 and 87 are
the high current accessory circuit. In this situation we will be ignoring 87a.
A typical Wiring setup would look like this:
Two relays will be needed.
Each relay will be connected to the same ACC power source, ground, and
positive post of battery.
But each relay (Pin 87) will need to be wired to a dierent red wire on the
switch box.
i.
ii.
iii.
If you want your switch box and accessories to function only when the car/ignition is
on, a relay will need to be placed between the battery and the switch box. You will be
using ACC/ignition power to trigger the relay which will then supply power from the
battery to the switch box.
Find an acceptable location to tap into ACC/ignition power (powered only when
the car/ignition is on).
Using a Bosch style relay, wire:
1.
2.
To correctly wire a Bosh style relay rst begin with steps one and two of the low
amperage wiring procedure.
Then wire the correctly colored wire from the switch box to pin 86 on the relay.
For example, if you want to control a light bar with switch A, you would connect
to brown wire to this terminal.
Connect pin 85 to ground.
Next, wire battery power to pin 30. It is a good idea to put a fuse in this wire.
Now run a wire from pin 87 to your accessory.
Finally, attach your accessories ground wire to any acceptable ground.
The best place to borrow power from is an unused ACC fuse terminal in the fuse
box.
If this is not available, an ACC fuse like the horn, cigarette lighter, or radio fuse
can be piggybacked with a fuse tap.
Pin 86 to ACC power.
Pin 85 to ground.
Pin 87 directly to the red wire on the switch box.
Pin 30 to positive post of battery.
If using part ACCEPSSWH0082 (model with 6 switches):
d.
e.
f.
g.
h.
i.
a.
b.
a.
b.
c.
d.
e.
A Brief Discussion of Relays:
What is a relay?
How a relay works.
Benets of a relay.
How to wire a relay.
NOTE: Relays come in many dierent shapes, sizes, and congurations. Always
verify pin location, function, and t of any relay you are planning to use.
1.
2.
3.
4.
a.
b.
a.
b.
a.
b.
c.
d.
e.
a.
b.
c.
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Optional Wiring:
87
87a
86
30
85
+
+
86
85 30
87a 87
Normally OFF Relay with a Positive Trigger
87
87a
86
30
85
DeviceDevice
To GroundTo Ground
To Positive
Trigger Source
To Positive
Trigger Source
To GroundTo Ground
To GroundTo Ground
FUSE
CUSTOMER’S SUPPLY
Leave DisconnectedLeave Disconnected
+
Battery
