17
Relays and Switches
All ACCESSORY wires found in this harness can support up to 15 amps.
Components requiring more amperage will need to be connected to a relay. An
ACCESSORY wire can be used as a 12 volt activation source or 12 volt source for
ground activation in these circumstances. Take a look at Painless part #’s 30107 &
30108 to fill your relay needs.
A 12 volt activated relay is constantly grounded and will send power out of the
output side of the relay to the component being powered when 12 volts is applied to the
relay, as the name implies. The 12 volt source can be wired directly to the relay or
interrupted by a switch, as shown in the 12 VOLT SOURCE ACTIVATION drawing.
Wiring directly to the relay, as indicated by the dashed line, would be used in the
case of wiring a water pump relay, or any other high amperage component you
would want to run continuously while the key is in the on position. In these cases,
make certain the 12 volt wire you are using is an Ignition Switched 12 volt wire and
not a battery constant hot.
The 12 volt activation wire can also be wired to a switch to offer the user OFF/ON
capabilities. These are the situations a battery constant power source would be
used. This would allow a component to be turned OFF or ON without the key in the
ON position. However, unless a lighted switch is being used, a ground activated
relay may work better to avoid running power through the switch.
A ground activated relay is just the opposite of the 12 volt activated relay, 12
volts (battery constant or switched) is supplied uninterrupted and the ground wire is
switched. The Horn Relay pre-wired in the Painless harness is a Ground Activated
Relay. Another example of this method is a thermostat operated fan relay. In this case
however, a thermostatic switch would replace the switch in the drawing below. Like
mentioned before, ground activation method is best used when a component is
operated by an unlit switch from the interior of the vehicle.
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