Lexus V8 Electric Fans Kit Relay Wiring Diagram

UPDATE: July 2, 2020 A limited supply of original Lextreme parts back in stock including EGR Delete Kits, torque converters, supercharger brackets, etc! Please note that the SC400 turbo kit is all sold out and won't return. Email me at [email protected] which original Lextreme parts you need and I'll check availability. (Please note that we're not an auto parts supplier.)

LEXUS 1UZFE MODS FORUMS - Post Questions Here For Quick Answers!


SPDT Relay  : (Single Pole Double Throw Relay) an electromagnetic switch, consist of a coil (terminals 85 & 86), 1 common terminal (30), 1 normally closed terminal (87a), and one normally open terminal (87).In our application:

 (Yellow) Power Positive (+)
86 (Black) Ignition Switch (+)
30 (Blue Wire) Out put to Fan (+)
85 (White) Ground from Temperature Sensor (-)
87A Is not being used in our application.


Each fan will get its own relay to eliminate over heating.  From my personal experience, one relay per fan.  The relays would be wired together with the exception of Number 30 (Blue Wire).  Each blue wire from the relays should connect to the fan and other of wire from the fan will be ground (get negative from the frame).

When the coil of the relay is at rest (not energized), the common terminal (30) and the normally closed terminal (87a) have continuity. When the coil is energized, the common terminal (30) and the normally open terminal (87) have continuity.

The diagram above center shows the relay at rest, with the coil not energized. The diagram above right shows the relay with the coil energized. As you can see the coil is an electromagnet that causes the arm that is always connected to the common (30) to pivot when energized whereby contact is broken from the normally closed terminal (87a) and made with the normally open terminal (87).

When energizing the coil of a relay, polarity of the coil does not matter unless there is a diode across the coil. If a diode is not present, you may attach positive voltage to either terminal of the coil and negative voltage to the other, otherwise you must connect positive to the side of the coil that the cathode side (side with stripe) of the diode is connected and negative to side of the coil that the anode side of the diode is connected.

Diodes are most often used across the coil to provide a path for current when the current path to the relay is interrupted (i.e. switched off, coil no longer energized). This allows the coil field to collapse without the voltage spike that would otherwise be generated. The diode protects switch or relay contacts and other circuits that may be sensitive to voltage spikes.

Why do I want to use a relay and do I really need to? Anytime you want to switch a device which draws more current than is provided by an output of a switch or component you’ll need to use a relay. The coil of an SPDT relay that we most commonly use draws very little current (less than 200 milliamps) and the amount of current that you can pass through a relay’s common, normally closed, and normally open contacts will handle up to 30 or 40 amps.

This allows you to switch devices such as headlights, parking lights, horns, etc., with low amperage outputs such as those found on keyless entry and alarm systems, and other components. In some cases you may need to switch multiple things at the same time using one output. A single output connected to multiple relays will allow you to open continuity and/or close continuity simultaneously on multiple wires.

Do you have any questions? If so, please head over to the forums to get a quick answer or share your experience!

This is a freelance site with no support by huge companies.  I have been doing most of the R&D and technical write-ups by myself with my personal money and literally thousands of hours of my time.  I have taken extra steps to demonstrate in details how things are done.  Currently I am one of the few people doing Lexus V8 research and performance enhancement.  This effort comes from my personal love for this wonderful engine.  Most of the modifications are from trial and error. There's no cookbook for 1UZFE mods and its unknown territory for much of supercharger performance.  The parts, labor, web development and site hosting are 100% paid from my personal hobby money.  If you feel my efforts help you in any form, please do not hesitate to donate any amount of money to support this site. You have no idea how much I and the entire Lexus and Toyota community appreciate it!

Leave a Reply

Your email address will not be published. Required fields are marked *