Water Temperature Gauge, Manual Fan Switch, and Fan-On LED Indicator Installation

The bike, especially in unrejetted stock form, generates quite alot of heat. The designers could have decided to include a water temperature gauge but chose instead to give us a warning light. The thermostatically controlled fan also disconnects the rider from positive control over the cooling process. A manual fan switch restores that ability. In hot, slow riding in traffic the thermostat triggers the fan a bit late and then stays on for a long time. This page describes the installation of a water temperature gauge, a manual fan switch override, and an LED indicator to display when the fan is running. The running fan is a bit of a battery drain so the fan should not be left on too long.

The water temperature gauge selected is an analog electrical type from Auto Meter. Available mechanical gauges require the use of six feet of capillary tubing, somewhat of a difficulty on a motorcycle where space is at a premium. Also, I would have preferred to use a liquid filled gauge to dampen vibrations on the needle but this was not available on an electric gauge and actually turned out not to be necessary. This analog gauge requires 12 volts and is powered from the bike's electrical system. It should be wired to be on only when the ignition is on so it will not register unless the bike is running. Replaceable batteries are also not a concern with this installation.

The gauge is mounted on the right fairing insert along with the manual fan switch and the LED. This means that you must remove your hand from the throttle to actuate the switch. This should not be a limitation since when you are rolling along at speed there is no need for the fan to be switched on. Also, you should not be taking your hands off the handlebars during cruise anyway.

The temperature sending unit is provided with the gauge and a nicely designed adapter was fabricated and supplied by Ron Ernst. My thanks to Ron for all the help he gave to me during the course of this project. Thanks most of all to my Dad who did most of the installation work during my period of singlehandedness.

I used a three-position switch (ON-OFF-ON) to enable selection of the normal automatic thermostat controlled mode, fan ON manual override, and a fan OFF manual override position.

The indicator LED comes on whenever the fan is operating regardless if enabled with the thermostat or turned on with the manual override switch.

The cost of materials for this project was about $100.

  • Water Temperature Gauge, Auto Meter Phantom Model Number 5737 - $39.95 (plus shipping) from Summit Racing.
  • Angle Ring, set of three for $7.00 from Summit Racing.
  • Sending Unit Adapter from Ron Ernst. Please contact Ron for pricing and availability.
  • Three Position Switch - about $2.50
  • LED with Integrated Resistor and Holder- about $3.50
  • Miscellaneous - Wire, Lots of Connectors, Hole Saw, Hose Clamps, etc.

The labor time required depends on how quickly you feel comfortable proceeding. I went very slowly.

I did this installation when my fuel tank, fairing inserts, and side covers were already off the bike. The fuel tank doesn't have to be removed, just lifted out of the way. At some point during the installation you will need to:

  • Remove left side cover, one large Phillips screw.
  • Remove the right fairing insert.
  • Lift and prop up the fuel tank. Turn fuel petcock to OFF for safety.

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The sections below are:

  1. Fabricate the Wiring
  2. Install Adapter and Sending Unit
  3. Install Water Temperature Gauge
  4. Install the Fan Switch and LED
  5. Connect the Wiring
  6. Installed Pictures
  7. Testing and Results

1. Fabricate the Wiring:

A number of wiring connectors should be made to faciltate all the connections that are required. I used 14 gauge wiring for these connectors. I would use a smaller gauge wire a second time to make it easier to make all the connecting wires with the crimped connectors. I'm not very good at making reliable and strong connectors.

The best place I found to tap into the existing wiring for the manual fan switch was at the fan relay. This is located under the left side cover. This is also a good source of +12 Volts for the temperature gauge as it is on the same side of the fan relay fuse. The hot lead to the fan also starts here and can be tapped into for the fan-on indicator LED.

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The first image below is an overview wiring diagram showing the connections for installing all the components. The second diagram shows the details of tapping into the fan relay wiring without cutting the stock wires. The red, blue, green, and black wires at the bottom of the first diagram are the same as the red, blue, green, and black wires at the left of the second image.

The Auto Meter gauge does not come with wiring and you must fabricate your own. The eyelets I used were too large at 1/4" but they did work. Smaller ones would fit more snugly around the terminals. The indicator LED wires are soldered onto the LED and taped together. An excellent chassis ground location was selected under the tank just above the location of the sending unit adapter (see below). This takes advantage of the removed Air Induction System (AIS). A wiring bus was made to handle the three ground plugs.

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This is the wiring bus for the connection to the fan relay. Four wires about 42" in length are used.

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Rather than cut into the stock wiring I made these connecting wires that plug into the wiring bus above, the fan relay plug, and the fan relay. The right image shows the same connector as the rightmost one in the left image. There are five connectors.

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Here are the wires connected to the fan switch and to the LED. On the LED, the slightly longer lead is the anode or + lead, the shorter is the cathode or - lead. The fan switch wiring is the same one as shown in a picture above.

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2. Install Adapter and Sending Unit:

As mentioned above, the sending unit adapter is available from Ron Ernst. I got mine from Ron on ebay. Those having access to a lathe and milling machine and wishing to fabricate the adapter can do so themselves. Start with a 2" OD piece of T6061 aluminum round bar, cut it to 3" in length, bore out the inside to 15/16", turn down each end to 1.1" about 1" in length and then tap the center section for a 1/8" NPT thread. The place to mount the adapter is in the middle of the upper radiator hose. This puts the temperature sensor directly in the coolant flow ahead of the thermostat. To do that you must take off that hose, cut about 1" from the center and insert the adapter and secure with hose clamps.

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Detailed installation steps are:

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  • Remove Thermostat Attachment Bolt. This permits thermostat to move, easing removal of upper radiator hose.

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  • Loosen Upper Radiator Hose Clamps.
  • Pry Off Upper Radiator Hose.

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  • Test Fit Adapter. The 3" long adapter appears to be too long to fit but the thermostat will rotate out a bit for a little extra room. Others have successfully installed the adapter as is but I had difficulty and elected to trim 1/4" from each end with a hacksaw and smoothed the ends with a file. My apologies to Ron for defacing his work.

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  • Cut Radiator Hose Pieces and Attach to Adapter. I cut 1 7/8" from each end of the hose. The rubber sleeve brace is glued on and pulls right off to ease the cutting. A sharp knife is the best cutting tool. 3/4" - 1 3/4" Hose clamps secures the hose to the adapter.

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  • Install Adapter. The adapter is oriented such that the sending unit points forward to permit ease of tightening and installation of the wiring.

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  • Attach Sending Unit then the temperature sensor wire. I initially had attached a separate ground wire to the body of the sending unit because Auto Meter technical assistance had assured me that this connection was required. However, I found that I had electrical continuity between the body of the adapter (and therefore the body of the sending unit) and the bike's chassis ground. I suspect the adapter is contacting the stock coolant pipes under the coolant hose. I decided to leave the ground wire off for a cleaner installation. If there was no electrical continuity between the sensor's body and ground then a separate ground wire should be necessary.

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  • Re-Attach Thermostat Attachment Bolt.
  • Re-Attach Radiator Overflow Hose.
  • Top-Off Coolant.

3. Install Water Temperature Gauge:

Shown here are some of the gauge components. The hole saw is not supplied with the gauge.

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I chose the Phantom Type Gauge face. Here are a few alternate gauge face options. The center gauge has a carbon fiber look face.

Precise placement of the water temperature gauge on the right fairing insert is critical. The fairing support bracket interferes underneath and the radiator filler cap also intrudes. The bracket position is adjustable so position it as far forward as possible to ensure the gauge will clear with the bracket as far forward as it will go.

Remove Fairing Support Bracket from Bike and Attach to Fairing Insert.

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Position Hole Saw Underneath and Drill Pilot Hole with Arbor. The hole saw is a bit larger than the gauge and serves as a guide for placement.

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Shape the bottom of the angle ring with a Dremel tool so it follows the contours of the top of the fairing insert at the ring's mounted angle. Then mount the angle ring and water temperature gauge. A rubber washer ring cut from sheet rubber forms a more secure mount for the aluminum bracket underneath which was cut shorter and the feet angle cut to match the base. Black silicone sealant fills in any gaps in between the angle ring and fairing insert on top. Wipe off any excess.

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These show the fan switch and LED already in place but they are actually installed in the next step.

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4. Install the Fan Switch and LED:

The LED has an integrated resistor so there are no current limiting issues. The center position of the fan switch will be for the fan always off.

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Position and Drill the Holes for the Switch and LED. Reposition the mounting bracket underneath the fairing insert as far back as it will go to ensure clearance.

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5. Connect the Wiring:

Route Fan Relay Connecting Harness.

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Connect Wires at Fan Relay

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Connect Wires Under Fairing Insert and Route To Under Tank Area.

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I connected the fan switch so that the manual mode is the switch depressed to the right. It doesn't matter.

The under tank connections are messy and will require undoing most of them to remove the right fairing insert. I will later try to install a better looking multi-pin connector to improve the appearance, reliability, and function.

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A possible idea for improvement is to recognize that there are three wires that come from the fairing insert that all go to ground. They could be connected together under the fairing insert and then two fewer wires would come into the under tank area.

6. Installed Pictures:

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Here is an alternate installation from Uri in Israel.

7. Testing and Results:

Set the fuel petcock back to ON, lower and secure the tank, reinstall left side cover. Then go for a ride and test the function of the gauge, switch positions, and LED. Watch also for leaks from the water hose adapter. It also remains to be seen if the switch and LED are sufficiently water resistant.

The LED does wash out in direct sunlight but can be seen when shaded.

The needle is well damped and rock steady. A liquid filled gauge is not necessary.

Keep in mind when evaluating the results below that my bike has been rejetted with Ivan's kit and hence tends to run a bit cooler than stock.

According to the Service Manual the thermostat starts to open at 160 degrees and should be fully open at 175 degrees. The thermo switch turns on the fan on at about 230 degrees and will then switch the fan off at 215 degrees. The temperature warning light comes on at 260 degrees.

Another excellent web page on manual fan switch installation can be found here.


The Auto Meter gauge is not very waterproof. A simple hosing down of the bike produced this leakage.

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Fortunately, the fluid evaporates in just a few hours.

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Last Updated: 03-26-2005

Copyright © 2001-03, Patrick Glenn, All Rights Reserved.
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The information presented here reflects solely my personal experience with my motorcycle and is presented for entertainment purposes only. No information presented here is to be relied upon for issues of rider safety nor to replace the services of a qualified service technician. Any attempts to follow or duplicate any of these procedures are done so completely at your own risk. By reading the information on this site, you agree to assume complete responsibility for any and all actual or consequential damages that may arise from any information presented herein.