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Low Fuel Light level adjustment & sensor repair ( ST1100 ) *

Started by KoTAOW, December 20, 2007, 05:04:10 PM

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Low Fuel Light level adjustment

To make the light come on at a more reasonable amount of fuel remaining:

1. Drain the tank.

2. Disconnect the wires to the fuel pump and warning light (top of tank) and the wire to the sender (left side of tank about 1/2 way down).

3. Disconnect fuel cap breather hose, fuel line at the filter.

4. Remove the four bolts holding the tank in from the top.

5. Lift out the tank by sliding toward the rear while lifting (if you have trouble, loosen the air cleaner, but we removed the tank on both of our, 93 & 94, STs without doing this)

6. With the tank out of the bike you can remove both the fuel pump and light sensor from the top, and the fuel gauge sender from the left side.

7. Actually, you can remove the warning light sensor without pulling the tank, but you must pull the tank to get at the fuel gauge sender on the side. The

STock fuel gauge on our STs was very inaccurate from the factory. The gauge stayed on full, without moving for 100 miles. It then descended fairly linearly until it touched the bottom peg on the gauge where it still had about 50 miles before actually being empty of fuel.

8. To change the low fuel sensor so that it comes on with .8 gal remaining (instead of STock 1.4 gal), remove the small philips screw holding the sensor to the fuel pump mounting bracket. Drill a small hole, the same diameter as the STock mounting hole, 1/2" farther down the mount than the STock hole. Then remount the sensor at this new location, and your low fuel light will now indicate when you have 30-40 miles left (in our case....YMMV ;-}

Now the real reason to go to all of this trouble in the first adjust the gauge sender so that you fuel gauge more accurately represents what fuel is actually in the tank:

10. When you remove the sender from the left side of the tank, you will see a float on the end of a long piece of bent metal rod.

11. The idea is to "adjust" this rod so that the float will travel the full distance from the top of the tank to the bottom. In our case, the STock float stopped before touching the top or the bottom of the tank.

12. There are limit tangs on the sender itself that keep the rod from traveling the full distance necessary top to bottom of the tank.

13. By bending the tangs and the rod you will be able to fine tune the sender so the gauge will indicate, in a linear fashion, the true level of the fuel tank while the fuel is between the top and the bottom of the tank.

14. Here's the "catch" will see when you have the tank out, that it is not linear in shape from top to bottom. IOW, there is no way to get the gauge sender to travel up into the "top stack" area or the "sump" area on the bottom of the tank. So your gauge will still rest on the top peg until the fuel drops to the bottom of the "top stack" where the sender float can read it (.85 gal or appx 30 miles in our case). Also when the fuel reaches the bottom of the tank, and the float bottoms out, the gauge will rest on the bottom peg and there is still .8 gal of fuel in the sump (where the fuel pump lives). I've never run totally out of fuel (I've added 7.5 gal at the "pump" on 1 or 2 instances 8>0 , but I filled the tank after this mod using a graduated beaker. Here are the results of my measurements as I added fuel to the TOTALLY DRY tank with the "modified" gauge and light:

.8 gal........ gauge on bottom peg...light first on steady
1.5 gal...... gauge on red mark...light first starts to flicker
2.0 gal ......gauge at bottom white mark
6.4 gal ......gauge at top white mark
6.9 gal ......gauge on top peg
7.5 gal.......fuel at bottom of fill tube
7.75 gal.....fuel at very top of fill tube (my tube is modified to allow easily doing this if I desire)

I have done over 40,000 miles on my bike since I did this mod and have had no problems with the gauge or sender due to its wider range of travel, YMMV of course. Also, this mod requires handling flammable liquid and carelessness could result in you and your beloved ST catching fire. If you are uncomfortable with this fugedda 'bout it


ST1100 Low Fuel Sensor Repair

There are several articles in regards to repairing the low fuel sensor on Honda Goldwings and V-65's on the internet.  
The ST1100 uses almost the exact same setup and therefor these articles can be used to also repair the ST1100.
Taken from GWRRA Message Board Achieves ( February 2002):

The V-65 low fuel sensor has a little canister that's soldered to a threaded
plug with a Bakelite insulator in the center. I carefully desoldered the
canister and the center conductor from the threaded plug. Then I removed the
fuel pump assembly from the Gold Wing's fuel tank. I removed the screw from the
electrical connector near the top of the fuel pump mounting bracket and the
two screws that hold the sensor assembly to the lower part of the pump assembly,
just above the pump. I desoldered the old sensor from the little screw-on
bracket and cut the wire about 3/8" from the top of the sensor. I stripped about
1/8" of insulation from the wire that I cut and tinned the bare wire with
solder. Then I soldered the wire to the replacement sensor and tack-soldered the
replacement sensor to the little screw-on bracket. I soldered the tinned end of
the wire to the center terminal of the replacement sensor.

I decided to run another dynamic test on the rebuilt sensor assembly. It passed
both static (ohmmeter) and dynamic tests. Then I mounted the rebuilt sensor to
the fuel pump assembly and reinstalled the fuel pump assembly to the Gold Wing.
I still had a slight doubt whether this repair would be successful, so I drained
the fuel tank down to a little over a gallon. I took the Gold Wing for a road
test, and just as the needle on the gauge lined up with the red mark, the
indicator light started coming on! Now I was satisfied that the repair job was a
success! I learned that with a little soldering skill, I could use a Honda V-65
Magna low fuel sensor, Honda part no. 37810-MB4-008 for a Honda GL 1500 low fuel
sensor, which has NO HONDA PART NUMBER and save myself about $200.00!

If your GL 1500 Gold Wing is still under warranty and your reserve indicator
malfunctions, take the Gold Wing to your Honda Dealer and they'll probably
replace your fuel pump free from charge. But, if your GL 1500 is not covered by
the warranty any more, you too can save a few dollars by buying a V-65 Magna
sensor (for about $48.03) and, with a little soldering skill, fix it yourself!
By Howard Halasc on Saturday, February 16, 2002 - 5:45 pm
In the May issue of Wing World Magazine, I tried to explain how to save money to
get a malfunctioning reserve indicator working again without spending a lot of
money for a new fuel pump on the GL 1500 Gold Wings.

One problem is that most Honda dealers don't stock the V 65 Magna sensor and
most salvage yards don't have any good ones that haven't corroded or gone bad
from soaking in old spoiled gasoline.

After doing a little bit of research, I found out that the sensor is actually a
thermistor that is rated at 1,000 ohms at 25 degrees Celsius. These little
thermistors come in two different types-PTC and NTC. What our Gold Wings use is
the NTC, which decreases resistance as temperature increases. It is in a series
circuit with the indicator bulb. As long as the thermistor is submerged in
gasoline, it remains cool and the resistance to the flow of electrons is
anywhere between 900 and 1200 ohms, depending on the temperature of the
gasoline. When the gasoline level drops below the level of the thermistor, the
current flow through the thermistor and the light bulb causes the thermistor to
heat up and drop its resistance, thus illuminating the bulb. Damage to the
thermistor is likely to occur if you refuel with the ignition key on and the
reserve indicator illuminated. When the cold fuel comes in contact with a hot
thermistor, the sudden temperature change permanently damages the thermistor.
My advice is to turn your key to the off position when you refuel. This advice
applies to all motorcycles, not just Gold Wings.

The article in the May issue of Wing World also applies to the GL 1200
Interstates and Aspencades. Here again, there's no Honda part number for the
reserve indicator sensor and the sensor is part of the fuel level sending unit
on the GL 1200I's and GL 1200A's.

At one time, Radio Shack sold various thermistors, but the last time I checked,
they told me that they no longer stock them. I bought some from Ace Electronics
here in Houston and they cost $1.00 each. The V65 Magna sensors can be repaired
by installing a new thermistor in the little canister, but the GL 1500
canisters are sealed and difficult to open up for thermistor replacement. By the way, I wrote articles about
this topic and they appeared in the May and July 1998 issues of Wing World.

Howard Halasz, WING WORLD contributing editor


Taken from:

The low fuel sensor...p/n 37810-MN5-008...or can use the one from a V65 Magna...p/n 37810-MB4-008..
The part number for the 1200 and 1500 low fuel sensor is 37810-MN5-008. They are $30.11
Note that this is the Honda part number, the other one is available from elec supply house.
I use the same thermistor in the GL1200 and the GL1500. The low "fuel sensor" is a NTC THERMISTOR.
Part number 20F735 TYPE RL2004-582-97-T10 $2.82  If you are in the US call 1-800-463-9275.

If You are in CANADA, email me and I will find the canadian phone number.
The thermistor is in a little can about the size of your finger. It is soldered to a wire on one end and to the can on the other. Some guys cut the can open but I have been drilling out the spot welds and pushing the can back together. I then punch it in 3 places to hold it together. From talking with others, I find that the can is not the same on all models. It is pretty simple stuff anyway. You are not really adapting anything. It is physically almost identical to the part used by Honda. Electronically, it is identical. Just carefully bend the leads and cut to length to match the original. Hold the leads with small needle nose pliers close to the thermistor so as not to fracture it while bending.


( 1 K ohm ) thermistors on-line from Mouser Electronics ( ) for $5.80 plus
$3.67 shipping + handling for a total of $9.47 or about $1.89 each.

The part number is: 527-2004-1k or a link to the data sheet is:

Contributed by:  Tom Melnik, STOC @346


Fuel system wiring schematic provided by Tom Melnik.

Fuel System Wiring ( PDF )

Pictures provided by Carroll Walker.


Taken from Mike Martin's web page:

Fuel Light Malfunction

Marc Newman wrote: "I filled my tank this morning, and right as I was parking at work the fuel light came on. Turned it off and on and the light went out. Tonight, the fuel level showed full but the light was blinking on and off, mostly on. Any ideas?"

Don Home was kind enough to provide the following write-up:

A quick test of the low fuel light circuit is to short circuit the sensor connector (the Brown with Blue striped wire lug next to the green wire ground lug on top of the fuel pump assembly located under the seat) to ground with a screwdriver or knife blade with the ignition key on. If your fuel light comes on, the bulb and circuit wiring are OK. Just be sure you short the BROWN with BLUE striped wire and NOT the brown with red striped wire which is the 12vdc power to the pump!

Since your light is staying on, the easiest way to check would be to disconnect the Brown with Blue striped connector at the fuel pump when the light is staying on with a full tank. If the light goes out, then the problem is a short in the sensor or wire leading to the sensor on the fuel pump assembly. If the light stays on, then you may have a short in the Brown with Blue striped wire back towards the indicator light, or a problem in the "LAMP CHECK UNIT" which grounds the Brown with Blue striped wire for a few seconds when you first turn on the ignition switch. Disconnecting the "LAMP CHECK UNIT" from the circuit will further pinpoint the problem to the wiring or the "LAMP CHECK UNIT". I'm not sure where the "LAMP CHECK UNIT" is located, but I can look it up in the service manual if you need to know.

An ohmmeter check of the sensor should read greater than 1,350 ohms with the fuel in the tank above the sensor and 0 ohms when the fuel is below the sensor (<1.4 gal). My defective sensor read over 6,000 ohms with fuel over the sensor and without fuel and would not light the low fuel bulb! The sensor is part of the pump assembly and costs around $300 to replace. Luckily, mine was still under warranty when it went bad. The sensor itself is attached to the fuel pump pickup tube with screws and changes resistance with being wet or dry. All of these test pertain to my 1999 ABS and should be valid for your 2000 model.