Understanding Gas Gauge Operation

[xxBenJamminxx]

Ok I wanted to make sure I have some things straight. First off I am trying to fix the gas gauge on my 82 GS550L. Its stuck on full and never moves, even when turned off, but was at 1/3 when I got the bike 3 months back. This leads me to believe that the gauge itself works, and its just something with the wiring and/or sending unit.

Here is where I want my work double checked to make sure I am understanding where I am so far. With the tank unplugged I tested the leads for Resistance and get infinite ohms the few times I checked it with different levels of fuel. So I am thinking that the sending unit is either shot or at the very least needs attention like I seen a thread around about adjusting the wiper to make better contact inside the sending unit itself.

Now with it showing infinite ohms that should make the gas gauge itself go to the EMPTY position since the ohms increase as the float drops. Am I thinking right there? or is lack of a circuit there just freeze the needle where ever it is at?

2. Should the gas needle drop to empty whenever the key is turned off?

3. Where are the wires that I can jump to see if the needle moves or not? I found a 3 wire plug that looks similar to the service manual but the wires go the kill switch on the handlebar.

4. Here is a picture of the back of my cluster. The 3 wires going to the screws are directly behind the gas gauge. Does anyone know what each wire is for and where they go?

Im thinking for the wires: Orange- Power from ignition? Blk/Wht- Ground Ylw/Blk- Sending unit?



I did a little testing too and this where it confuses me most. Testing on the Ohm setting at 200k I think, when testing the blk/wht wire at tank connections on the bikes side of the harness and the blk/wht wire at the gas gauge I get infinite ohms. With key on and on 20V DC I dont get any voltage across any of the 3 wires at the gas gauge. Shouldnt there be power there?

Im not the greatest at electrical stuff by any means so very well may be doing something wrong. Sorry its so long but wanted to be detailed and provide all the info I could. I searched but can not find the stuff I was looking for and thought this may help future troubleshooters.

Thanks in advance

 

[chuck hahn]

Its fed thru the rehistat in the sending unit.

The slider arm inside the sending unit slips along the waffle board coils and this regulates the volts that are sent to the gauge.

The needle moves by a bimetal strip that heats up according to the voltage that the sending unit allows thru..the fuller the tank the more voltage..thus the hotter the bimetal strip gets and flexes more..follow me?

Take a jumper and go between the wires off the harness..should go to full with the key on..give it a few seconds to get there. remove jumper and it should go to E. If this checks out, you've got a sending unit that's cruddy and needs some attention under the cover. See Bikecliffs welcome site for the sending unit repair tutorials.

 

[posplayr]

Its fed thru the rehistat in the sending unit.

The slider arm inside the sending unit slips along the waffle board coils and this regulates the volts that are sent to the gauge.

The needle moves by a bimetal strip that heats up according to the voltage that the sending unit allows thru..the fuller the tank the more voltage..thus the hotter the bimetal strip gets and flexes more..follow me?

Take a jumper and go between the wires off the harness..should go to full with the key on..give it a few seconds to get there. remove jumper and it should go to E. If this checks out, you've got a sending unit that's cruddy and needs some attention under the cover. See Bikecliffs welcome site for the sending unit repair tutorials.

Not sure exactly what gauge we are talking about but there was a switch from bimetallic type gauges to a magnetic movement. It should be described in the manual. My ED uses this style for both fuel and temp. There is. Current balance based on a voltage divider where the the gauge sensor form part of the divider circuit. Details in manual.

 

[xxBenJamminxx]

So is the gas gauge suppose to drop to empty whenever the key is shut off or does it remain in the last registered position?

Is the white plug with the 3 wires coming out of it on the bottom of the picture the one I should be using the jumper on? It has an Orange wire, yellow/blk and a blk/wht wire going into and coming out of it. Why does it seem to run up to the kill switch on the handlebars if that is the one for the gauge?

Should there be power registering at the back of the gauge where the 3 wires attach to the bolts?

Thanks for the help so far guys. Also any ideas on how I can test the wiring between the gauge and the tank connectors with my meter?