You need to get a service manual for your bike. Free downloadable one here:
Clymer manual here: http://www.themotorbookstore.com/kaw70vul19.html
I will give you testing info from my Clymer manual.
Fuel Gauge Testing
1. -remove seat
2. - disconnect fuel level sensor 2 pin electrical connector (1 white/yellow and 1black/yellow wire) at the end of the fuel tank.
3. -Turn ignition switch ON.
4. - Fuel gauge should read "E".
5. - With the connector end attached to the bike
(NOT the tank), use a jumper wire to momentarily
touch the two wires in the connector.
The gauge should read "F". Immediately disconnect the jumper wire. (Or you risk damage to the gauge).
6. -The gauge should read "E" again with the jumper disconnected.
7. - If the reading are correct the gauge is good.
8. - If readings above are correct, then the fuel level sensor in the tank or the wiring from the sensor to the two pin connector is faulty. Inspect wiring and/or replace sensor in tank.
9. - If readings are incorrect, fuel level gauge is faulty and must be replaced.
Temperature Gauge Testing
1. - Remove seat and tank.
2. - remove right-hand steering head cover.
3. - Disconnect yellow electrical connector from thermostat housing.
4. - Turn ignition switch "ON"
5. - Temp gauge should read "C".
6. - Attach a jumper wire to the yellow wire connector.
7. - Touch then immediately release
, the jumper to a good ground, like the thermostat housing. When the jumper is connected the gauge should read "H".
8. - Gauge should read "C" again, when disconnected.
9. - If readings correct the gauge is good, but the coolant sensor may be faulty. Inspect sensor.
10. - If temp gauge reading in steps 7 & 8 are incorrect, either the gauge or the wire between the sensor and the wiring connector is faulty. Inspect wiring and/or check the coolant temp sensor.
Coolant Temperature Sensor Removal/Testing/Installation
1. - Remove tank.
2. - partially drain cooling system, just enough to lower coolant level below upper hose. this lessens spillage onto front cylinder head.
3. - Disconnect wire from sensor.
4. - Unscrew sensor from thermostat housing.
You will now need a shop thermometer that reads higher than 212*F, an ohm meter and a pan of coolant to suspend the sensor threads in while you heat it up on a stove burner. Do not let the sensor or thermometer touch the pan or the readings will not be accurate.
At room temp the ohm meter should show no continuity of the sensor, (infinite resistance) between the terminal on top and grounding it on the side.
Heat slowly to 80*C (176*F). Should be 42-62 ohms of resistance
Continue heating to 100*C (212*F). Should reduce to 22-33 ohms resistance.
turn off heat.
If sensor fails either of these tests, it must be replaced.
When cool, remove sensor from pan and apply silicone sealant to threads, install and tighten securely.
Attach connector to sensor. Make sure the connection is tight and free of oil and corrosion. (use some dielectric grease to seal and protect)
Refill cooling system.
I hope you can follow this, without benefit of pictures from the book.
Let us know what you discover from these tests.
I believe I will let someone else help you with the neutral light, as there are several connectors in the headlight bucket that must be disconnected, and the whole speedo, tach, indicator light assembly comes off.