The circuit is fairly simple, and all parts are readily available. This gadget costs only a few bucks to make and is really useful. Be sure to use a fuse for the 0 Ohms setting, or you risk accidentally shorting something out!
The operation is fairly simple. Disconnect the sending unit for the gauge to be tested. Connect the tester instead of the sending unit. With the ignition in "run", check for the proper operation of the gauge. If the gauge is accurate, the sending unit is bad or you have a bad connection. Otherwise work towards the gauge and repair the wiring if necessary. If the reading is still incorrect at the gauge and the voltage at the gauge is present, the gauge is probably bad or has a bad contact. Remove it from the cluster and bench check before replacing.
Here are the correct readings for the various gauges:
| Setting | 1400 | 55 | 0 | 90 |
|---|---|---|---|---|
| Temp Gauge | 100F (cold) | 260F (hot) | - | - |
| Fuel Gauge | - | - | Empty | Full |
| Oil Gauge | - | - | 0 psi | 80 psi |