A few miscellaneous items to discuss, Starter switch cleaning, VSS (vehicle Speed Sensor), low fuel indicator sensor.
Starter Switch has full time headlight current going through it, about 5 amps. Dirt + grease plus time and it creates resistance on the contacts which creates heat. Plastic may melt, shunt gets stuck, cannot bridge/close contacts, headlight and/or trying to crank engine fails.. Usually a cleaning restores the Starter Switch. Sometimes the shunt spring has to be stretched and the shunt may require a slight bend or trimming of plastic which could be preventing shunt movement. http://www.rattlebars.com/mtz/starter.html
Great info at that site.
VSS is a sensor near a transmission gear tooth and it outputs +5v pulses when the rear wheel is turned. I measured between 68-72 pulses per revolution.
Usually the actual voltage is 3.5 volts. The 1800 has a much higher failure rate than the 1300, same part.
If the pulses are crappy the speedo/odometer may work intermittently and then normally it gets worse. Sometimes the VSS signal is missing or extremely crappy then the ECM will put it in "Failsafe" mode.
Low Fuel indicator - is a thermistor(special resistor) that when in fuel it has a high resistance(1k) and no bulb or led will light.
When it is in air the thermistor begins heating from current flow and the resistance lowers, the bulb gets brighter.
A few thermistors with led indicators have worked well in the repair, but the 1800C with a light bulb drawing more current was a problem to solve.
Putting two in parallel did not help, two thermistors in series worked. The OEM thermistor appears to be larger than the replacement therefore
more current capacity. Nascarpop with the in series thermistor project. Toboggan with the Led indicator. Both used same part#.