Temp Gauge and Tachometer

Today I set out to figure out why the temperature gauge wasn’t working.  I didn’t dare run the bike very far on the chance it might overheat.

In the end I think every electrical connection in the temperature gauge system was poor.  At first it looked like the sensor was bad (bad ground), then it looked like the 7V regulator wasn’t working.

Since I needed to debug the system anyway — literally –I pulled the tach off the bike so I could split the case.  Here’s the before with all of the dead spiders and the missing screw…

… and here’s the after.  The missing screw was rattling around inside.

I tested the temperature gauge on the bench using an adjustable power supply.  It worked just fine.  Then, it seemed like the 7V regulator wasn’t working,  I couldn’t measure 7V anywhere. I pulled it out and bench tested it as well.  It worked, but only when there was a load.   I used a small 12V box fan as a load and measure 6.95V.   Finally, after cleaning connections and putting everything back together, the entire temperature gauge system worked.

I’m still a bit suspicious of the sender unit.  It has a cold resistance of  7 kohm.  That’s higher than what you can find documented on the web.  Still, after starting the bike and letting it warm up, the temp gauge rose to the top of the narrow bar and stayed there.  So it seems to be working correctly, and it’s likely the thermostat opened up as well.