tach troubles

This morning I fired the truck up and almost immediately got the buzzer and red triangle and message about my tachometer messing up.
The problem would come and go and sometimes the tach would work and other times it was dead.
Everytime I tried to run it thru the gauge diagnostics ( where it makes all the gauges go through their full sweep) it would kick the warnings on before it completed the test.
I looked at the diagnostics and it said that the rpm info going to the ECU was erratic.
At this point I didn't know if I had loose wires in my dash, which I've had apart a number of times, or out under the hood. I wiggled the wires on the ECU but that didn't help. This is on a Cummins ISX.
After asking God to help me get this figured out quickly and inexpensively I decided to pull the wires off the ECU and found out there was no corrosion or anything.
I then looked at the top center sensor that is to the right of the ECU and it was quite oily and dirty on the outside so I unplugged it. Turns out it had a teaspoon of oil inside of the connection. I broke out the Brakleen and sprayed both parts and put her back together.
Voila! No more troubles.
So if you have these issues, you know where to look.

 

On my motor the three pin connector that I disconnected and cleaned is the upper sensor , a two wire one that I didn't touch is below that. I have noticed that my engine brake has acted funny a couple times in the past though.
I just ran 1800 miles without a hiccup since I cleaned that sensor.