why are there diodes on my tc 29

[dqdave1]

When I removed side covers to replace a throttle cable I noticed one diode was kinda melted; so I am replacing it from Messicks. Why are diodes used here?

 

[dfkrug]

I imagine most of them are there to protect switches from inductive
currents. This happens when you switch off a coil, like when your
switch controls a solenoid or relay coil. Each time you switch off an
energized coil, you get a big spark across the switch contacts.

 

[jinman]

In addition to what Dave said, sometimes in control circuits where several different things can cause something to operate, diodes will be used for isolation so that a signal from one leg will not backfeed down the wrong line and cause improper operation in another circuit. We have several of these types of diodes on our tractors also. Do you have any idea what circuit it was in? Burned diodes are normally the symptom of a problem rather than the cause. Don't get me wrong, diodes can and do fail, but when you see a bad diode it is always good to do a thorough check of the other circuit components.

 

[dqdave1]

I did not trace circuit because the heated diode was probably due to corroded/oxidized connetors. They were corroded pretty well. I checked all other connections on all relays, diodes etc and most were clean and I used dielectric grease on all as i checked them. I also found that all the fuses in the fuse box in engine compartment had corroded also, so i changed out all fuses, useing dielectric grease.
This heated/melted diode was still functioning, just decided to replace it as a precautionary measure.