Favorite tools for troubleshooting electrical issues on John Deere

[Cliffbounder]

I've been chasing down a few electrical issues on John Deere machines lately, and it led to some good discussions in the shop.
I'm really curious about what tools you all trust whether it's meters, breakout boxes, software, test lights, or even your own homemade setups.
Which ones do you think actually help you save time instead of just adding to the confusion?

 

[Greenwrench]

After wasting a Saturday on a wiring issue, I whipped up a quick jumper harness and now keep a cheap test light in my pocket. With that and Deere Service Advisor, I can pinpoint issues much faster

 

[myBarnside]

Had a Deere that kept throwing random ghost codes after lunch breaks, so I finally decided to stop guessing and pulled out my meter and breakout box. It turned out that a loose ground was the source of all the drama. Simple tools, when used correctly, always outshine the fancy gear.