Hey guys out 07 s40 has developed some kind of problem. It was running fine and all at one noticed the lights on the radio and heater controls were flickering. It went away for a day then started doing it again only this time it wouldn't crank like a dead battery. Battery was fine though. Kept hitting the key and it started. Doing the same thing but runs fine. I checked the battery cables but they are good. do these have any other grounds that are a common problem to take a look at? Possible ignition switch? Any ideas or places to check feel free to comment. Thanks

 

Sounds like a bad connection / cable issue I'd suggest using a voltmeter to find out where the voltage disappears when the issue is happening. Just start at the battery, and probe across every point between the battery terminal and the starter. When you get to the one where the voltage drops, the problem is between that point and the last good point you checked. Of course, this test only works when the failure mode is happening, and you'll need a helper to turn the key. Make sure and check between the battery terminal and the battery cable clamps (a very common source of a flaky connection). A rule of thumb is that if you can twist the clamps, they're WAY too loose.

Check the negative side as well (probe from the battery negative terminal to the engine block - if there more than a small fraction of a volt, you have a bad ground cable).

 

I did finally get it figured out. Ended up being the positive cable on the starter was very rusty. I had the remove the air box to get to it and that was a complete bear. I have never struggled so much just to remove an air box.