MBDoc is absolutely right.. I have seen this on many of my cars, and it is always one of two things:

Overvoltage protection relay
-OR-
Battery

The OVP relay is a known cause of this problem, and it has a 10A GM-style fuse in the top of it.

Battery getting old is also a common cause.

I used to troubleshoot these issues, but now here's what I do. For a total cost of $100-150 (depending on the battery), I buy a brand new OVP and battery.

Unless your OVP or battery are less than a couple of years old, just buy new and you'll fix the problem forever. There is no point in trying to spend $$$ troubleshooting this type of issues when 90% of the problems are solved by spending the $100-150.

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