Of course the problem is that is is grammatically a real puzzle:

The question popularly asked in court is "How do you plea?"
The answer is "I plead" innocent or guilty (at least in most cases.)

The proper form of past tense for "plea" would certainly be "pled" not "pleaed". If one considers the root to be "plea", then "pleaded" is some oddly redundant construction. If you consider "plead" to be the root, then "pleaded" may be correct.

Of course, the wrench in the works is that "plea" is a noun, the verb is "plead." While we have a general tendency to conjugate nouns (after all, I googled my way here), that doesn't make it correct.

However, when we look at similar verbs, we quickly see that the past tense of read is "read" (pronounced "red") and the past tense of "lead" is "led." If you add to that meet/met, feed/fed, and the like, it is hard to see any undue confusion here. Leaving the past tense of "plead" as "pled" directly conforms to the pattern of at least one other common verb, thereby following the rule, not creating yet another exception.

Then again, we could go with he rules of "tread" which is arguably the closest thing: that would mean that "plea" is gone in favor of "plead", and the past tense becomes "plod"; oops, that one's taken, too.

I humbly submit "pled" should be preferred above "pleaded" rather than adopting "leaded," which is how you spell the phonetic word "leded" (see lead[2].)