* Subject-verb agreement: The verb in a sentence must agree with its subject in number.
* "Either...or" constructions usually require a singular verb when the subjects are singular.
The correct sentence would be:
* "Either you or I am wrong."
Since "you" and "I" are both singular pronouns, the verb "am" (singular) agrees with them.
Here's another way to look at it:
If you were to separate the sentence into two clauses:
* "You are wrong."
* "I am wrong."
The verb "am" would be the correct choice in both cases.