Where in the constitution is the electoral college described (there are 2 parts) ?

The Electoral College is found in Article 2, Section 1, and in the 12th Amendment.

The 12th amendment had to be added because there was some misinterpretation of the constitution and politicians were exploiting the fact that it wasn't completely defined in the constitution. It was ratified in 1804 and since it was added the article 2 section 1 clause 3 has not been in effect.