My general contractor submitted a bill for electrical for $6000- Four months after the end of the project

Depends on the terms of your contract, the nature of the project (residential or commercial), and the actual value of the electrical provided - among other things. Submission of a bill four months late in of itself, is unlikely to excuse your duty to pay. But if the contractor previously represented that you had paid in full you would have a better argument. And other contractual as well as statutory issues may alter your obligations.