It’s not the inquiries you need to worry about but the payment to income ratio that co-signing may create. When you co-sign the monthly payment for the loan you co-signed is added to your total monthly payment obligation because you may have to begin making those payments anytime and without further input to the credit reporting system.

So co-signing could make you ineligible for much further credit because of the resulting change in your payments to income ratio, no matter what your payment history is.