Having bad credit will almost always disqualify you for a home equity loan even if you have a current mortgage through the bank you apply for the home equity loan.
To qualify for and be approved for a home equity loan your credit score needs to be a minimum of 600 or above.
The higher the credit score the more likely you're to be approved for a home equity loan but unless your credit score is at least 600 then you're unlikely to get approved for the home equity loan.