Not quite sure what your question is here. You're jointly legally responsible for the debt owed if in fact you cosigned on that contract and if the primary party refuses or is unable to pay, the liability is yours, in my opinion. You in effect co-guaranteed payment, whether in monthly installments or in full and the creditor is well within their rights to pursue either (or both) parties. I'd hazard a guess that insurance was also required in that contract as well.

You've made no mention of the primary party, but assuming worst case scenario that you're now 100% responsible, you have 2 choices (again, in my opinion): 1. Honor your original agreement and approach the creditor with written terms of repayment. That may not prevent a chargeoff/judgement from appearing on your credit report but to most creditors, does represent a willingness to at least attempt to honor your obligation. If the creditor refuses and demands payment in full, you can either seek alternate (more manageable financing,) i.e. a secured loan, for example. 2. You can choose to ignore the demand for payment and not only face extremely derogatory credit for the next 7-10 years (depending on your jurisdiction), but face endless pursuit by the creditor resulting in not simply derogatory credit, but possibly wage garnishment/assignment, or liens against any real property you might own. Quite simply, the choices are yours to make.

Depending on the circumstances surrounding the accident, i.e. who was determined at fault, whether the other vehicle was insured, etc. you may be able to recoup some of your losses in separate action from your original question. Keyword: MAY. An attorney in your area can better evaluate that possibility, as well as advise legal pursuit of the primary party on the note/contract. Admittedly, this probably isn't what you wanted to hear, but the terms of that note you co-signed were most likely very specific. (Personally, I'd suggest consulting a good attorney in your area first.)

Hope these suggestions/opinions help a bit. Good luck.