I am 60 years old and on permanent disability I want to cash in my 401-k to pay down my mortgage how will this effect my disability and taxes?

You should start withdrawing it after age 59 1/2.
You pay taxes on what you withdraw.
Assuming your SS is SSDI and not SSI, then the withdrawals won't affect your SS.
If you have any state run (welfare) benefits such as Medicaid and food stamps, then it will affect those.
You shouldn't 'pay down your mortgage' just because you can. It depends on the interest rate, the balance of the loan, and what your total finances look like.
You need financial advice in person, going over all your numbers, and what's a good amount to withdraw. There's no exact formula or 'right' way, because we don't usually know our life expectancy and what our health will be like.

Joy is great advice. Heed it!