Can you write off interest on a line of credit? Not a home equity loan

No.  According to the IRS, interest on home equity loans and lines of credit are deductible only if the borrowed funds are used to buy, build, or substantially improve the taxpayer's home that secures the loan.

A personal line of credit?  No.

A Home Equity Line of Credit?  Only if the funds were used to make improvements to your personal residence.