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The interest on the Home Equity Line Of Credit may flow if the total loans on the property do not exceed the value of that property AND the funds were used to “buy, build or substantially improve the taxpayer’s home that secures the loan”.
Mortgage interest for the second home may also flow if the loan is secured by that second home. If you take a HELOC on one home to purchase a second home, that interest will not be tax deductible.
Finally, the amount of interest you can claim is limited to $500,000 (or $375,000 if filing Married Filing Separately) if the loan was secured after December 15, 2017. (There is an exception for sale contracts signed before December 15, 2017, but not closed until 2018).