It's an earth fault. Always is.
What have you done thus far ? when did this start ?
Remake all the earth points you can find - tis good maintenance anyway - and make damn sure that the engine and gearbox earth straps are in good order .... AND that you handbrake cable isn't the only earth ....
A search on here should help you ... but you might ending tracing the circuit diags in RAVE to find the actual missing or extra earth.....