Help! Electrickery expert required

Wiring in my boot popper and I was wanting to use the handbrake switch to earth the popper switch. So far so good except I seem to be getting a parallel earth through the h/brake switch meaning the popper switch will be activate-able at all times, whether the handbrake is on or not. I'm guessing the handbrake switch is probably earthing back through the dash when voltage is applied from the popper switch.



To overcome this I'm thinking a diode added between the popper switch & the handbrake switch is required? If so, what specification of diode should I be looking at? The circuit has a 15 amp fuse fitted. I know nothing about working out what rating of diode I'd need other than 12v.



Thanks

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