Hey Joop:
Here's a photo (not mine); See Post #45:
https://www.fordbarn.com/forum/showt...ery+disconnect
When I bought my '29 coupe, the battery disconnect switch was under the hood and hooked to the negative battery post. To make it more convenient I moved the switch to the seat riser as you've indicated you want to do, and is shown in the photo. I also hooked it to the positive ground side of the battery to ensure everything is dead when the switch is off.
I've been real happy with that arrangement.
Mike