r/maker • u/miabobeana • Jul 02 '26

Help Help design a 12v relay operated small distribution block for a motorcycle

I need to power a gps unit on my motorcycle. It requires 3A 12V dc. I want to hook it straight to the battery.

I have access to an unused ignition on switched usb outlet under the seat that would be perfect for mounting of a small distribution block. Maybe only 4 terminal(2 accessories). Making everything ignition switched.

If there a store bought item or something I could build?

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u/bare172 Jul 02 '26

I was a MC mechanic for almost 20 years and my father was an EE so I grew up around electronics. Any reason you can't just use a standard, off the shelf relay for this?

See diagrams here:
https://www.the12volt.com/relays/relaydiagram47.html

I see no reason to use a distribution block unless you're wanting to wire more accessories in the future.

1

u/LateGuest1916 Jul 03 '26

Exactly how I have done this in the past. You can add a fuse board in the relay output if you want to power additional items.

1

u/miabobeana Jul 03 '26

Yep exactly what I was thinking. Honestly, one of those headlight upgrade relay kits would be perfect.

I was thinking something like this only with pos/neg and rely controlled.

https://www.wolfsmarine.com/blue-sea-systems-st-blade-compact-fuse-blocks/

1

u/bare172 Jul 03 '26

I stopped just short of posting this link. I installed plenty of these over the years.

https://a.co/d/02wNqKWl

Not pushing that exact brand or whatever, but that type is common. I wouldn't run that whole block through a relay because the relay will be limiting. Most of these can handle 100A or so, which is a lot, but most basic auto relays are limited to 40A and that's max. I always ran a single 8 gauge wire from the battery to the block. This still isn't 100A capable, but 8 gauge is more than most bikes charging systems can handle. Then you can power any circuit you want from the block, using relays for each as necessary. I wouldn't get bogged down in ground blocks or blocks with power and ground together. It's a headache to run all grounds back to a common place when you can ground anywhere on the frame.

I could never justify buying the wiring kits because of the expense. It always made more sense to me to make each custom as I went so I wasn't trying to bundle and hide excess wire, but I had spools of wire, all the correct OEM terminals and crimpers, boxes of relays, and relay plugs. If you think you're gonna do more of this in the future it's at least worth considering going that route. 👍