first post here. I'm wiring a DC motor and horn that will go into a small boat I built. I would like to get some help to see if I'm doing this correctly.

-DC motor hooked to a 12v battery (Max draw 30 amps, manual calls for 50a breaker) -A foot pedal momentary switch turns the motor on. -A 3 position toggle switch controls if the motor will go clockwise (forward), counterclockwise (reverse), or off. -There is also a momentary button to power a horn.

I've built it and it works but I want to double check that there are no problems here and that its safe. Since the motor draws a lot of amps above the rating of the switches I'm using 2 relays.

Attached are pictures of how it's wired and also a picture of it wired up.




  • \$\begingroup\$ You should use larger wire - at least #10 - for all the high-current leads: battery to fuse to relay contacts, and relay contacts to motor (and motor back to battery).. \$\endgroup\$ – Peter Bennett Jun 19 '16 at 16:14
  • \$\begingroup\$ I am using #10 wire everywhere I can, but the leads coming from the relay seem to be smaller, maybe #12, but it's rated at 50amps so that confuses me. Should I get relays with larger wire leads? \$\endgroup\$ – HkySk8r187 Jun 19 '16 at 16:24
  • \$\begingroup\$ I also recommend reading up on the subject of "ampere capacity" (a.k.a., ampacity) of wire. Note that wire has resistance; so the longer a wire is, the greater the voltage drop will be for a given current flowing through it (and the greater the temperature rise due to power dissipation, etc.). Search the Interwebs using the keywords "awg ampacity". For example, here's a site that provides some handy ampacity graphs for marine applications: westmarine.com/WestAdvisor/Marine-Wire-Size-And-Ampacity \$\endgroup\$ – Jim Fischer Jun 19 '16 at 22:21

You have the relay contact connections shown wrong in the diagram. Since it works, it must be wired right. In the switch position shown, both motor terminals are connected to negative. In the opposite position, both terminals are connected to positive. The motor fuse should be a slow blowing type to accommodate the motor starting current.

The relay coil wires can be small, but the contacts need to be #10 at least. Be sure the relays are DC rated and motor rated.

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  • \$\begingroup\$ I'm not following... only one relay would activate at a time, making the motor have one positive and one negative. Am I missing something? \$\endgroup\$ – HkySk8r187 Jun 20 '16 at 5:47
  • \$\begingroup\$ Your diagram is correct. I was thinking of the scheme in which one relay with two sets of contacts is used. \$\endgroup\$ – Charles Cowie Jun 20 '16 at 11:06

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