Relay wiring question - Stromtrooper Forum : Suzuki V-Strom Motorcycle Forums
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post #1 of 4 Old 07-15-2016, 07:40 PM Thread Starter
Join Date: Oct 2013
Location: Toronto, ON
Posts: 43
Relay wiring question

To the electrically-savvy among you, a question.

I'll try to paint a picture...
- 12V USB charger attaches directly to battery, has its own in-line fuse
- PWD Stebel Nautilus horn wiring harness includes a switched relay (only powered when bike is running), also has its own in-line 30A fuse

I'm wondering if I can use the relay to switch both, in this order:

Battery > relay > (splice) USB charger & fuse > Stebel fuse to horn > horn switch

...Would this work?

I don't want to inadvertently short the horn or USB charger, and of course I wouldn't want to compromise the horn in any way. To me it seems like the USB charger would add very minimal additional draw to the horn circuit.

Ideally I would like to buy the Eastern Beaver heated grip connector, but frankly I didn't plan ahead enough for my upcoming trip. Maybe this will work just as well?

Any help appreciated!
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post #2 of 4 Old 07-16-2016, 03:51 PM
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I'm not familiar with your horn but you should have switched power at a number of points on your horn system, into the relay, out on one of the relay terminals and at the horn, you need to get a volt meter and test for 12v power with the ignition turned on.

One test lead on the positive terminal of the horn or relay and the other on the negative terminal of the battery, ensure the power drops off when the ignition is turned off.

Most horns have push on terminals and are a great place to get switched power as you can just use a piggyback terminal so you don't need to splice into any wires, as it is for a USB the loads can only be small so it will be OK, depending on the terminals used you could use the switched wires at the relay ?

You will still need to find a negative power source for the USB, that could be at the relay or at the battery.

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post #3 of 4 Old 07-17-2016, 06:21 PM Thread Starter
Join Date: Oct 2013
Location: Toronto, ON
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Thanks Rolex - I had a feeling the phrase "test with a voltmeter" would come up. Time to get one apparently.

I'm curious about your piggybacked connector idea - I'll be on the lookout for some male+female spade connectors.
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post #4 of 4 Old 07-19-2016, 07:07 PM
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You need two relays. Unless you just want the horn blaring all the time.

Leave the battery tender stuff hooked up.

Relay #1 switches on when the ignition is on, and feeds power to your USB stuff and the horn relay.

Relay #2 is activated by your horn switch and activates your horn. The purpose of the horn relay is simply to take the heavy load of the louder horn off your bike's horn switch. (Press horn switch, relay goes "click", horn goes "PARP".)

You could, of course, just hook up the second relay separately, but that means another set of wires. With the horn relay after the other relay, you only need one set of wires from the battery up to the front of the bike.

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Last edited by bwringer; 07-19-2016 at 07:10 PM.
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