does this look correct? power for relay
Printed From: the12volt.com
Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=129410
Printed Date: September 17, 2025 at 8:35 AM
Topic: does this look correct? power for relay
Posted By: rdman
Subject: does this look correct? power for relay
Date Posted: November 27, 2011 at 4:59 PM
I am adding a fuse panel to my motorcycle to power up some accessories. I understand relays a bit from reading on the web. I already have a relay and fuse box wired into my bike and no switch to my driving lights. I now want to add a switch so I can turn the lights off. I guess my question is, is it acceptable to get the main power for the relay from the fuse panel or should I tap in the the main wire from the battery?
Replies:
Posted By: rdman
Date Posted: November 27, 2011 at 5:04 PM
Diagram that I have drawn up
Posted By: howie ll
Date Posted: November 27, 2011 at 5:23 PM
Your layout is quite correct.
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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: rdman
Date Posted: November 27, 2011 at 6:06 PM
Thanks for the confirmation. One more question, how big should the relay be that feeds the power to my fuse panel? Should it be more than what amps are being pulled off of the fuse panel? Right now I think I have a 30 amp relay.
Posted By: howie ll
Date Posted: November 27, 2011 at 6:26 PM
You've got me thinking now!
Keep the layout as it is with a 40 amp fuse OR a safer layout:-
power_distribution.bmp------------- Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: rdman
Date Posted: November 27, 2011 at 6:33 PM
I don't understand your diagram. This automotive wiring and relay thing is a new thing for me! Should my fuse running to my relay be of the same size as the relay or should it be bigger? If the relay is a 30 amp, then the fuse off the battery should be 40?
Posted By: howie ll
Date Posted: November 27, 2011 at 6:41 PM
Yes.
In fact since you have 2 relays and the consumer end, driving lights, 2 front and one rear = 30watts = 2.5 amps, add on rush (the surge when you turn on a reactive load) about 7.5 amps.
The headlight on high will draw 55 watts, less than 5 amps so your draw there say 10 amps.
Add 15 amps for the outlet
Total draw including relay coils about 35 amps,use a 40amp fuse and layout, it's quite adequate fro that circuit.
Normal rule is add 1 amp per metre of wire to the fuse rating.
e.g. an amp in the rear rated with a 20 amp on board fuse should have a 25amp fuse at the battery end.
-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
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