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HOW TO: Wiring new accessories through a RELAY

112K views 231 replies 81 participants last post by  eagle 
#1 ·
I came across quite a few fellas who were unsure how to wire new accessories on their bike. Those who are totally unfamiliar with electricity will be interested to know that if you add too much ballast (wattage-drawing devices) to your AUX plug in the headlight bucket, you are likely to draw more than 10 Amps, for which it is fused. The fuse rating is matched to the 18 AWG wire used by Suzuki, so the fuse protects the WIRE first (from overheating) and your devices second. Since we can't change the OEM wire from Suzuki running through the harnesses, we have to live with what they gave us: A 10 Amp circuit translating to a maximum of 120 Watts ballast.

Even if the fuse withholds higher Amps (and it usually will, which is quite contradictory to their purpose), your wires, now getting pretty warm in the IGNITION SWITCH, will slowly but surely damage the switch which may eventually fail. So you want to put add'l accessories on their own circuit with a relay.

A relay is an electric switch which, when energized, will close a second, totally independent circuit. Below is a drawing I made for a simple setup of wiring two add'l driving lights. Note that the rocker switch gets its energy from the IGNITION circuit and when turned on, will close an independent circuit (in the relay between poles 87 and 30) and safely run your lights (or anything you connect) on it's own, fused(!) circuit.

Why do we want a relay and not simply wire the lights directly to the battery? Well, of course you can do that, but if you do, the lights will come on whenever someone throws the switch, even if no key is in the ignition. Or, you walk away from the bike accidentally leaving your lights on. 3 hours before your battery is dead! A correctly wired relay will only allow the circuit to your aux. lights come on when the ignition is on.

Just for clarification on the drawing: This drawing assumes that you have a LIT switch where a little light comes on when it's in the "on" position. That is the only reason there is a third post on the green rocker switch - to energize the lit button. If you have just a simple, unlit toggle switch, it will only have two terminals, so you can forget the third one with the black ground wire coming from it (in my drawing I spliced it to negative in the circuit).

Also you will wonder why I just said that the AUX can handle 120 Watts but my lights in the drawing only add up to 110 Watts. You are correct, just that 120 Watts is the MAXIMUM load the wires can safely handle, but not continuously. So we're getting pretty darn close to their acceptable Ampacity, making it safer to go this route.

The wires coming TO the Aux plug in the headlight are orange with blue stripes (positive) and black with white stripes (negative).

There are wiring harnesses on the market that have this cicuit so you don't have to wire yourself if that's not your cup of tea, but they still usually need a little modification here and there. Check at autozone.com, Part# PL-HARN3

I used a 20 Amp fuse in my drawing, which is actually overkill for the driving lights. 15 Amps would do fine, even 10 in a pinch. Just make sure to match the fuse to the WIRE SIZE that it protects (see charts posted belows).

Hope this helps. Any questions, just PM me.

 
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#4 ·
Jay, you're welcome. I just REVISED the drawing as follows:

1) Rocker switch: had a wrong diagram shown. The only reason the switch has a black (ground) wire is because it is a LIT switch. A simple unlit pole switch would not have a contact for ground

2) I routed the black (negative) from the lamps DIRECTLY to the NEG battery terminal, so it is clear that this is not mechanical ground, but must go back to battery.

ALSO REMEMBER: The battery is usually showing 13.1 or so Volts on your voltage meter ... that is the IDLE voltage. Once you draw from it, it will be in the 12 Volt range, so in your AMP calculations, always divide by 12, NOT 13 !!!
 
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#6 ·
Ok, here we go. I got everything taken apart (now that the sun is setting) and my wiring doesn't match your picture. Somehow, it seems as though the positive wires from both spotlights and the switch are all sliced together into one wire. The same with the negative wires. There is one red wire and one black wire plugged into the light accessory connection in the headlight bucket. Do I have to separate all these wires in order to connect them correctly to the relay?
My lightbar is the OEM one and the local dealer installed it. AAARRRRGGGGGHHHHHH!!!!!!!!!!!!!!!!!!!!!!!!!!
 
#7 ·
Air4ceOne said:
Ok, here we go. I got everything taken apart (now that the sun is setting) and my wiring doesn't match your picture. Somehow, it seems as though the positive wires from both spotlights and the switch are all sliced together into one wire. The same with the negative wires. There is one red wire and one black wire plugged into the light accessory connection in the headlight bucket. Do I have to separate all these wires in order to connect them correctly to the relay?
My lightbar is the OEM one and the local dealer installed it. AAARRRRGGGGGHHHHHH!!!!!!!!!!!!!!!!!!!!!!!!!!
LOL, oh John, very hard to diagnose without pics or actually seeing the setup. The pos (RED) wires from the lights would naturally be spliced together (that splice would be at the wire coming from terminal 87 - see how it goes to both lights ... that intersection is a splice.

All negatives can be spliced together because they all go to mechanical ground, EXCEPT the ones from the spotlights - those should go back to the battery somehow.

It is VERY hard to follow the wiring if someone else did it because you never know where their connections lead to. Do you have a wiring diagram for your bike?

Carsten
 
#8 ·
I have the OEM and wired mine alittle different than the diagram shows. My switch is after the relay on the bar. My relay is in the bucket and controled by the headlight feeds. I wanted mine that way so the lightbar is off when headlight is off (ex. when starting bike less load).

Air4ceOne said:
Ok, here we go. I got everything taken apart (now that the sun is setting) and my wiring doesn't match your picture. Somehow, it seems as though the positive wires from both spotlights and the switch are all sliced together into one wire. The same with the negative wires. There is one red wire and one black wire plugged into the light accessory connection in the headlight bucket. Do I have to separate all these wires in order to connect them correctly to the relay?
My lightbar is the OEM one and the local dealer installed it. AAARRRRGGGGGHHHHHH!!!!!!!!!!!!!!!!!!!!!!!!!!
 
#9 ·
C50T2006 said:
I have the OEM and wired mine alittle different than the diagram shows. My switch is after the relay on the bar. My relay is in the bucket and controled by the headlight feeds. I wanted mine that way so the lightbar is off when headlight is off (ex. when starting bike less load).
There is no one single correct setup, of course the switch can be before the relay or after, doesn't matter at what the circuit is interruped. I will wire mine the way you did, Dane, relay in the headlight bucket, switch on top of the head light. The lights won't come on unless I flip the switch. If you want your lights to come on when the bike starts, of course a switch isn't needed. Again, I tried to make a simple diagram how it CAN be wired and will correctly work. Those who know as much as you can, of course, alter to their needs ;)
 
#10 ·
Well that didn't help me. I'm still totally confused! :? :( :lol:
I was actually hoping that the two positives from the lights would be spliced together, but I wasn't expecting them to be spliced into the positive from the light switch too (as well as the negatives). I'm guessing I'm gonna have to do some wire cutting and rewire things, which I REALLY HATE to do.
 
#11 ·
Air4ceOne said:
Well that didn't help me. I'm still totally confused! :? :( :lol:
I was actually hoping that the two positives from the lights would be spliced together, but I wasn't expecting them to be spliced into the positive from the light switch too (as well as the negatives). I'm guessing I'm gonna have to do some wire cutting and rewire things, which I REALLY HATE to do.
John, just sent you a PM. I think you should drive down to see Dane and have him check it out for you - would probably be a nice ride anyway :)
 
#12 ·
Don't give up. A relay isn't necessary. Main concern is a separate fused power feed to the lights so not to over task the ign switch. Stock OEM lightbar uses the connector in headlight bucket for ground and positive 12V to switch. Replace those wires with fused power from battery and a better ground. With this setup you would need to turn lightbar on and off as having no relay you are wired directly to battery. There you are done. You can add a relay if desired. Relay is mainly needed for controlling higher amperage and/or voltage with lower amperage and/or devices. An example is the horn. The stock horn button wouldn't last long controlling a high amp horn like a stebel. Also, it allows switching on with bikes power. Making it more convenient to use.

Air4ceOne said:
Well that didn't help me. I'm still totally confused! :? :( :lol:
 
#13 ·
C50T2006 said:
Don't give up. A relay isn't necessary. Main concern is a separate fused power feed to the lights so not to over task the ign switch. Stock OEM lightbar uses the connector in headlight bucket for ground and positive 12V to switch. Replace those wires with fused power from battery and a better ground. With this setup you would need to turn lightbar on and off as having no relay you are wired directly to battery. There you are done. You can add a relay if desired. Relay is mainly needed for controlling higher amperage and/or voltage with lower amperage and/or devices. An example is the horn. The stock horn button wouldn't last long controlling a high amp horn like a stebel. Also, it allows switching on with bikes power. Making it more convenient to use.

Air4ceOne said:
Well that didn't help me. I'm still totally confused! :? :( :lol:
Dane, if he doesn't use a relay and wires his lights directly to the battery on their own circuit, anyone who walks by can flip the switch and the lights come on without needing an ignition key. Or, you forget the lights when you leave the bike because they don't turn off when the ignition goes off. I think a relay goes way beyond "convenience", wouldn't you agree?
 
#14 ·
DONE!!!!! Unfortunately, I wasn't able to get it working with the relay, so instead of breaking things and making it worse, I just wired directly to the battery. Works like a charm. Hopefully I remember to shut them off every time. Oh well, I guess a dead battery is better than a burned out ignition switch! Big thanks to everyone who's posted about this stuff for those of us who don't know what we're doing, and especially to Carsten who talked me through it on the phone last night!!
 
#15 ·
Air4ceOne said:
DONE!!!!! Unfortunately, I wasn't able to get it working with the relay, so instead of breaking things and making it worse, I just wired directly to the battery. Works like a charm. Hopefully I remember to shut them off every time. Oh well, I guess a dead battery is better than a burned out ignition switch! Big thanks to everyone who's posted about this stuff for those of us who don't know what we're doing, and especially to Carsten who talked me through it on the phone last night!!
John, well sorry to hear the relay didn't work out, but I'm glad you got the lights to work anyway. I asked BIKERPOP to PM you about the Mid-Atlantic Rally so if you attend, you can ask people there to check into the relay again if you wish - still find it the safest way. I just ordered a special relay (DPST Relay with yet another contact to switch TWO circuits at once, one for the lights and one for the cigarette lighter) but let's not get into that LOL. Was very nice talking to you last night, John.

Cheers,
Carsten
 
#16 ·
Actually that is a very good drawing of how to connect the wiring for your lights so that you don't burn out your ignition.

I added a 4 pt distribution fuse box to mine so that I could run more things off of the battery power but wanted to make sure that everything turned off when I shut it down.

It works great. I have my heated grips, aux lights, and 12V outlet off of this. It works the same way as your fuse box for all the other wiring.
 
#17 ·
summergirl said:
Actually that is a very good drawing of how to connect the wiring for your lights so that you don't burn out your ignition.

I added a 4 pt distribution fuse box to mine so that I could run more things off of the battery power but wanted to make sure that everything turned off when I shut it down.

It works great. I have my heated grips, aux lights, and 12V outlet off of this. It works the same way as your fuse box for all the other wiring.
Where'd you get the other fuse box, and where'd you install it?
 
#18 ·
summergirl said:
Actually that is a very good drawing of how to connect the wiring for your lights so that you don't burn out your ignition.

I added a 4 pt distribution fuse box to mine so that I could run more things off of the battery power but wanted to make sure that everything turned off when I shut it down.

It works great. I have my heated grips, aux lights, and 12V outlet off of this. It works the same way as your fuse box for all the other wiring.
That is actually a great idea if you plan to add more than one or two add'l accessories. Let me guess, the second fuse box is regulated through a relay that's switched by the ignition to give power to that second fuse box, correct?
 
#19 ·
moenko said:
That is actually a great idea if you plan to add more than one or two add'l accessories. Let me guess, the second fuse box is regulated through a relay that's switched by the ignition to give power to that second fuse box, correct?
Ok, nevermind. I'll never even attempt that! LOL.
BTW Carsten, I like your signature block! We actually have this hanging on our kitchen wall. LOL. And believe me, there's A LOT of sour Kraut in our house! :lol:
 
#20 ·
Air4ceOne said:
moenko said:
That is actually a great idea if you plan to add more than one or two add'l accessories. Let me guess, the second fuse box is regulated through a relay that's switched by the ignition to give power to that second fuse box, correct?
Ok, nevermind. I'll never even attempt that! LOL.
BTW Carsten, I like your signature block! We actually have this hanging on our kitchen wall. LOL. And believe me, there's A LOT of sour Kraut in our house! :lol:
Haha, John, like I told you yesterday on the phone, I made 2 lbs of Sauerkraut with Kielbasa and mashed potatoes last night for work ... my colleagues stay FAR away for me for some reason :roll:
 
#23 ·
moenko said:
A relay is an electric switch which, when energized, will close a second, totally independent circuit. Below is a drawing I made for a simple setup of wiring two add'l driving lights. Note that the rocker switch gets its energy from the IGNITION circuit and when turned on, will close an independent circuit (in the relay between poles 87 and 30) and safely run your lights (or anything you connect) on it's own, fused(!) circuit.

ok, so why is there power from the battery and the ignition? into the relay?

if you swicth the switch off, you would still have power from the battery?
would you not?
 
#26 ·
Hehe, don't know about "smart" but it it's ingenious nonetheless. m@c, I wish I could show you an open relay I have here at home, you would laugh at how simple of a device it is. When you send power to it from the options connector (between 85 and 86), you energize a small coil that acts as a magnet. Once the coil is energized, it "pulls" a contact down until it meets another contact and thereby closing a new circuit (between 30 and 87) straight from the battery. This new circuit can handle as much Amperage as the relay is rated for (usually 30 Amps in our applications). Depending on the wire size you use, make sure to match the in-line fuse to that wire (chart is on previous page).

Imagine that: You ask only around 3 Watts from the options connector to energize a magnet, and it will close a circuit of up to 30 Amperes (!!) for you; yet your ignition switch would never know, it's only being "tickled" by a barely noticable "ballast" of 3 Watts.

There are several styles and varieties of relays, you only need the most basic one, a so-called SPST (single pole single throw) relay with 4 posts, cost is about $5 in any auto parts store. A cheap peace of mind!

OH - lastly, if you plan on having the lights on ALL THE TIME whenever the bike is running, you can cut out the manual switch altogether. The relay will always be powered and so will your lights when you turn your key. What I don't like about that setup is that when you start your bike, you need a good amount of Amps from the battery to turn the starter - the add'l lights will take up to 10 Amps from the battery before you crank it, making this setup unattractive to me, but it will work.
 
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