I have been doing a little electrical work on both of my TW’s and I thought I would put together a little how-to on wiring up a relay and some theory on what they are and how to use them in relation to our TW’s for those that are not familiar with how to wire up a relay.
What is a relay?
The simple answer is it’s an electronic switch. It operates similar to a manual switch but instead of using your finger to turn it off it uses an electronic trigger to turn on and off. A relay will also allow you to run a high current application with low current switch to turn it on and off. Some examples of where you would find relay. The headlight’s on your car, power trim on an outboard, the power button on your TV.
There are many types of relays but for the TW there are two that we will concentrate on. Single pole single throw(SPST) and single pole double throw(SPDT).
A SPST relay is an on/off switch. The output of the relay is on or off depending on the presence of voltage on the trigger input. There are 4 connection points on a SPST relay , they are standardized and numbered
#30 goes to +12v constant, the pos terminal on the battery is a good place.
#85 goes to ground
#86 goes to your trigger, switched power or a manual switch.
#87 goes to your accessory that you are connecting.
Here is a schematic picture of a SPST switch.
A SPDT relay is similar to a SPST relay with one difference. It has an extra connection (87A) that will have power when there is no voltage on the trigger port. So when the connection #86 has no power 87A will have +12v when the trigger has power 87 will have +12 and 87A will be off. There are 5 connection points on a SPST relay , they are standardized and numbered
#30 goes to +12v constant, the pos terminal on the battery is a good place.
#85 goes to ground
#86 goes to your trigger, switched power or a manual switch.
#87 goes to your accessory that you are connecting and will have power when the trigger has power.
#87A goes to another accessory that you are connecting and will have power when the trigger has no power.
Here is a schematic picture of a SPDT switch.
Now that we have seen what a relay is, where do we use these on our TW’s? I can think of a couple places. First would be to run an accessory and turn it on and off with the bike automatically. On my tw’s I have a phone charger that will flatten the battery but it’s a pain to get access to turn it off, this is a perfect application for a relay. Another place would be accessory lighting. I used a relay on my bikes to turn my aux lighting on when the high beams are selected and turn them off when the low beams are selected automatically. Both of these are accomplished with a SPST relay. The reason I mention a SPDT relay is it can be used as SPST relay, I will demonstrate this in my install that I documented.
On to the install.
As I mentioned I have a phone charger that will flatten a battery in a matter of a few days if I don’t turn it off. When I originally installed this charger it I put the charger itself behind the right side panel where the fuses are and the toolkit is located. Its kind of a pain to remove the cover every time I park the bike so I decided to do something about it and pop a relay in there to turn it on and off with the bike.
Step one was choosing a relay. A SPST relay is what I need for this application but I actually ended up getting a SPDT relay. Why? Availability of a waterproof one is the reason.
This a standard SPST relay, the only problem is it’s not waterproof and TW’s tend to get wet so it wont last. I have seen these fail in the past when moisture has been in the picture.
Here is the relay that I bought and its associated wiring harness. Its made by Hella and its waterproof with a nice gasket on the socket. It’s a SPDT relay but by simply not using the 87A wire it will function as a SPST relay. I got these from amazon, see the links below.
Link to Relay
Link to Harness
From here we have to identify what wire does what. I really wish Hella did a better job here on color coding the wires. Having 3 the same color is kind of dumb in my opinion and while they were nice enough to number them they are numbers incorrectly. The ground and trigger wire are self explanatory, the ground is black and trigger blue. They did put a schematic on the relay and I was able to determine what was what by that.
What I figured out is port# 3 = 30 and port#5 is 87 and 4 is 87A . Looking at the harness itself #87 is the wire closest to the locking tab that holds the relay in place, 87A is in the center and 30 is the wire on the outside.
Since we are using this is a SPST relay 87A is not needed. What I did was cut that wire off, fold it over and put shrinkwrap over it to prevent shorts. I also put some RTV silicone on the wire to seal it up before I put the shrinkwrap on. Here is what it looked like.
Next up is placement. I decided to put this right next to my phone charger, there is plenty of room for it there and it will make it easier to wire everything up.
Now I need to find a place to tap into for my trigger voltage. Looking at the schematic for the bike I found there is a brown wire that is turned on and off by the key. This brown wire is found many places on the bike. I found one in a perfect spot for my install right at the rear brake light switch.
I tested this wire with my meter to make sure it would go on and off with the key.
Key off, no voltage on this wire
Insert meter key on
Key on, and I get voltage.
Now that I have found a spot to get my trigger source I need to tap into it. There are a few ways to do it. I could cut the wire and connect to it that way, use a scotch lock connector or build a pigtail connector so I don’t have to cut anything. When I do stuff like this I hate to cut into the factory wire so I decided to make a pigtail and leave the factory wires unaltered.
I happen to own the tool that makes non insulated connections like the factory does and I have the 4mm bullet connectors with the weather insulators. I made a simple pigtail that will plug in and give me a lead to connect to my relay’s trigger point.
Here is a pic of it installed
Now its time to install and test the relay. As I mentioned earlier I decided to put this next to my phone charger, it fits perfect and I held it in with some double sided 3M tape. I also connected it up temporarily so I can test it. I hooked the #30 port to the battery pos, the black wire to the battery neg and the blue to the pigtail I made. I then hooked up my meter to the port 87 wire and tested it.
Here is the meter showing me a successful test when the bike is turned on.
Now its time to complete the wiring and tidy everything up. The two wires connected to the battery will ultimstely end up being connected to the battery. I had to extend the neg wire and put a run terminal on the end to connect to the battery. The pos side I connected a waterproof fuse holder to the wire for port #30 and connected the fuse holder to the battery. The port 87 wire is connected to the phone charger’s pos input.
I should also note that I uses shrinkrap connectors on all of the connections I made. They make corrosion much less of an issue.
Here is a shot of the completed install.
Phone charger with the key off. Note the green LED is off.
Phone charger with key on. Note the green LED is on showing that it has power.