Author Topic: DIY Trailer Wiring Relay  (Read 1651 times)

Offline blerko

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DIY Trailer Wiring Relay
« on: November 13, 2015, 01:02:05 PM »
Thought I'd post my latest project for two reasons... Feedback to see what the community could add/change to improve my initial attempt, and to share one method to wire up a trailer outlet with little cost (under $50) for anyone considering it.

Got a 2002 ST1300 from one of the local dealers earlier this year which came with a towbar, but they had disconnected it and in the process sliced the trailer wiring to get it off. Probably a good thing in hindsight, because the wiring was just piggybacked to the tail lights which I'm led to believe is not the ideal way for the electrical system to cope.

Having read around, I've made my own relay, but I've got to warn you that some may find the following pictures disturbing. It's very messy. Spaghetti messy.

I found this thread on ST-Owners.com and figured the logic and method of making your own relay could possibly be done by a novice like me. BTW - I've uploaded the images from that thread to an image hosting service rather than leech off the ST Owners server. If that's not the preferred way, let me know and I'll post the links to the original images.

The two images in that thread I've used for my wiring are...

The relay wiring:


And the connections to the ST1300 wiring:

I've decided not to fuse earth as shown in the second image because I've never seen it on any car radio I've wired before. If anyone thinks this should be fused, let me know.

So... I've headed out to Jaycar with a basic shopping list and come back with
*  7-core trailer wire
3 fused relays
*  12v red and black wire
project box
12 pin auto socket
*  various female spade connectors
*  a mini-fuse piggyback
*  some plastic wiring splices

In hindsight, the 12v red and black wiring was a way heavier gauge than I needed, and created some problems when trying to connect everything together.

The fused relays (SPST) got my attention by having the fuse I required already built in...


Ok, so this is where the spaghetti "mess"-tern begins. I've decided red wire for power, black for earth (naturally) and following the diagrams - yellow/right, brown/left, blue/brakes, green/tail. As per the diagram, left, right and brake will have a relay while the tail light will be powered directly to the 12v supply. By following the wiring in the first image, it's possible to solder and/or crimp the left/right/brake relays together with the power (pin 30) and earth (pin 86) wired in series. I then connected pins 85 with a single wire to go to the 12 pin connector and used a red permanent marker to distinguish them from the wires to pin 87.

Brace yourself... heres what it looks like in the project box.


And here's the wiring from the base of the relays:


Ok, now it can be hooked up  to the 12 pin connector:

You can see in the photo that I've bridged the incoming 12v out across 2 pins to supply the relays and to power the tail light directly (earth similarly bridged across 2 pins). If anyone's interested in how I wired each side of the 12-way connector, l can post it.

Now that's complete we can hide the mess by closing the lid - once you've written the pin connections inside the box for future reference/troubleshooting, of course!


So, we can now hook up the box to the bike. The second image in this post has the wiring colour codes in the tail for sending the "signals" to the relays.

For power, I've tried a piggyback fuse connector. This one keeps the "donor" fuse doing it's original job...


Wiring in the fuse is as follows:


So now the box fits neatly in the tail, easily accessed if there's a blown fuse:


Some questions for those with more knowledge than me:
Should I replace the 15amp fuses in the relays with smaller fuses? As described above, is a fuse on the ground wire recommended or to be avoided?

Feedback/praise/ridicule/questions/OH&S advice all welcomed!  :thumb
 

Offline Gadget

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Re: DIY Trailer Wiring Relay
« Reply #1 on: November 13, 2015, 01:21:21 PM »
My only concern is the 2nd last picture has a 20 amp and 30 amp fuses on cable only designed for 30 amps. That is a lot of potential overload.

I would prefer a 30 amp feed durect from the battery controlled from say 5 amp relay fed from the ignition power.
Cheers,
Gary
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Offline blerko

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Re: DIY Trailer Wiring Relay
« Reply #2 on: November 13, 2015, 01:30:21 PM »
My only concern is the 2nd last picture has a 20 amp and 30 amp fuses on cable only designed for 30 amps. That is a lot of potential overload.

I would prefer a 30 amp feed durect from the battery controlled from say 5 amp relay fed from the ignition power.

Thanks, Gary. That's the max load you can put on the adaptor. I should have described how I used it: The adaptor goes in an existing fuse socket and the original fuse goes in socket 1 (in my case a 10amp fuse), keeping it separate from fuse 2. In socket 2 I have put a 15amp fuse to match the relays, but I'm wondering if I replace all the fuses on the adaptor and relays with, say, 5amps in case of inadequate overload protection as you point out?
 

Online alans1100

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Re: DIY Trailer Wiring Relay
« Reply #3 on: November 13, 2015, 01:49:55 PM »
It certainly is a different way of doing it. My trailer plug is wired from the tail lights and done by friend who does similar in their model railway. So all wires soldered, shrink wrapped and electrical tape over that. No issues in over nine years with two trailers in that time. Current trailer has the lights (except interior) converted to LED as they're supposed to last longer than globes.
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Offline blerko

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Re: DIY Trailer Wiring Relay
« Reply #4 on: November 13, 2015, 02:35:05 PM »
LED's would certainly reduce any potential strain on a system, too. I actually haven't got a trailer (yet), so I was pre-emptively concerned about the changes running extra globes would have. Probably based on how a car's indicators will change speed based on load (i.e. blown globe). In that case I probably have overdone it if directly tapping the wiring works ok (which is how the previous owner had done it on mine), but I suppose I can look at it as the afternoon's equivalent of doing a jigsaw - personally satisfying but an unnecessarily complex way to get the whole picture  :whistle
 

Offline Gadget

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Re: DIY Trailer Wiring Relay
« Reply #5 on: November 13, 2015, 03:51:27 PM »
Yes. LEDs certainly make parralleling up easier.

My concern for the splitter was the feed wire to the original fuse.
Cheers,
Gary
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Online alans1100

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Re: DIY Trailer Wiring Relay
« Reply #6 on: November 13, 2015, 04:06:43 PM »
With the trailer needing only five of the flat seven pin connections I didn't see the need to have the extra two connected into the bike. Those two would have been for caravan interior lighting and maybe electric brakes or 12 volt power to the fridge. That was ok on my first trailer but the one I have now is wired for the interior light so to get that working I moved the wire over to the taillight feed. Just means if I need to see in the trailer at night while on the road I have to leave the lights/motor on.
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Online Brock

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Re: DIY Trailer Wiring Relay
« Reply #7 on: November 13, 2015, 04:41:00 PM »
There is a lot of noise on the US site, about isolating the trailer from the bikes lights. I dont really see the need, as the additional load isnt high. Trailer bulbs are usually only a few watts, and you need to be consuming 12 watts to draw 1 amp. There isnt any difference in wiring up the top box to brake and indicator lights.

That apart, you seem to overdoing the fuses, as you only need a fuse near the source, in the supply line. The fuse in the return is not needed, as nothing you do will cause it to blow unless you hook up some driving lights . If you short the return to ground, the current will just go to ground.

To protect your isolated system, you only need a 5 amp fuse on the supply line, 3 amps (if there is one) would be fine. With both indicators on and the brake tail light, you would be lucky to draw 5 amps.

I dont like pigy backing off fuses, its like using double adapters, run a separate line through a switched supply circuit.
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