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2020 Outback Limited
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Discussion Starter #1
Just retired my 2002 Subaru Outback LL Bean (250k miles) and for a couple of years prior have been towing a small utility trailer using a cheap Walmart trailer light system by Blazer with no problems. Plugged my trailer into my new Subaru...nothing. No lights. Checked voltage at plug connected to Subaru hitch (had installed post purchase), and have full voltage delivery. Just to confirm, plugged my old Subaru back in and have full lights. What is my issue?!!! See pic attached of plug from trailer plug. Thanks very much for feedback.
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2010 2.5 CVT Limited
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Probably not getting a good ground (return) path.
The standard 4 pin connector provides signals for running, brake, left and right. The ground is established through the tow ball.
The pic you posted is a 5 pin so your trailer may have isolated the ground from the frame. You may need to add a wire from the ground wire of the harness to the frame.

Edit: after writing the above, I reliazed I made a mistake in how the circuits are arranged.
The 4 wires are: running, left & right blinkers and ground. The left and right also activate the brake lights.
But the suggestion of checking grounds is still the first place I'd look.
Does your OB have a 5-pin connector too? Else how do you mate the two together without an adapter?
 

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2020 Outback Limited XT
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With problems with any 12 volt system, always check for a ground problem.
 

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Discussion Starter #5
Probably not getting a good ground (return) path.
The standard 4 pin connector provides signals for running, brake, left and right. The ground is established through the tow ball.
The pic you posted is a 5 pin so your trailer may have isolated the ground from the frame. You may need to add a wire from the ground wire of the harness to the frame.

Edit: after writing the above, I reliazed I made a mistake in how the circuits are arranged.
The 4 wires are: running, left & right blinkers and ground. The left and right also activate the brake lights.
But the suggestion of checking grounds is still the first place I'd look.
Does your OB have a 5-pin connector too? Else how do you mate the two together without an adapter?
Yeah, you see I have a good ground. Other picture shows plug on Subaru. They fit together (Subaru to Trailer harness). Also depicted is the wiring setup I have. One friend suggests that my subaru plug is on a different circuit than the trailer and I'd have to re-do the trailer plug so power aligns. Maybe I can get an adapter?

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trailer4.jpeg
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492698
 

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Other picture shows plug on Subaru.
Not sure which picture is the Subaru, and which is the trailer.

There is a photo of a 5-wire connector in post #1 above, and a picture of a 4 pin connector in post #5. Can you better identify where these connectors are located?

Are you connecting the 5-wire connector shown in post #1 to the 4-pin connector shown in post #5?
 

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2020 Outback Limited
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Discussion Starter #7
Yes, sorry to confuse. That is the case, as you state. 4-pin connector in post #5 is on the Subaru.
 

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If none of the lights are working then you should check your ground as was mentioned earlier. The ground is supplied through the white wire on the plug. If you have a voltmeter you can check the voltage to the wires supplying 12 volts to the trailer lights. The two brown wires next to the white (gnd) are your running lights, one on each side of the trailer. The yellow is the left brake/turn signal and the green is the right brake/turn signal. Make sure the white wire on the trailer side is going to the frame of the trailer.
 

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2020 Outback Limited
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Discussion Starter #12
So, repeating the question:
Are you connecting the 5-wire connector shown in post #1, which is on the trailer, to the 4-pin connector shown in post #5, which is on the Subaru?
Yes, that is the case..
Further, as I mentioned, I hooked the trailer up to old Subaru, and lights shined bright.. so, I think the ground is good -- unless i'm missing your point? thx.
 

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Discussion Starter #13
Yes, that is the case..
Further, as I mentioned, I hooked the trailer up to old Subaru, and lights shined bright.. so, I think the ground is good -- unless i'm missing your point? thx.
Also, double checked power through plug on Subaru... good DC power.
 

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Yes, that is the case..
Further, as I mentioned, I hooked the trailer up to old Subaru, and lights shined bright.. so, I think the ground is good -- unless i'm missing your point? thx.
I didn't think a 5 pin connector could fit properly on a 4-pin, and then even if it could, there's the question of whether the 4 circuits of the trailer are being connected to the correct 4-wires of the trailer. In the 4-pin connector, the single bare contact is the ground, and as noted above, is usually a white wire. So it looks as if the white wire on the trailer connector should be matched up with the bare contact on the Subaru connector.

But, the trailer wiring shown in post #5 shows only 4 wires, and yet it has a 5 wire connector. I'm really puzzled.
 

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I didn't think a 5 pin connector could fit properly on a 4-pin, and then even if it could, there's the question of whether the 4 circuits of the trailer are being connected to the correct 4-wires of the trailer. In the 4-pin connector, the single bare contact is the ground, and as noted above, is usually a white wire. So it looks as if the white wire on the trailer connector should be matched up with the bare contact on the Subaru connector.

But, the trailer wiring shown in post #5 shows only 4 wires, and yet it has a 5 wire connector. I'm really puzzled.
The connector with five wires only has 4 pins. The two brown wires are both connected to one pin.
 

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The connector with five wires only has 4 pins. The two brown wires are both connected to one pin.
Ah!. Right. I misunderstood that. Back on track . . .

So, if we match the white wire to the bare pin of the connector on the Subaru, then based on the 2002 with a trailer adapter:

the two brown wires would be tail/marker
the yellow would be left turn/brake
the green would be right turn/brake.

The four pins on the Subaru connector should follow that convention. Should be easy enough to check that the bare pin goes to ground, and that the other three have power when they should.

If the 2020 Subaru has a trailer adapter to convert from the 8-pin connector in the cargo area to the 4-pin connector in the photo, it requires a source of 12 V. I don't have a 2020 wiring diagram, but there's usually a fuse dedicated for this either in the engine area fuse box or in the cabin fuse panel. Perhaps it hasn't been installed. (In the 2019, it was fuse #28, 20 Amps, in the cabin fuse panel, but 2020 is a new generation and might not be the same.) Also, some adapters have their own fuse. Along with the ground, these should be checked.
 

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Discussion Starter #17
The connector with five wires only has 4 pins. The two brown wires are both connected to one pin.
Yeah, it's a Blazer product, can't find specific model, but the two wires going into one there are brown/yellow and brown/green. Think I may have posted wrong diagram from earlier install... :-(

As far as power from new Subaru, there is good power coming from that plug. And again, think ground is good on trailer since when I hook to old Subaru, lights fired right up. Do I need a BETTER ground?? thx.
 

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As far as power from new Subaru, there is good power coming from that plug.
The fact that the trailer lighting is fine with the 2002 does suggest the trailer wiring, including the ground, is not the problem.

How did you check the power at the 4-pin connector on the new Subaru? If the power there is correct, and, the trailer is plugged into the connector properly, there's no reason why the trailer lighting shouldn't work.

Here's what I would expect, when making measurements between each pin and a good ground, with a multimeter:
492864
 

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Discussion Starter #19
The fact that the trailer lighting is fine with the 2002 does suggest the trailer wiring, including the ground, is not the problem.

How did you check the power at the 4-pin connector on the new Subaru? If the power there is correct, and, the trailer is plugged into the connector properly, there's no reason why the trailer lighting shouldn't work.

Here's what I would expect, when making measurements between each pin and a good ground, with a multimeter:
View attachment 492864
 

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Discussion Starter #20
So, tested again with my voltmeter and getting full power to each and when blinkers on, fluctuation as you'd expect in 2nd/3rd pin. I've got it set for 20v on my meter and it goes up to ~14 but hovers at ~12/13. Zero resistance on Ohms... What the heck am I missing?!! And thanks very much for awesome illustration...
 
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