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Old 01-25-2021, 07:10 PM   #1
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Testing the Tow Harness

I'm troubleshooting a non-working tow-harness problem. The RV's running, turn and brake signals are not activating the lights on the tow car.

The cable between the RV and the tow-car, a Honda CRV, is good.

The RV is sending 12v at the pins like is should (turn, brake, running).

So the problem is on the tow end of things. The first thing I turned up was a very loose/dirty ground wire for the Hopkins tow harness on the Honda. There's no way that connection was any good. I've got that cleaned up and tightened down.

But I can't test the whole setup because my RV and my car are in two different placed right now.

Can I just use a 12 volt source to test the harness on my Honda? Is it safe for the Honda? I have an old Radio Shack 12v regulated supply I can use.

It seems to me that there isn't any chance that I could harm the Honda's electrical system (especially with the harness's diodes there to protect) AND if I disconnect the Honda's battery ground. That seems safe to me.

Is my reasoning okay or am I missing something? I'd hate to fry something because I was careless.

!!!THANKS!!!
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Old 01-25-2021, 08:47 PM   #2
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That's how a shop would test it. So go for it.

I'll add a drawing that may be helpful...your Honda may differ:



I'll go ahead and add a link to my ad free blog. Has a bunch of drawings of hardware like 7-blade and 6-pin toad connectors.

Towing stuff...
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Old 01-25-2021, 10:10 PM   #3
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Quote:
Originally Posted by Jim_HiTek View Post
That's how a shop would test it. So go for it.
Thanks for the diagram! Will be printing this out and keeping it in the "car bible."
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Old 01-25-2021, 10:13 PM   #4
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Did it used to work OK?
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Old 01-26-2021, 09:31 AM   #5
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Yes, a 12v power supply or a spare battery would work fine. Connect the ground to the towed car and then (carefully) place power to the 3 "key" pins one at a time to test parking lights, right stop/turn, left stop/turn.

You can do this right at the connector on the car and if all of that works well, you can connect the umbilical cord to the connector on the car and apply to the 12v to the pins at the MH side of the umbilical cord. This will allow you to test the umbilical cord and allow you also to verify the "pin mapping".
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Old 01-26-2021, 12:01 PM   #6
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What got me looking in to this in the first place was, obviously, my toads brake/turn/run lights not working while plugged in. Further investigation revealed a blown "running light" fuse on my RV's towing box. That raised a flag, for sure.

Well, I've tested the harness by applying 12 volts directly to each wire: brown (running) and green/yellow (stop/turn l/r) and nothing lights up. The ground wire is good.

So if the running light fuse on my RV has blown and the harness seems to be non-functional it is maybe safe to say that there is a short somewhere. It seems odd that literally none of the wires seem to be carrying 12v to any of the lights even if I bypass all of the connectors and apply power directly to the bare harness wires.
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Old 01-26-2021, 12:05 PM   #7
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Did it used to work OK?
That's actually a good question! Yes, it did work. We've been parked a while and I have to admit once it was installed and working I didn't check it all that often so i can't be sure when it stopped working.
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Old 01-26-2021, 12:42 PM   #8
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Hey deprived,
Yes, as has been stated, you can use an alternate 12V source for your tests. 12v is 12v, no matter what the source is. You can hook up a hundred batteries in a row, you'll still get 12V at the end. Annnnnywaaaay, I just thought I'd throw a little schematic at ya that I drew up a few decades ago when we were towing our new Honda CRV 4WD EXL.
I didn't use a pre-made aftermarket harness. I just did what I'd been doing for decades in wiring toads and that was just wire it up, using only two diodes in the whole setup. I did however, use a 2 wire to three wire CURT tail light converter on the CRV side so that, my AMBER turn signals worked EXACTLY the same when towing it, as they did when driving it. And, I also got my third brake light to work on the CRV too.
Anyway, take a look at the drawing just for your own satisfaction and maybe understanding of your CRV.
Scott
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Old 01-26-2021, 12:46 PM   #9
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Okay -

So I stripped away a little bit of insulation right where the b/y/g wires inter the Hopkins unit and made sure the volts were getting there and they are.

I also checked to see if they were somehow grounding out. The ohms weren't zero but there's probably a little current going through the Hopkins/lightbulbs to ground.

At this point I am pretty sure the harness is toast unless you can think of anything else i can test.
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Old 01-26-2021, 01:08 PM   #10
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Hey deprived,
using only two diodes in the whole setup.
Wow - excellent diagram.

What kind of diodes would I use?

I'm pretty sure I may go your route now that I'm fairly sure the whole thing is a bust.
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Old 01-26-2021, 11:30 PM   #11
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Wow - excellent diagram.

What kind of diodes would I use?

I'm pretty sure I may go your route now that I'm fairly sure the whole thing is a bust.
Hey deprived,
Thanks for the nice comment. Way back a few millennia ago, I got regular old diodes from Radio Shack. They'd cost me about $4.00 for a 4-pack of them. But, now days, I just get them from Amazon. There's nothing special about them. Below is an example of what can be used.

https://www.amazon.com/MCIGICM-15SQ0...1724457&sr=8-5

Wiring toads up for towing is actually quite easy. Well I should say, the *older* toads. Todays newer ones have way more sophisticated wiring and don't accept anybody mingling with them. For the later toads, like our '15 Jeep JKUR, a Hopkins harness was the ONLY way to go.

But, for an earlier CRV, as in around '11, '12, '13 or so, they're easy to wire. If you follow that diagram, you'll be just fine. Some folks don't like messing with the factory wiring 'cause they think their toads gonna go up in flames. Well, everyone has limits as to what they're capable of and they should, and shouldn't mingle with.
Scott

P.S. I forgot to add, other than the 6-pin Cole Herse plug that was installed in the front of the CRV, all the wiring, including adding the 2-wire to 3-wire tail light converter, was all done right behind the left tail light. I pulled that whole tail light housing and did all the wiring right there, with the exception of tying into the right side for its operation. I ran those wires out the bottom side of the left side, across the bottom and up into the right side, no biggie. Just be sure you solder accurately and then tape/well insulate to your satisfaction.
Scott
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Old 01-27-2021, 08:37 AM   #12
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for an earlier CRV, as in around '11, '12, '13 or so, they're easy to wire.
We have a '14, and the wiring doesn't look too complicated - I think it's basically the same as the 11-13 models.

To be honest, I'm really surprised our Hopkins harness took a dump after only a few years use. I'm looking forward to a solution that is maybe a little more reliable.
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Old 01-27-2021, 11:19 AM   #13
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Originally Posted by deprived View Post
We have a '14, and the wiring doesn't look too complicated - I think it's basically the same as the 11-13 models.

To be honest, I'm really surprised our Hopkins harness took a dump after only a few years use. I'm looking forward to a solution that is maybe a little more reliable.
Yeah,
Who knows where they got the components to make up their harness's from. It's maybe a hit or miss thing. Some folks may get years and years out of an aftermarket harness. Others, well, maybe less than a couple of years. Good luck on your solution.
Scott
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Old 01-27-2021, 01:25 PM   #14
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I had a 2014 CRV that I used the Hopkins diode block/assembly. On a trip, I found that one of my brake/turn lights was out. The Hopkins unit had failed. I always carry a few spare diodes with me and just wired one in to get the light working again, bypassing part of the Hopkins unit.

The Hopkins units are cheap to buy, so I just bought another and moved on, rather than go through individual diodes.
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