P500 Back up alarm switch

[makac132]

Hi guys, on Honda OEM accessory sub harness the Red output is for back up alarm.
The problem I have is that it’s hot all the time (D, N & R instead of R only). Anyone knows where the switch is
responsible for that? Thanks

 

[Hondasxs]

You are talking about the oem backup alarm harness addon?

Yes, it will be hot all the time. It works off a ground trigger.

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[makac132]

Hondasxs, yes I meant OEM back up harness add on.
So the + is on all the time and relay is controlled with ground (-).
My question is, once you shift into R, where do you pick up controlled ground,
so the back up alarm would come on only in Reverse? Where is the switch?

 

[Hondasxs]

After you install the harness at the transmission and run the hot line up front it then just works whenever in reverse.

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[jnmanz28]

THANKS Guys!! I didn't know this harness existed! I want to add a back up camera to my P500 so in theory it should work for the camera and alarm in the same manner. Looks like I'll be spending some more money.

 

[Hondasxs]

THANKS Guys!! I didn't know this harness existed! I want to add a back up camera to my P500 so in theory it should work for the camera and alarm in the same manner. Looks like I'll be spending some more money.

Remember it's a negative trigger.
Most cameras use positive triggers.
You will need to convert it.

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[makac132]

Thanks Hondasxs, I must be really dense. What do you mean by installing the harness at the transmission?
The harness I have is 08Z08-HL5-A00 it has 4 outputs (Green, Yellow, White & Red) and it plugs in to the main harness connector under the hood by the horizontal cross bar. Are we talking the same harness here? If we do, you run hot straight and where is the other side (ground) coming from?

 

[Hondasxs]

Oh.....
Welp....

This is the harness you need #08V71-HL5-A00. It is about $40.
You also need the harness you mentioned #08Z08-HL5-A00 $13. Or find your own key-on hot supply.


This part #08V71-HL5-A00 is the actual backup harness. The other is just the power supply.
This one installs to the transmission to collect the back up signal.
Its actually a lot of work to do.

 

[jnmanz28]

Remember it's a negative trigger.
Most cameras use positive triggers.
You will need to convert it.

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Oh.....
Welp....

This is the harness you need #08V71-HL5-A00. It is about $40.
You also need the harness you mentioned #08Z08-HL5-A00 $13. Or find your own key-on hot supply.


This part #08V71-HL5-A00 is the actual backup harness. The other is just the power supply.
This one installs to the transmission to collect the back up signal.
Its actually a lot of work to do.

View attachment 308828

Hondasxs, since the harness is a lot of work to do (not sure I'm qualified to handle install). Pretty mechanically inclined but.....

I'm wondering would there be another way to add the camera so it would trigger when in reverse without using the back harness?
I know something triggers the reverse light on the dash but don't have any idea where it is or if there is a way connect the camera to it. Sorry for all of the silly questions but the camera would really be handy to have on the trails, THANKS!

 

[Hondasxs]

You could tap the same wire near the computer with a posi-tap seal.
It would still be negative triggered.

This wire is the reverse gear position wire and is the only reason for that big connector I posted.

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[makac132]

Aaah, that’s what it is. Thank you Hondasxs, for a while I thought I’m loosing it. 🤭
It all makes sense now.

 

[makac132]

Hondasxs sorry to bother you but would you know how to identify the reverse gear position wire near the ECU you mentioned? I already have steady supply of +12V, proper 12V alarm so I only need the ground trigger to make it all work.

 

[Hondasxs]

I can only check a 2015 ECU currently.
For that year, it is pin A-25.
A is the big black connector.
Pin #25.
It will be a gray wire.

Most likely the same on all years.

Dont use those blue scosche taps.
Use a Posi-Tap or a T-tap.

 

[makac132]

Thanks Hondasxs, my Red Devil was born in 2017 but I bet the wiring is the same, I’ll check that.
Appreciate that very much. 🙏

 

[Hondasxs]

From there.. You will use that as your GROUND for small LED's.
Like a set of cubes or our backup lights (link below).
And your positive will be straight key-on or other source.
Then, whenever in reverse. POOF..
The light will come on.

You can add a switch to turn if OFF. To turn it off so it wont come on when in R.
But, you can NOT just add a ON switch. This will backfeed and confuse the ECU.
Suggestions are using a diode or some tricky wiring.

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[makac132]

Thanks Hondasxs, I thought of it as well. I plan to use ground triggered relay for that. On relay’s power side it will be business as usual, also plan to include Off switch on power side to switch it off alarm when not needed. By using relay ECU should be happy. Thanks again.

 

[jnmanz28]

Hondasxs THANKS also for all the info!!!
makac132 THANKS for asking the original question and allowing me to highjack your post somewhat!!!

This site has a GREAT group of guys with a WEALTH of knowledge!!!!!

 

[makac132]

Hondasxs I finally got some small T-tap connectors and looked at the ECU. As you already mentioned and I can now confirm that it’s the gray wire on A 25 pin of the middle ECU’s connector supplying the ground in Reverse (P500-2017). So I used it only for negative triggered relay’s control circuit. The power side of the relay is running LED lights and the alarm (beeper) that has OFF switch in series if I want to shut it off. The negative for that comes from battery. Here are some pics how I tapped in. Thank you for all your info.

 

[Hondasxs]

Nice.
What you did is fine. But next time consider switching the positive power with the negative trigger relay.
I just hate running constant power anywhere if I can help it. Lol.

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[makac132]

Hondasxs I think that’s what I did. Steady +12V is used only for the coil of negative triggered relay. On it’s load side it’s business as usual - negative going straight and the positive is controlled through tne NO contact. How else would you do it?