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5 Volts Bleeding to Opposite Turn Signal [message #370971]

Tue, 10 January 2023 16:01

Tom Katzenberger

Messages: 399
Registered: June 2019
Location: Kingsville, MD

Karma: 4

Senior Member

Hello all,

I am installing a LED light bar across the rear scooter carrier. I am trying to defend myself, as much as possible, against those who text and drive, (i.e. rear end collision).

There is a blead of 5 volts which strays to the opposite signal. Not enough to fully light the filaments in the original bulbs, but plenty to light the light bar.

I was thinking Diode but I don't even know where the current would be crossing. Therefore I don't even now where to put the Diode. Has anyone else come across this problem? If so any tips and tricks would be welcome.

Thanks to all and have a great evening.

Take care,
Tom K.

Tom & Oki Katzenberger, Kingsville, Maryland, 1977 23' Birchaven, 455 C.I.D., Micro Level, Howell EBL-EFI Spark Control, Macerator, York Air Compressor, 6 Wheel Disc, Quadra Bag, Onan W/Bovee Ignition

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Re: 5 Volts Bleeding to Opposite Turn Signal [message #370972 is a reply to message #370971]

Tue, 10 January 2023 16:24

Tom Katzenberger

Messages: 399
Registered: June 2019
Location: Kingsville, MD

Karma: 4

Senior Member

Guys,

I think I have a bad ground in the original trailer wire. Not sure if it is in the terminal connections or somewhere along the wire?

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Re: 5 Volts Bleeding to Opposite Turn Signal [message #370973 is a reply to message #370971]

Tue, 10 January 2023 20:59

RF_Burns

Messages: 2276
Registered: June 2008
Location: S. Ontario, Canada

Karma: 3

Senior Member

I know that early 3rd stop lights had a diode in series with each of the Stop/Turn lights. That caused the 3rd stop light to flash if only a turn sign was ON, but would be constantly ON if there was a brake light ON.

The opposite diode would prevent voltage from "Leaking" to the other Stop/turn light.

Can you post a wiring diagram that came with the 3rd stop light so I could see the wiring.

Thanks

Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that

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Re: 5 Volts Bleeding to Opposite Turn Signal [message #370974 is a reply to message #370971]

Wed, 11 January 2023 09:17

Tom Katzenberger

Messages: 399
Registered: June 2019
Location: Kingsville, MD

Karma: 4

Senior Member

Bruce,

Attached is the LED bar that I purchased from Amazon:

https://www.amazon.com/dp/B0888T79RP?psc=1&ref=ppx_yo2ov_dt_b_product_details

I cut the 4 pin flat connector and connected the LED bar to the 7 pin round connector with the other trailer lights.

I had everything working, I just couldn't stop the electric bleeding to the opposite LED turn signal and got both signals flashing. The intended signal did flash much brighter.

Thank you for any assistance as I am an electronic idiot.

Take care and thanks again Bruce.

Sincerely,
Tom K.

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Re: 5 Volts Bleeding to Opposite Turn Signal [message #370975 is a reply to message #370972]

Thu, 12 January 2023 02:55

Ken Burton

Messages: 10030
Registered: January 2004
Location: Hebron, Indiana

Karma: 10

Senior Member

Tom Katzenberger wrote on Tue, 10 January 2023 16:24

Guys,

I think I have a bad ground in the original trailer wire. Not sure if it is in the terminal connections or somewhere along the wire?

GMC grounds are not what you might expect. I have found that they are not like days of old when everything is connected to the frame. They are also not the same on some newer GM vehicles too. We use to use the vehicle frame as a central connection point for all grounds, but that is NOT true on a GMC motorhome. The master ground for a GMC (engine side) and everything powered by the alternator is the engine block. So everything 12 volt powered needs a direct as possible path back to the engine. The ground for the tail lights, clearance lights, and brake / turn signals is the engine and NOT the frame or body. If yours is a ground problem, which it very well might be, I will bet your trailer wiring harness connector ground pin is not connected to the correct ground return wire going to the engine.

That said, there is suppose to be a braided jumper from the back of the transmission to the steel frame of the coach. If your trailer wring connector is connected to the frame, or worse yet the body, Then the ground return path goes through that jumper instead of the direct to engine wire like rest of the lights. It is common for those jumpers to be left disconnected when the trans is worked on or for them to be degraded over the years and no longer be functional.

So check where the ground terminal of the trailer connector is connected to. Move it to the ground return wire used by the tail lights if necessary. I do not remember the color of that wire for sure, but I think it is white.

Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

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Re: 5 Volts Bleeding to Opposite Turn Signal [message #370976 is a reply to message #370971]

Thu, 12 January 2023 08:56

Tom Katzenberger

Messages: 399
Registered: June 2019
Location: Kingsville, MD

Karma: 4

Senior Member

Thank you Ken,

I still have the original braded ground strap from the engine to the frame. I also swaged an additional ground cable from the engine to the frame just to make sure the ground was good.

I will trace the trailer light cable back because as I remember the trailer connection ground went to the steering column. You may have bumped me in the direction of a possible solution, I will know tonight when I get back in the shop.

Thank you again and take care,
Tom K.

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Re: 5 Volts Bleeding to Opposite Turn Signal [message #370977 is a reply to message #370971]

Thu, 12 January 2023 15:48

Tom Katzenberger

Messages: 399
Registered: June 2019
Location: Kingsville, MD

Karma: 4

Senior Member

Good evening gentlemen,

I found that when I plug the trailer connection in I get 6 volts coming back from the brake light wire. I think this is where my problem is.

Any thoughts?

Take care,
Tom K.

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Re: 5 Volts Bleeding to Opposite Turn Signal [message #370978 is a reply to message #370971]

Thu, 12 January 2023 16:25

Tom Katzenberger

Messages: 399
Registered: June 2019
Location: Kingsville, MD

Karma: 4

Senior Member

Ken and Bruce,

I wish I could tell you something profound, but I checked the grounds and installed a new trailer plug. After which everything works? I don't know if it was the ground or the plug, but I am just very happy everything works.

Again, thank you guys for your help.

Take care,
Tom K.

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Re: 5 Volts Bleeding to Opposite Turn Signal [message #370979 is a reply to message #370978]

Fri, 13 January 2023 03:06

Ken Burton

Messages: 10030
Registered: January 2004
Location: Hebron, Indiana

Karma: 10

Senior Member

Well it was a bad guess on my part but you got it fixed and that is what counts. I hope I did not lead you a stray. Remote diagnosis is a bear at times and not always correct.

Ken

Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

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Re: 5 Volts Bleeding to Opposite Turn Signal [message #370981 is a reply to message #370971]

Fri, 13 January 2023 11:13

Tom Katzenberger

Messages: 399
Registered: June 2019
Location: Kingsville, MD

Karma: 4

Senior Member

Ken,

Your help is ALWAYS greatly appreciated! When I say thank you I mean it. You guys are great. You have a wonderful weekend.

Take care,
Tom K.

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