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Lost left turn signal [message #371051]

Mon, 06 February 2023 18:59

Larry

Messages: 2875
Registered: January 2004
Location: Menomonie, WI

Karma: 10

Senior Member

So, something happened to me and I just want to put it out there in case it happens to anyone else. Traveling between Okeechobee Florida and Melbourne Beach Florida we were driving in a hard rain. I suddenly had no left turn signal with the headlights on but had a steady left TS dash light. Turn the headlights off and TS worked just fine. So, to make a left turn or left lane change, I had to turn the head lights off to use the left signal. Right TS worked fine headlights on or off.
So, our headlights and running/TS light are mounted in a fiberglass fender, so they must be provided with a ground back to the aluminum body or frame in order to complete the circuit. Ya know, electrically speaking when you loose a ground, weird things can happen. Never did find the broken ground wire. To correct the issue, I ran a piece of wire from the turn signal body to the aluminum chassis. Had to do it in Red because is all I had at the moment. Plan to change it to black when we get home.

Anyway, Just FYI to everyone.

Larry

78 Royale w/500 Caddy
Menomonie, WI.

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Re: Lost left turn signal [message #371053 is a reply to message #371051]

Mon, 06 February 2023 20:53

RF_Burns

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

Karma: 3

Senior Member

Could also be that you had no or dim headlight as well. When you turned OFF the headlights, the turn signal found a ground back through the headlight filament or the ground was was low enough resistance to operate the turn signal, but not the headlight and turn-signal.

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: Lost left turn signal [message #371054 is a reply to message #371053]

Mon, 06 February 2023 22:06

Larry

Messages: 2875
Registered: January 2004
Location: Menomonie, WI

Karma: 10

Senior Member

RF_Burns wrote on Mon, 06 February 2023 20:53

Could also be that you had no or dim headlight as well. When you turned OFF the headlights, the turn signal found a ground back through the headlight filament or the ground was was low enough resistance to operate the turn signal, but not the headlight and turn-signal.

Yup, that's what's weird about loosing a ground. Thanks for that explanation.

Larry

78 Royale w/500 Caddy
Menomonie, WI.

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Re: Lost left turn signal [message #371056 is a reply to message #371051]

Fri, 10 February 2023 15:56

Russell K.

Messages: 178
Registered: October 2016
Location: Dunedin, Florida

Karma: 4

Senior Member

Hi Larry,
I had a very similar problem recently, losing all blinkers and flashers, only with the lights on. They work fine with the lights off. Which corner of the coach did you run the new ground wire from the turn signal body to ground. Did you ground all four corners? or one front and one back?

Thanks,
Russell

1978 Eleganza II, Dunedin, Florida

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Re: Lost left turn signal [message #371057 is a reply to message #371056]

Fri, 10 February 2023 16:50

Larry

Messages: 2875
Registered: January 2004
Location: Menomonie, WI

Karma: 10

Senior Member

Russell K. wrote on Fri, 10 February 2023 15:56

Hi Larry,
I had a very similar problem recently, losing all blinkers and flashers, only with the lights on. They work fine with the lights off. Which corner of the coach did you run the new ground wire from the turn signal body to ground. Did you ground all four corners? or one front and one back?

Thanks,
Russell

So far I've done this twice now. Both front turn signals. Passenger front I went from TS body to Aluminum plate that the combiner is mounted on under the right hatch. Drivers front I went from TS body to the back side of the foot well near the brake booster. When I get home and have access to tools and wire, I will be changing the passenger TS to grounding it on the Aluminum plate as Ken Burton suggested. Your situation sounds a little more complicated and I will differ to Ken on this.

Larry

78 Royale w/500 Caddy
Menomonie, WI.

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Re: Lost left turn signal [message #371058 is a reply to message #371056]

Sat, 11 February 2023 19:06

Ken Burton

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

Karma: 10

Senior Member

Larry and Bruce,

I just spent an hour digging through through 3 GMC wiring diagrams a 73, a 78, and a transmode. All were equally lacking as far a grounds go. As an example, one place they show one connection with 7 wires on it and a 10 ga. wire going to ground symbol. Where that is located in anyone's guess. The do show the heavy braided jumpers I was talking about in the very top right of the diagrams.

So I can not tell you much more than I learned 15 years ago. If I haven't physically had to go there in the past to fix something, then the GM documentation I looked at does not help us much.

Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

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Re: Lost left turn signal [message #371059 is a reply to message #371051]

Sun, 12 February 2023 08:35

RF_Burns

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

Karma: 3

Senior Member

Ken,
Thanks for your input. The GMC Assembly Manual does show some electrical wiring ground points. However because I have only the scanned downloaded version it is not searchable nor very clear... not that the paper version is searchable either.

However we are only dealing with low current DC grounds. When troubleshooting and find that a bad ground is the cause of a problem, in most cases another wire can be spliced in and grounded to a convenient point. Note this is only true for low current items like lighting etc. High current items such as the main battery ground must go to the engine block.

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Re: Lost left turn signal [message #371060 is a reply to message #371059]

Sun, 12 February 2023 20:15

Ken Burton

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

Karma: 10

Senior Member

While true and it will work. What happens when one of those high current grounds goes away and everything tries to go down the new wire one you added. Poof. Instant smoke. I use to have a demonstration of what could happen if you grounded the distributor to the battery instead of the engine block. Then disconnect the negative battery cable simulating a dirty battery cable. Now crank the starter. Instant smoke. I am just trying to prevent future problems for someone If / when one of those cross connect jumpers degrades and looses contact which is not unusual.

Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

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Re: Lost left turn signal [message #371061 is a reply to message #371051]

Sun, 12 February 2023 21:12

RF_Burns

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

Karma: 3

Senior Member

Hi Ken,
I was saying that a low current ground from something like a clearance light etc, could have a new ground installed to the body, while a high current ground like the main battery ground MUST goto the engine block. If the main battery ground was lost, then the engine block would be pulled up towards battery 12V+ when the starter was activated. The body and frame would also follow the engine block voltage and everything would brown-out.

There is an OEM ground wire from the battery terminal going to the aluminum plate and then a wire going to the dash, but from my observations these are mounted to the SMC so are separate from the body grounding, so high starter current cannot find its way to this ground.

My concern is for those who ground the battery negative to the chassis frame. All kinds of nasty things can happen when the starter current tries to find a return path.

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Re: Lost left turn signal [message #371062 is a reply to message #371051]

Mon, 13 February 2023 11:11

Tom Katzenberger

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

Karma: 4

Senior Member

Larry,

I stopped by Jeff's in Okeechobee, Jeff said I just missed you guys by a week or so. I just got back to Maryland from the Florida Keys this past Friday. Hopefully we will see you and Lucy in Mississippi.

As far as grounds go, I had LED/tail light scooter carrier problems which I corrected via the input from Ken and the guys. I still don't know what was wrong and where, but I do know that I added grounds and now all works well. I still scratch my head about what ground was bad, but if it works don't fix it I guess, LOL.

Take care all,
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: Lost left turn signal [message #371063 is a reply to message #371061]

Mon, 13 February 2023 23:15

Ken Burton

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

Karma: 10

Senior Member

Bruce,

I agree with everything you posted. I have been known to cheat occasionally and I usually get burned later. When I installed my Macerator I just grounded it under a mounting bolt which is the steel frame. It worked for about 5 years and then the rust on the frame set in. It took me a while looking at other stuff before I discovered it was the ground connection. I ran the ground wire to where it belonged in the first place and took care of the problem.

I did the same thing on my Colorado when I installed 7 pin trailer connector. I ran the ground to the frame. Several years later I lost all trailer lighting due to a bad ground. It turns out the bed and the steel frame are not ground and whatever was giving it the circuit went away. The factory wiring harness for the 4 pin connector ran the ground all the way back up front. I needed a heavier ground for the 7 pin to run a winch on one of my trailers. It worked for a while.

These are some of the reasons I tell people to do it the correct way the first time.

Ken B.

Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

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