| Parking Light Circuit - Heavy Current Draw [message #346594] |
Sun, 18 August 2019 16:31  |
Christo
Messages: 109
Registered: April 2019
Location: Weymouth, MA
Karma: 0
|
Senior Member |
|
|
Looks like it's electrical gremlin day on GMCforum! Here's another one: While on an excursion this weekend I turned on my parking lights and noticed a significant voltage drop (.5 to 1 volt below the normal 13.5). I haven't driven the coach much at night since acquiring it four months ago, so I don't know if this is a new problem. However, I did notice something new the other day -- my left front clearance light isn't working. The final symptom is that the headlight switch rod (that the knob attaches to) is getting very hot -- consistent with high current draw. I won't be using the lights any more until this problem is addressed!
My first suspicion is a partial short in the clearance light due to corrosion that draws a lot of current but not enough to blow a fuse. I consulted the service manual and it looks like it would be straightforward to unplug the connector to the front clearance lights to see if this isolates the problem. Another potential trouble spot is that I recently pulled down the inside rear cap to install a backup camera, and as luck would have it I chose to wire it into the rear clearance light circuit. As suspicious as that sounds, I don't believe it's the root cause. The camera and rear clearance lights are working fine and the camera doesn't draw much current. Nevertheless, the wiring back there did get disturbed.
I would welcome any advice about common problems that these symptoms point to, diagnostic approach, etc. Thanks!
Christo Darsch
GMC Nor'easters
1977 Eleganza II - "The Komet"
3.50 Power Drive, Disc Brakes, Alcoas
Weymouth, MA
|
|
|
|
| Re: Parking Light Circuit - Heavy Current Draw [message #346603 is a reply to message #346594] |
Sun, 18 August 2019 23:44  |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
|
Senior Member |
|
|
I think your approach is right on. Every parking light problem I have ever chased on a GMC ended up being a corroded / rusted clearance light(s). Obviously it still could be a tail light, or side marker, or parking light.
As a side note every GMC clearance light I have worked on had the + and minus reversed. So the outside frame was at +12 volts instead of ground. That will not cause your immediate problem, but should be noted if you choose to change the clearance lights to an LED type.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
|
|
|
|
| Re: Parking Light Circuit - Heavy Current Draw [message #346604 is a reply to message #346603] |
Mon, 19 August 2019 06:14 |
C Boyd
Messages: 2629
Registered: April 2006
Karma: 18
|
Senior Member |
|
|
Or license plate light.
Ken Burton wrote on Mon, 19 August 2019 00:44I think your approach is right on. Every parking light problem I have ever chased on a GMC ended up being a corroded / rusted clearance light(s). Obviously it still could be a tail light, or side marker, or parking light.
As a side note every GMC clearance light I have worked on had the + and minus reversed. So the outside frame was at +12 volts instead of ground. That will not cause your immediate problem, but should be noted if you choose to change the clearance lights to an LED type.
C. Boyd
76 Crestmont
East Tennessee
|
|
|
|
|
|
|
|
| Re: Parking Light Circuit - Heavy Current Draw [message #346636 is a reply to message #346627] |
Tue, 20 August 2019 09:12 |
Christo
Messages: 109
Registered: April 2019
Location: Weymouth, MA
Karma: 0
|
Senior Member |
|
|
Great tip, John! By the way, if my apparently burned out bulb/fixture isn't the source of the problem, I'd still like to unplug the main connector to the front clearance lights to narrow down the problem area. Where specifically do I find that connector?
Christo Darsch
GMC Nor'easters
1977 Eleganza II - "The Komet"
3.50 Power Drive, Disc Brakes, Alcoas
Weymouth, MA
|
|
|
|
| Re: Parking Light Circuit - Heavy Current Draw [message #346666 is a reply to message #346636] |
Tue, 20 August 2019 18:03 |
 |
Tom Lins
Messages: 372
Registered: February 2004
Location: St Augustine, FL
Karma: 1
|
Senior Member |
|
|
Christo wrote on Tue, 20 August 2019 10:12Great tip, John! By the way, if my apparently burned out bulb/fixture isn't the source of the problem, I'd still like to unplug the main connector to the front clearance lights to narrow down the problem area. Where specifically do I find that connector?
According to the wiring diagram it is a 8 pin connector "Under the instrument Panel Upper LH side"
Tom Lins
St Augustine, FL
77 GM Rear Twin, Dry Bath, 455, Aluminum Radiator Quad-Bag Suspension Solar Panel
Manuals on DVD
YOUTUBE Channel: GMC Dealer Training Tapes
http://www.bdub.net/tomlins/
|
|
|
|
| Re: Parking Light Circuit - Heavy Current Draw [message #346673 is a reply to message #346594] |
Tue, 20 August 2019 21:00 |
Christo
Messages: 109
Registered: April 2019
Location: Weymouth, MA
Karma: 0
|
Senior Member |
|
|
Well, I couldn't find the 8 pin connector to the front clearance lights by looking under the dash, and I didn't want to pull the instrument panel, so I went ahead and opened up the recently inoperative left front clearance light. It's an LED unit from 2010 and there was about 2.5 inches of corroded ground wire wrapped around one of the mounting screws. The high current draw mystery is solved; welcome to Jankyville. Replacement lights are on the way.
Christo Darsch
GMC Nor'easters
1977 Eleganza II - "The Komet"
3.50 Power Drive, Disc Brakes, Alcoas
Weymouth, MA
|
|
|
|
GMCforum
Search
Help
Register
Login
Home
