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2006 Volvo VNL 780 Electrical gremlins


Capt-Kirk

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I hope someone on here can guide me to find these electrical issues i am having with the truck. 

1. Dome / map lights Driver's door red light, Drivers Map/Dome, Passenger's Map/Dome, passenger's red door lights don't work. Last December I replaced all the incandescent bulbs with LEDs and they worked fine. now they don't. The back condo lights work fine. 

2. The over head 12v accessory outlet over the driver's head has never worked since I bought the truck in October 2023.   The CB works fine. There are no active switches up there just blanks.

3. The Reverse lights quit coming on. The truck goes in to reverse just fine but no white lights on the tail. They used to work, then they became intermittent, now nothing.

 

Recent changes to the truck. 

I replaced the stereo. unplugged the amp. ran new speaker wire to all 4 speakers and sub woofer in back, and to the doors, and dash speakers.  This included a back up camera wired to the back up lights.  and a font camera that I wired to be always powered. After I installed the stereo it all worked as expected. Put it in reverse and the camera came on the stereo. when the truck was taken out of reverse the stereo would display the front camera for 20 seconds.  Now its nothing.

I bought a Binkley 3950 toy hauler. It has Dexter tow assist that waked up on the 12v accessory in the RV plug and Starts working with brake signal. It did not work at first. I looked in the Jack-a-lopee box and found the aux 12v was always on with key off. when the key was on it would turn off the aux 12v line. It was connected to 12v direct. I switched it to the 12v switched and not that works.  But the system is in limp mode Green light on top, orange on bottom.

I read the LCM. Light control module can shut these things down if it thinks there is a problem even though there is not. I don't have a service laptop to plug in and check. There used to be a LCM error on the center clearance light but that is gone. 

I also swapped the driver side door window crank for an electric lift motor and swapped the driver door window switch panel. It works fine unless I let the new switch run the window down automatically. The switch stays on for 7 seconds but is only takes 4 seconds to go down. the 20 amp fuse will blow if I don't catch it. i bought a microswitch to fix that problem latter. 

Another thing happened 3 weeks ago as were we camping in the truck waiting to puck up the 5th wheel, the truck low power cut off kicked in while we had too man lights on and the truck was off. I charged the batteries right away and did not notice any problems. 

I was expecting the dome/ Map lights fuse to be blown but i could not find one. and I could not find a fuse for the 12v overhead outlet. I checked all the fuses and none were blown. 

The fuse diagram label under the dash for the fuse block is gone. I tried looking it up on line but there are fuses listed where I don't have circuits. like the DIff lock. 

 

any help would be greatly appreciated 

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See that tall yellow relay in your fuse box.  Check it.  It is a double relay and controls power to a lot of the stuff you describe.  Also make sure your fuse 56 or 57 ( can’t remember which) is good because it fuses those circuits.

2006 Volvo 780 "Hoss" Volvo D12, 465hp, 1650 ft/lbs tq., ultrashift

Bed Build by "JW Morgan's Custom Welding"

2017 DRV 39DBRS3

2013 Smart Passion Coupe "Itty Bitty"

 

"Don't go around saying the world owes you a living. The world owes you nothing. It was here first!"

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Thank you for the response. 

How do you test that double relay with an ohm meter?

I found the dome light 10 amp fuse was popped.

The 12v over head outlet fuse 82. Was missing. I put in a 20 and nadda. I think the wires were disconnected when the truck was retired. They took out the qualcom/ volvo link and antenna. 

But the damn reverse light won't come on.  They spliced in to the harness on the left Chassis to the jackalopee. I followed it through 2 connectors forward and it's good. From the back, where does it go from there? Straight to the Trans or a computer?

 

Thank you 

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8 hours ago, Capt-Kirk said:

Thank you for the response. 

How do you test that double relay with an ohm meter?

I found the dome light 10 amp fuse was popped.

The 12v over head outlet fuse 82. Was missing. I put in a 20 and nadda. I think the wires were disconnected when the truck was retired. They took out the qualcom/ volvo link and antenna. 

But the damn reverse light won't come on.  They spliced in to the harness on the left Chassis to the jackalopee. I followed it through 2 connectors forward and it's good. From the back, where does it go from there? Straight to the Trans or a computer?

 

Thank you 

Sorry I’m not an electrician and mainly relied on a good friend NeverEasy on this forum to walk me through the diagnostics.  Chet loves electrical challenges and will hopefully see your post and chime in.  I do know he is having some health issues so may not be responding.  Maybe others can help.  I do know he solved my issues several months ago and that relay was the majority of the issue.  It is expensive so replacing without testing is not advised.

2006 Volvo 780 "Hoss" Volvo D12, 465hp, 1650 ft/lbs tq., ultrashift

Bed Build by "JW Morgan's Custom Welding"

2017 DRV 39DBRS3

2013 Smart Passion Coupe "Itty Bitty"

 

"Don't go around saying the world owes you a living. The world owes you nothing. It was here first!"

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  • 2 weeks later...

Found this:

I posted on the garage forum about no power to my cigar/12volt plugs in dash and no power to dome lights or CB power studs. I think I’ve narrowed it down to the battery protection relay being bad. I have checked and cleaned all battery connections as well as new O connectors with dielectric grease. Cleaned all grounds. Now to the relay. My Volvo is 2006 VNL780 and the relay is in the dash and labeled “Volvo 20458848 05W38” on the yellow top sticker. It is a five pin relay with no diagram on the body of the relay and the pins are lettered A,B,C,D,E instead of numbered like usual. I believe A & C correspond to 85 & 86, C to 30, D to 87, and E to 87A. In testing, I am showing no resistance across A & C and no click when 12 volt applied. Also no readings across D to C, or E to C. That’s the background. Now to the questions: 1. Anyone have a diagram of this relay or does my assumption seem right? 2. The 20458848 is the part number but all I can find online is the number with 08W43. Does that matter?

 

Found the solution to my issue. The battery protection circuit is governed by the LECM (Living environment control module). It involves fuse 52 and Relays 21 and 44. 44 is a tall one with a yellow Volvo sticker. That relay is double coiled and is energized from R21 through pin 85. I found R44 was defective and also fuse 52 had been removed when the shop was working on my ECM problem (I assume during) troubleshooting. It was never replaced. New relay and 5 amp fuse and everything working.

2006 Volvo VNL 780, " Arvey"  Volvo D12, 465hp, 1650 ft/lbs tq., ultrashift

2003 Jeep Wrangler Rubicon

2010 Forest River Coachman Freedom Express 280RLS

Jackalopee

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My problem was missing fuses. Seems the driver window fuse kept blowing due to new switch with auto down function held the motor on too long and blew the fuse so other 20 am fuses were taken to get the window back up.

Robb Peter to pay Paul then the pipper came back

 

I ordered that relay anyway just for a spare.

The reverse light was the transmission reverse switch.

And I replaced the battery disconnect switch, clean and protected all the connections. 

Thanks for all the reply and information. 

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