Headlight Gremlin - Update- Mystery Solved

[Alie&Jim's Carrilite]

Here is the scenerio-

Truck is a 1998 Volvo VNL 610

Drivers side low beam headlight doesn't operate.  Passenger side does.

Swap bulbs side to side- issues stays on drivers side.

High Beams work on BOTH sides.

Fuses are visually good.

New headlight harnesses from Deep Space lighting AKA our resident guru David Dixon.  No issues for 3 years.  Harness ohms out correctly.  

Is there a relay I'm missing?

Suggestions

Edited August 28, 2021 by Alie&Jim's Carrilite

[rickeieio]

I'd start by looking at the harness near the driver side hood hinge.  Likely pinch point there, and a handy place to stand when doing service.  Feel for pinched/crushed wires.

[Nigel]

I don’t know what David is doing for the first generation headlights but I did have a ballast go bad on one of mine.  

I think David had me remove both headlight assemblies and plug them in on the opposite side to confirm the problem was inside the assembly.  I had already changed the bulbs left and right like you have.

Nigel

Edited August 28, 2021 by Nigel

[Alie&Jim's Carrilite]

Update!

On my headlights, they are the T2 type bulb socket. The harness end that the bulb plugs into has 3 wires, ground and 2 powers.  When connecting the harness plug to the bulb, the low beam power wire was pushing up out of the socket instead of connecting onto the bulb connector.  Connector is only 23 years old....

[Nuke-E]

Jim,

Other places that might cause trouble include the daytime running light module, DRL relay, master light switch, as well as the interrupt switch and dimmer switch. The basic functions (high and low beam, not including flash to pass or DRL) are essentially kept separate left and right starting at the fuse box), which means that one side working doesn't let you rule anything out.  The fact that both high beams work does help quite a bit. I'm assuming no power at all at the terminal at the bulb connector.

Since high beams work on both sides (I assume fully switched on--flash to pass is a different circuit), you know both circuits (left and right) are getting power from the fuse box. That should also mean that the master lighting switch is OK--if only flash-to-pass works on both sides, hone on on the master lighting switch first.  It has two sets of contacts, one for the left and one for the right, each carrying current for high and low beam.

From there, the left and right side power heads to the dimmer switch, with the right (passenger) side having a splice along the way to feed the DRL relay coil.  Again, if high beams switched fully on work, everything should be ok through that splice to the dimmer switch.  Check the output of the dimmer switch--low beam for the driver's side will be terminal A.  If there's no power there with low beams on, replace the dimmer switch.

Now here's where it gets interesting (confusing might be a better word...).  When the master light control is switched off, the DRL relay is not energized, and power passes from 87A to 30 on the DRL relay.  Power to 87A comes from the DRL module (which looks almost identical to a normal 5-pin relay, just a little taller). The DRL module, when activated, puts out a reduced voltage on its pin 87A that feeds both low beam filaments. Check to see if the DRLs work (key on, parking brake released, headlight switch off). If you're getting low voltage (i.e. 9V or so) on the passenger side low beam, the relay could be stuck and powering the passenger side from the DRL module with a more convoluted series of failures.

The fact that your passenger side low beam seems to be working with the parking brake set suggests that the DRL relay is operating properly.  If it were stuck on, you'd have either a working driver's side headlight also (or a problem with the left side circuitry after the DRL module splice SR4 also). If it were stuck off, you wouldn't have a passenger side low beam with the parking brake on.

Back to the DRLs--if both DRLs work, you have a problem between the dimmer switch and splice SR4. Either the dimmer switch itself, the connector, or the splice has failed. If still only the passenger side DRL works, the problem lies between SR4 and the bulb. There are 3 connectors between the splice and the bulb, not including the one at the bulb itself.

If you're working solo, you could pull the DRL relay or the DRL module and supply power to terminal 87A.  Both headlights should come on. If the left side still doesn't, you're back to a problem between SR4 and the bulb. Otherwise, back to the dimmer switch.

This all presumes you only have one failure--there are a few scenarios where I could see a failed relay and DRL module or something getting to the behavior you're after, but it's far more likely that it's the dimmer switch or a harness problem.

 

 

Mark Bruss has the schematics on his site: http://www.dmbruss.com/images/Schematics/V5_PV776_370_99218_2_Headlights_VN_B5_99.pdf

http://www.dmbruss.com/images/Schematics/V4_PV776_370_98218_2_Headlights_VN_B2_98.pdf

Note that the pinouts for the '99+ DRL module are wrong. The ones in the older diagram are correct for both sets of build dates.

Edited August 28, 2021 by Nuke-E

[Nuke-E]

5 minutes ago, Alie&Jim's Carrilite said:

Update!

On my headlights, they are the T2 type bulb socket. The harness end that the bulb plugs into has 3 wires, ground and 2 powers.  When connecting the harness plug to the bulb, the low beam power wire was pushing up out of the socket instead of connecting onto the bulb connector.  Connector is only 23 years old....

If you need a quick fix, you should be able to pry up the release tab on the contact and get it back in place.  If not, any auto parts store should have the connector with a pigtail.

[Nuke-E]

2 hours ago, rickeieio said:

I'd start by looking at the harness near the driver side hood hinge.  Likely pinch point there, and a handy place to stand when doing service.  Feel for pinched/crushed wires.

I've talked about this before--especially on the 2nd gen Volvos, this is a common failure point.  Catching the hood hinge, cut zip ties from service work/bumper repair, etc., can either pinch the harness or leave it vulnerable to chafing on the bumper bracket.  If it gets loose on the run across the lower edge of the hood, it can also be split in half by the torsion bars that help support the hood.

It should be a somewhat regular inspection task to examine that part of the harness. It only takes a small rub to let corrosion get started, and I've seen where more than a foot and a half of wire needed to be replaced by the time the light failed.  If you're lucky, the first wire to break is a turn signal, parking light, or temperature sensor wire; if you're really unlucky, the ground wire breaks first and everything attached to the hood goes dark.

It was dumb luck the first time I stumbled upon it, but I've lost count of how many times I've seen it since.

[Alie&Jim's Carrilite]

Thanks David! The DRL module was removed when it caused issues in the past.  

[rickeieio]

In the interest of full disclosure, I knew about the harness issue because I was paying attention when David was explaining it to someone.