LH Highbeam not working

[Kazza]

Hi guys - not very electrically inclined and looking for some help diagnosing my non-functioning LH (driver side) highbeam.

 

Things I've already checked:

Bulbs - Highbeam filaments are fine on both bulbs. Switched them round to confirm this.

Headlamp relays - Tested OK

Headlamp Fuses - Not tested but based on the wiring diagram if one of these were blown the headlamp would not operate at all  in high or low so I assume this is not the problem.

DRL module - I believe this is fine.. I had issues with low beams and DRL mode previously so I took the module apart and re-soldered all the suspect connections. This fixed all issues apart from LH highbeam. I also tried another DRL module from the scrapyard and it gave me full functionality apart from LH highbeam. Small chance both DRL's have the exact same issue!

Combination Light Switch - I checked the connections on the switch and was getting continuity across the correct pins relative to the position of the switch/stick in all cases. So this seems fine.

 

Now I've been testing continuity in the wiring harnesses. Upon testing the DRL to light switch I'm getting continuity at the correct terminals for LH Highbeam. However, upon testing the bulb socket to the DRL I seem to be getting continuity at a number of different terminals which seems very odd in my limited knowledge/experience of circuitry.

 

Referring to the illustration HERE..

 

I am getting continuity at LH bulb socket terminal 1 (highbeam) to DRL terminal 10.. this is what I expect. However, I am also getting continuity from LH bulb socket terminal 1 to DRL terminals 12, 15, 16 and 17.

 

I have studied the headlight operational guide a few pages back in the FSM and it doesn't seem to make sense for all these wires to be connected. So out of interest I checked RH bulb socket terminal 1 (highbeam) and it registers continuity only at DRL terminal 9 which is the correct path of the wire.

 

So... my current diagnosis is that I have a number of wires in the harness going from the LH bulb socket to the DRL module that are interconnecting when they shouldn't be and this is causing non-function of the LH highbeam somehow when the circuit is live (voltage applied).

 

Can somebody with better electrical knowledge than me tell me if I'm barking up the right tree here and what would you recommend as next steps?

 

[Kazza]

OK - so it looks like I have solved the problem.

 

Upon closer inspection of the wiring harness coming out of the LH bulb socket I noticed there had been some jiggery pokery on it. After peeling back the electrical tape its pretty obvious the bulb socket had been replaced. The original wiring had been soldered to new wires leading to the socket about an inch out of the socket itself. Strangely a random 3 inch ground wire had been spliced into the LH high beam wire and was grounding directly under big black air intake box holding the air filter. I accidentally ripped this wire from its grounding point and then just figured i do the continuity test again with it disconnected and the LH high beam terminal was now only showing continuity to the correct terminal on the DRL. So then i hooked everything back up (minus the jerry rigged ground wire) and hey presto... LH highbeam works again!

 

My guess is this modification was done in an attempt to solve issues that were actually related to the DRL module being faulty.

[Kazza]

Spoke too soon - after putting everything back and fully testing all the light positions against a wall with the engine running I noticed that the LH bulb was not as bright at the the RH bulb. I then noticed that actually the opposite filaments were lighting up in either bulb at each switch position! It then occurred to me... the person that replaced the LH bulb socket has wired up low and high beam terminals incorrectly, they have been swapped round. I should have noticed this when checking continuity during my troubleshooting but I was distracted by the weird readings described in my original post and totally overlooked that i actually had terminals 1 and 2 mixed up on the bulb socket based on the FSM diagram.

 

My testing had..

 

Switch OFF or Sidelights (DRL Mode) - LH lowbeam half power / RH highbeam half power

Auto or Lowbeam on - LH highbeam half power/ RH lowbeam full power

Highbeam on - LH lowbeam full / RH highbeam full

 

I guess I need to rewire this plug back round to the correct layout. What a nightmare this has been.. I thought I was useless with electrics!

[Slartibartfast]

Ain't wiring fun? Good job tracking it down. Clearly you're better at it than the last guy!

[Kazza]

Latest update...

 

After switching the wiring for terminals 1 and 2 (high and low beam) on the LH bulb socket, the correct filament is now lighting up in the LH bulb for both high and low beam settings BUT when I have my high beams on the LH bulb filament is not producing the same light output as the RH filament.

 

Re-testing light switch positions has the following;

 

Switch OFF or Sidelights (DRL Mode) - LH lowbeam low power / RH highbeam low power

Auto or Lowbeam on - LH lowbeam full power / RH lowbeam full power

Highbeam on - LH highbeam mid power*** / RH highbeam full power.   

*** note that in this setting LH highbeam is producing a higher output than in DRL mode but not the same full power output as the RH highbeam.

 

So I still have a problem... can anyone chime in on this? Every setting on the combination light switch works but the LH highbeam filament is producing a lower brightness when highbeam is switched on. I have swapped the bulbs around again and bulbs are OK. Perhaps the jerry rigged ground mentioned in previous post was put in to compensate for poor grounding and a lower output in the bulb on the drivers side?

Edited October 5, 2019 by Kazza

[Mr_Reverse]

Sounds like a poor ground in the wiring to the left headlight. Now you know why us professional wrench monkeys charge so much for electrical issues. There is a lot of tedious labor involved.

[Kazza]

43 minutes ago, Mr_Reverse said:

Sounds like a poor ground in the wiring to the left headlight. Now you know why us professional wrench monkeys charge so much for electrical issues. There is a lot of tedious labor involved.

 

Couldn't agree more. So I guess I need to check the voltage across the ground side of the circuit at each point now...

[Mr_Reverse]

Might have to do a visual inspection of the wiring between the DRL module and left headlight socket. Probably a wire that got some damage that allowed water in and corrosion to form in the wire. If the low beam is getting full power, it might just be the high beam positive wire. If you feel comfortable with doing some minor damage to the wire, you can run a temporary jumper from near the connector at the DRL module to the headlight socket and see if the light gets full brightness. If so, you know there is a problem with that wire.