GMC28

right low beam fail - not bulb

25 posts in this topic

right low beam stopped working. No big deal, so replaced it.  Still didn't work. 

Hmm.

The filament on the old bulb actually looked ok too, so more evidence that something else is wrong.

Swapped left and right low beam fuses  (22 & 23), and no change (left low still works, and right low still dark), after noting that neither fuse looked bad to begin with.

Did a quick voltage check on the wire harness/connector at the bulb, and seems to be dead, though thats not 100% reliable because reaching in there is challenging (just did the quick change method to acces bulb from top.... have not removed the front end yet).  I got the probes into the sockets using braille, and should be a good check, but again, not 100% reliable check at this point.  Will go back to that later when the front is torn off.

Did some poking around on the forum for more ideas, and will do some more, but before I tear it apar I'm fishing for hot tips on what the issue might be.

 

next step would be Verifying that 22 & 23 are the correct fuses for the bulbs (i pulled the one fuse and the left low beam quit, so that appears to proof enough most likely).

Then i guess tear the front end off and start chasing wires.  Hopefully has some good smoking-gun type clues....?

 

cheers

 

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It's not the fuse.  It's the SAM.  Put in relays ASAP.  If one circuit is dead, use the good one and one powerful external relay to run both headlights.  There is a "How To" about this.  I wrote it. 

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thanks mike -

I think I have the right "how to" on that from you...  Oct 31, 2015?

Any advice on running down that replacement harness online?  Or is it true that if do as you've done, then I'm bypassing the harness anyway i suppose, so no need?

 

Nice write up, and most of it is pretty clear for me, but did you or do you have a quick sketch diagramming what you described?  the narrative and pics are excellent,  so its pretentious of me to ask for more,  but would like to confirm a couple things, and a rough sketch would be great, if you're game. 

Just if you're game...

either way, this is what i was looking for, so thanks again!

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actually mike, i may have just answered my final question, based on what you wrote in the other forum on this... I managed to miss that you're using the lead from the one good sam headlight circuit....

But, if the one good relay in the sam is still usable, what keeps a guy from just using that one relay to power both low beams by just tying the one sam output to both low beam wires at the harness?

 

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The wiring and relay are not robust enough to sustain a single headlight, the reason for your failure.  Doubling the load on a similar circuit would be a horrible idea.  While you are wiring in an extra relay for the headlights, you should do the same for the fuel pump, it is prone to failure as well.

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makes sense.

I'll grab some relays tomorrow.  Mike used 30a for the headlights... that sound ok for fuel relay as well?

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yes

 

i did this to a friends car...installed 3 relays...one for each low beam (both headlight relays fed from the one working output) and one for the fuel pump

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Some guys mentioned using a single relay and the new large gauge feed direct from battery as being fine for feeding both left and right beams (from the one relay).  Any reason not to do this, other than wanting the redundancy to not cause both beams to fail in case case a relay fails?

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Use two relays, separate relay each side. 

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If both circuits still work from the SAM, do have two separate relays, one for each light.  If you are lucky, the plug at the SAM has melted but the circuit is still OK.  If you are unlucky, the SAM is dead on the dead circuit. 

 

So, if only one low beam circuit works, run a single relay for both lights using the one good SAM circuit.  Current through the one good circuit should be lower because you're using an external relay, according to my understanding of how relayed circuits work.  That's the whole point of using relays.  But it's true, it's more risky to use one circuit than using both if one of the SAM circuits is not already dead.

 

You may need a repair harness for the melted plug.  The plastic melts and the contacts can move away from each other and you will need it to be unmelted if the second circuit still works.

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Posted (edited) · Report post

i had to cut the plug because the center part was too brittle and melted

 

i was able to save the pin from the one working circuit and used it to trigger 2 relays...one for each bulb....no real reason other than i had lots of relays and just figured they draw so little milliamps that using 1 circuit to feed 2 relays was just fine

 

i didnt go to the battery for source ...its been a while but i think there was a large constant voltage source right on the outside of the sam unit that i used to grab the main power

 

 

 

the guy came back just a few weeks ago with only one light working and was all worried that the problem returned and expected major sam problems...but since i knew they were controlled by only one feed we just changed out his burnt bulb and he was on his way

Edited by LooseLugNuts

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Anyone have a lead on where to get that replace/repair harness?  I'm in the US, so maybe a bit trickier? unless its a common thing to get from MB down here, or RockAuto, or one of those. But if its an aftermarket source, which one, and what are they calling it (part number or name)?

 

And I see now the many more threads on this topic, so thanks for the replies, which I assume gets a little old ..... 

 

But most say do the relays for the fuel pump and low beams, though someone mentioned the DRL (driving lights?).  If so, I don't see a driving light circuit on the Evilution SAM pin out.  What do those run off of.... meaning what's that circuit called?   (If its the Low beam circuit, that would make sense.)

I do run the driving lights, or "parking lights", all the time, though I'm running little LED's up there so the draw on that end of things is small (wouldn't change the Sam output i suppose).

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DRL utilizes the low beams, if activated.  There are online sources for MB parts in the US.  I would try there first.  Or do a web search for the wire harness part number and see what pops up.

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Posted (edited) · Report post

doubt youll need a harness

 

plug that usually melts is part number Q0015374V001000000

 

 

Edited by LooseLugNuts

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16 minutes ago, LooseLugNuts said:

doubt youll need a harness

 

plug that usually melts is part number Q0015374V001000000

 

 

You mean just clean up the plug that I have?

i took a quick look at it tonight (finally had a chance to get it into garage for a minute after work), and the one low beam pin area does look a little wrong, though not horrible.  Next I'll pull the plug apart, and see it looks for heat damage underneath.  Fuel pump pin area looks normal, at first glance, but will do the mod anyway as suggested.

 

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The plug will be cheaper than the harness.  The latter is $70 unless you get yours for free as I did.  In my case not only the plug was melted but one of the low beam connectors itself (metal) was badly damaged as mentioned in my "How To", so I used two bits of the repair harness too.  You can try cleaning it up if you want.

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Ok.

I just try and avoid the MB dealer (of course), as we share a mutual dislike.....me with my PITA car and them with their pricing, distance, and hassle factor.   I'mnot finding any good leads online for other options for a new plug.  There are a few German web sites that appear to mention it, but that won't be any better than my MB dealer.

I'll see about cleaning up what i have, but will get with the local MB folks and see if i can get that plug coming.  

 

This topic is well beaten up, and thx to all for the quick enlightenment for me.

But while I'm on it, a related question of less importance:  I assume the root of the issue stems from smaller gauge wiring (etc) leading to heat issues, which in turn leads to various symptoms that ultimately cause failure (of the juice to flow).  Common issue in most of my older Italian motorcycles, and upgrading wiring and connectors is usually the fix.  In this case we have the SAM, so we're stuck with certain elements there, assuming someone doens't want to really get in deep.  

But is it true that the output from the SAM is what directly powers the low beams?  We're adding the relays and the fresh (and larger) power supply for the low beams and fuel pump, so that makes sense.  But if an excess of current flowing through such a small gauge wire (and perhaps lower grade wire? And/or connectors...) is the issue, then would converting to LED headlamps with their smaller current draw also be a way to avoid the issue perhaps?  (Too late for many of us either way if the heat damage is already present).  If so, that wouldn't do anything for the fuel pump, but just curious.... either improve the supply side of things, or reduce the draw?

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Possibly LEDs would be better but any bulb without a filament does not work in a car with reflector headlights - hello blinded traffic!

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ive never seen the wire size as a problem...it looks like they just made the pins too small..or maybe bad batch in production ...my friends 450 has burned out the headlight pins and the fuel pump pin while mine which is same year and same mileage still has a connector that looks like it just came off the factory line

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The light "spray" from LED's and some HID's i know is an issue, though my understanding is that there are solutions for that now available... but i haven't dug into it. 

And I'm probably missing something obvious, as it doesnt' sound quite right, but a 55w halogen draws 4.5 amps?  Seems high.  But if thats right, then that x2  low beams, plus the DRL lights (etc), so over 10amps, would seem a heavy continuous load for those wires and especially those pins (as Looselugnuts noted).  I must be missing something easy?

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Posted (edited) · Report post

3 hours ago, GMC28 said:

The light "spray" from LED's and some HID's i know is an issue, though my understanding is that there are solutions for that now available... but i haven't dug into it. 

And I'm probably missing something obvious, as it doesnt' sound quite right, but a 55w halogen draws 4.5 amps?  Seems high.  But if thats right, then that x2  low beams, plus the DRL lights (etc), so over 10amps, would seem a heavy continuous load for those wires and especially those pins (as Looselugnuts noted).  I must be missing something easy?

 

those wires are fine for 5 amps

 

you can feed 2 relays no problem from 1 sam pin...bulb draw is no issue because bulbs will be fed thru relay and external power source....only the added relays are fed by the sam 

 

the relay control circuit is milliamps ...as low as 10 ...or up to 50 milliamp depending on type ...either way its negligible 

 

 

 

use 4 or 5 pin relays...30 goes to battery...87 goes to the bulb wire(or fuel pump wire)...86 goes to sam pin ..and 85 goes to a ground

Edited by LooseLugNuts

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1 hour ago, LooseLugNuts said:

 

those wires are fine for 5 amps

 

you can feed 2 relays no problem from 1 sam pin...bulb draw is no issue because bulbs will be fed thru relay and external power source....only the added relays are fed by the sam 

 

the relay control circuit is milliamps ...as low as 10 ...or up to 50 milliamp depending on type ...either way its negligible 

 

 

 

use 4 or 5 pin relays...30 goes to battery...87 goes to the bulb wire(or fuel pump wire)...86 goes to sam pin ..and 85 goes to a ground

All good there, though thanks in any case.  Am comfortable with the relay use and installs, being a foolish fan of older italian motorbikes, where such "upgrades" are commonly required.  Burnt wiring on several of my older bikes was a common thing, and now I pro-actively upgrade them when i get another one, without waiting for symptoms to show up.

I was just musing about the logic of where the weak spot in the original system is/was, and i agree the pins would be the logical choke point if running 5+ amps through each connection, though the connectors themselves could also be the weak spot.

No question the upgrade you've all done and pointed me to well addresses the issue.  Ordered the plug today from MB down here.  Will come from Germany, so 7-10 days out....

many thanks!   the mighty 3 cylinder still puts a smile on my face.

 

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Thanks for the input/support on this.  All good now.  Or at least so far....

Took a while to get the harness/plug from Germany, and as noted above i'm not convinced I had to have that, but it did make it a better/cleaner repair, especially for the long term.

 

Observation or two to share:

The fuel pump and low beam pins were in fact a bit heat damaged, at least on the plastic part of the plug.  The failed right beam's pin (metal, on the sam) did still put out the 12v, so the SAM is ok.  But I found that the fuel pump wire had been (poorly) previously jumpered to the windshield wiper lead.  Hmm.  I'm assuming perhaps the fuel pump failed on the previous owner, probably due to the heat damage on the plug, so someone jumpered it to get it back on the road, and then just left it that way.  I waffled back and forth and then finally decided, probably not wisely, to leave that jumper in place, but fixed it up for a proper connection.  Couldn't think of a real down side, other than it just seems wrong, and then other than possibly having the connection fail again (unlikely with new relay setups) and not being able to realize that had happened because of the jumper, but am i missing something else as to why that would be bad? 

 

And the whole SAM was just sort of jammed up in there in that under-dash space, not really attached to anything.  Another clue that maybe the jumper was there due to a road side fix, done in somewhat of a hurry in the past by PO.  I re-connected it when all done to the aft (closest to driver) attach points, which I saw tucked up there, but it's just resting oddly on nothing really at the front end, as the brackets up there weren't attached and didn't quite make sense to how they were supposed to be laid out.  hard to explain, but in short the only way i could make sense of how it was supposed to attach up front didn't seem to work. But i'll admit that with a bad shoulder I wasn't super eager to spend more time contorted up in that space.  I'll have to watch that, and maybe take more steps on that...

 

The new, extra relays (low beam and fuel pump) worked slick, and its set up to where it should be reasonably easy to pull it all apart again later if needed for any reason.  I just ended up laying the relays one on top of the other up there, with wires cut to fit, so things didn't really want to move.  Made me slighlty uneasy to not mount the relays, but on the whole felt that the combo of my difficulty contorting myself in that space, plus the fact that those relays would be hard pressed to move from where i have them tucked in with proper wire lengths, let alone be caused to malfunction because of any serious movement, allowed me to justify giving in to the dark side and leave them as is, just tucked in and laying there on top of the sam.

 

In the end its good to have it back on the road.  Getting to wet to ride (comfortably) here in Oregon, and the truck is too thirsty!

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Just a comment about the fuel pump and headlight corrosion problem.

 

A number of years ago I had serious water incursion into my SAM and a number of pins on the connector were also corroded.

 

The speculation at the time is that there was a windshield leak.

 

My feeling is that the problem is in fact due to cold weather or air conditioning  condensation accumulating on the wiring harness and wicking down into the SAM.

 

This problem is likely compounded by having an unvented 12V battery in the passenger footwell.

 

After fixing the SAM and using a contact cleaner on the connectors, I jammed a sponge around the wiring harness just above the SAM.

 

Five years later, parked outdoors in a Canadian climate, no further problems.

Edited by smartdriver

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