Strange Fog Light Problem

[GreatBu]

OK internets, I have a strange problem with my fog lights:

- 2011 RAM 1500 Sport Hemi
- Right side fog light is not working, left side is fine
- I have tried the bulb from the right in the left side and it works, so not the bulb
- Tested the connector pins on the wiring harness where they connect to the bulb, reading 14v when on (same as the left side)
- Thought it might be a bad connector so I have replaced it anyway, still reading 14v but bulb still not illuminating
- Other bulb from the left side displays same behavior (works on the left, not on the right)
- Fog lights are just the standard OEM H10 bulbs (not LEDs or anything fancy..)

What am I missing ?

 

[Curmudgeon]

I like your trouble shooting. Easy to follow what you've done, and your logic flow seems sound.

And I understand the confusion, bit of a head-scratcher.
One question though. When you tested and found the 14v on the right side, were you at the "back" side of the connector? Or the "bulb" side?

My remote intuition (from waaay over here in York PA!) is a bulb/connector issue, you seem to have ruled out everything else.
I'm also wondering if your meter lead is making a connection that the bulbs are not. Maybe due to the pressure of your hand? Maybe something is "loose" and the bulbs don't light when left hanging but when you're holding stuff to get a voltage reading, suddenly a weak connection becomes good?

Lastly, current. Virtually no current is required for your meter to read the 14v but the bulbs will need all they can get to light up.

 

[GreatBu]

Thanks for the rapid response, the 14v was on the bulb side of the connector and I also replaced the connector itself as I suspected it had to be the bad part but the problem persists. Not sure about the current, how much should the light draw ?

 

[SitKneelBend]

Thanks for the rapid response, the 14v was on the bulb side of the connector and I also replaced the connector itself as I suspected it had to be the bad part but the problem persists. Not sure about the current, how much should the light draw ?

Check the working side for voltage reference. If you have AlfaOBD, you can see what the target voltage is set to.

 

[Curmudgeon]

Thanks for the rapid response, the 14v was on the bulb side of the connector and I also replaced the connector itself as I suspected it had to be the bad part but the problem persists. Not sure about the current, how much should the light draw ?

I don't know the wattage rating of the fogs off-hand, but supposing they are 45 watt bulbs the current draw would be
45w divided by 14v, so about 3 1/4amps.

And an afterthought, you could be looking at rust/corrosion/poor connection anywhere from the bulb up to where the wires for the fogs split from each other, anywhere along the path for the right side fog, not just at the connector.

 

[crash68]

Asking for clarification, are you checking the voltage where the fog light bulb plugs in and are you checking between the terminals that goes to the bulb?
You don't want to check to ground, also you may need to have the ignition on but the engine not running.

 

[Bigskyroadglide]

Almost sounds like some led bulbs that you have to turn over due to the polarity being off. I know you said the bulbs were not led.

 

[RamDiver]

I'm with Curmudgeon, and questioning the ground wire connection.

GreatBu, could you locate a good ground connection, somewhere nearby, connect a wire to it, and carefully touch it to the negative terminal on the light socket?

Ideally, you would install a new temporary test ground under a screw or bolt and then if you had an alligator clip wire that you could carefully connect to the negative side of the socket, this would prove your ground connection is adequate.

Your stock ground is defective if the light illuminates with the test ground wire. This is the most likeliest of expected faults for lighting issues with an older vehicle.

If your light does not illuminate during the test, the positive side is faulty. I suspect the BCM may be feeding the fog lights but others here will confirm if that is correct.

.

 

[GreatBu]

Thanks all for the advice - I am checking the voltage between the 2 terminals that connect directly to the bulb itself.
I might try tomorrow to disconnect the other end of the fog light wiring loom and see if there is any continuity between the 2 terminals - it may be that there is a short somewhere along the line between the two wires and that is diverting most of the current from the bulb......more to follow.

 

[Curmudgeon]

Your truck is only 3 years older than mine, but here goes...

> If there is a short to ground or any fault resulting in excess current, a fuse should pop, likely taking out both lamps, and anything else on that fuse?

> If there is an open, wouldn't the BCM see that as a lamp out and indicate it on the dash or evic display?

It could always be worse. It could be an intermittent issue!

 

[RamDiver]

Thanks all for the advice - I am checking the voltage between the 2 terminals that connect directly to the bulb itself.
I might try tomorrow to disconnect the other end of the fog light wiring loom and see if there is any continuity between the 2 terminals - it may be that there is a short somewhere along the line between the two wires and that is diverting most of the current from the bulb......more to follow.

I am again in agreement with Curmudgeon. Any partial short across the fog light terminals would most likely take out a fuse.

One thing you could try is, measure with an ohm meter from a good chassis ground to the ground terminal on the problem fog light socket, proving the ground connection.

Use the lowest resistance scale on the meter, 200 ohms or less. First test the resistance of the meter leads shorted together and then from chassis ground to the negative terminal on the light socket.

Take note of the resistance with just the test leads, should be no more than a couple of ohms, and then through the socket.

Next, perform the same test on the working side. Is there any difference between the working and non-working side?

If you see a notable difference, this is likely the root of your grief. Chase the ground wire on the problem side and repair the connection.

Don't forget to remove the bulbs before testing.

.

 

[SitKneelBend]

To pile on, I've never checked but I wouldn't assume the fog lights are on the same fuse. I'd check that and I would also check the BCM for any stored codes. The brains in these trucks can sometimes need a reboot to get something working again after it has decided to shut it off.

 

[GreatBu]

Mystery solved !

Thanks to all for the advice, it turns out that there are 2 output pins from the TIPM (one for each side fog light), I pulled off the relevant connector (as you stand at the front of the truck with the TIPM pulled up out of it's housing, it is one of the ones that connects horizontally (i.e. not into the bottom of the TIPM but onto the flat bit that sticks down at the back of the unit) - it is the only one that is oval in shape, with 2 rows of 8 pins if you are looking for it), cleaned the pins and re-seated it firmly now both lights work.

 

[Marshall]

I would be checking out the ground, where ever that is on these, I don't have a wiring diagram for these.
Back in the old ones, usually grounded throu the rusted socket and wires pulled off with mud.
But if its a single bulb with 2 terminals, then one is ground, check that one with a ohm meter to ground , make sure not to hit the 12v or you can fry the meter, some will have a fuse.

 

[RamDiver]

I would be checking out the ground, where ever that is on these, I don't have a wiring diagram for these.
Back in the old ones, usually grounded throu the rusted socket and wires pulled off with mud.
But if its a single bulb with 2 terminals, then one is ground, check that one with a ohm meter to ground , make sure not to hit the 12v or you can fry the meter, some will have a fuse.

Mystery solved !

^^^^^^^^^^^

Thanks to all for the advice, it turns out that there are 2 output pins from the TIPM (one for each side fog light), I pulled off the relevant connector (as you stand at the front of the truck with the TIPM pulled up out of it's housing, it is one of the ones that connects horizontally (i.e. not into the bottom of the TIPM but onto the flat bit that sticks down at the back of the unit) - it is the only one that is oval in shape, with 2 rows of 8 pins if you are looking for it), cleaned the pins and re-seated it firmly now both lights work.

 

[js12278]

Appreciate you coming back with your findings and a fix. Glad you got it resolved. Nothing worse than never knowing, good or bad.

 

[SitKneelBend]

Appreciate you coming back with your findings and a fix. Glad you got it resolved. Nothing worse than never knowing, good or bad.

Agreed! So many open threads out there...

 

[Hardracer]

My guess was leaning towards the Tipm by what you describe as I had the same symptoms on my right front head light. bulb was bad, put new 1 in,about a week later no light,bulb good,swapped sides as you did,pulled the pigtail connector apart,actually melted inside where connection is made,started doing the meter thing...unfortunately for me my Tipm could not be fixed,dealer confirmed all i did with the same results.the guy was(seemed)pretty good and persistent,sent me video of everything(actually impressed on that part)explained how it all worked..it was a ground issue and was fried in the Tipm..drove me nutz for awhile.