Fox T-Bird/Cougar Forums

Technical => Electrical Tech => Topic started by: V8Demon on January 29, 2020, 02:50:57 PM

Title: Lamp out/Flash to pass issue
Post by: V8Demon on January 29, 2020, 02:50:57 PM
Got a weird issue that popped up almost 2 months ago.....

--Parking lights on causes lamp out light to come on
--Headlights on causes lamp out light to come on
--With no parking lights/headlights on stepping on the brake pedal lamp out light to come on
--With no parking lights/headlights on using the turn signal will cause the lamp out light to come on and then go out with every illumination of the turn signal. 
--With no parking lights/headlights on pulling the hazard light switch will cause the lamp out light to come on and then go out with every illumination of the hazard lights. 

The flash to pass function has also stopped working.  This occurred at the same time If I hold the turn signal stalk back the brights will stay illuminated. 

I'll preface this with the fact that I did an ENTIRE LED bulb swap on the car and there were no issues for MONTHS.  I swapped over to LED in October/November of 2018.

Today I swapped out the turn signal switch only to find the one I received is apparently bad because the brights are stuck on no matter what I do.  I swapped the old switch back in for now.  I know there's a circuit breaker in the fuse panel for the flash to pass function, but it also correlates to the horn which works.  Ignition switch is approximately 2 years old and looks good and doesn't get warm or anything like that....

Thoughts?
Title: Re: Lamp out/Flash to pass issue
Post by: mcb82gt on January 30, 2020, 08:59:02 AM
I would start by replacing all  the rear led bulbs with your old regular ones, hopefully you kept them.  Just to troubleshoot.

Good luck.  I hate stuff like that.
Title: Re: Lamp out/Flash to pass issue
Post by: EricCoolCats on January 30, 2020, 10:15:22 AM
IIRC the System Sentry is reliant upon all the bulbs being halogen. Otherwise, a non-halogen bulb will cause the System Sentry to go a little haywire just like you're experiencing now. There must be some resistor wire-y stuff going on.

So it seems like you'd need to put some inline resistors in. They're sold primarily for newer cars; older cars like ours technically shouldn't need them but in the case of System Sentry, I'm betting that's going to help, at least with high-priority bulbs like the headlamps and taillamps. For the rest of the car's bulbs, I think there's just too small of a draw to justify any resistors on those circuits. Just my thoughts on this.

It's been a few years for my LED conversion in both cars and they're just fine...then again, I don't have System Sentry in either car. But no issues with the multifunction switch if that helps.

Speaking of, if you resolve the issue with the headlamps and taillamps, your multifunction switch might just prove to be alright. Sounds like you're getting feedback through the switch...which kind of makes sense with the headlight wiring routing.
Title: Re: Lamp out/Flash to pass issue
Post by: V8Demon on January 30, 2020, 05:32:19 PM
I had someone tell me that perhaps one of the diodes got weak in one of the LEDs.  He also suggested swapping one at a time to see which and also suggested starting with the rear.


As far as the hi-beam issue; I'm a gigantic idiot.  I was digging through my copy of the 87 shop manuals last night.  Came across a diagram that showed how the autolamp/autodim tie into the headlamps.  After that I went to the car to make sure they were both in the off position. 


Suffice to say my original multifunction switch is fine and the hi-beams are working. I did however find an NOS one for sale at a local dealer on their parts website.  I ordered it to add to the "box of many Cougar parts"

The aftermarket switch is in fact bad according to the shop manual tests.  Guess I'll be returning that.
Title: Re: Lamp out/Flash to pass issue
Post by: EricCoolCats on January 31, 2020, 09:32:18 AM
Ahhh, okay, the auto lamp/dim thing makes sense then. Glad you figured that out, that would drive a person nuts LOL.

So with those out of the picture now, you're still getting a 'lamp out' warning light? That person might be on to something...personally I haven't experienced a bad LED bulb but that's entirely possible.

Another thing you can try is swapping in the old incandescent bulbs, one at a time, until the warning light goes out. That should give you an idea of which LED bulb has the weak diode. I've found that, once swapped to LEDs, you can put the old incandescent bulbs back in without penalty to the new LED-spec flasher unit. (You can actually mix bulbs and everything still works just fine).
Title: Re: Lamp out/Flash to pass issue
Post by: V8Demon on January 31, 2020, 12:50:59 PM
I know.  I did the bulbs over the course of a few days and had a hodge-podge of incandescent and LED going on when I was doing it.
Title: Re: Lamp out/Flash to pass issue
Post by: softtouch on January 31, 2020, 07:19:31 PM
I am guessing you have one lamp out warning light.
With system sentry feature you would have three lamp out warning lights. Low beam, brake light and parking light.
The lamp out feature works by measuring the current draw of the bulbs. It does this by sampling the voltage drop across a resistance wire.
For instance, if the Lamp  Out Module senses a 0.5 voltage drop when powering two bulbs, the sensed voltage will drop to 0.25 volts when one bulb burns out. 87 EVTM page 120
These resistance wires are calibrated to work with the stock bulbs.
If you are a trouble shooting type, you could measure the sense voltages at the Lamp Out Warning Module.

I think you should have had the warning light from day one. Maybe the warning light bulb socket has gotten crusty over the years and just starting working again.
Title: Re: Lamp out/Flash to pass issue
Post by: softtouch on February 01, 2020, 08:18:24 PM
To measure the sense voltages at the Lamp Out Module, put a meter lead at each end of the resistance wire.
Title: Re: Lamp out/Flash to pass issue
Post by: V8Demon on February 05, 2020, 01:10:59 AM
Quote
I am guessing you have one lamp out warning light.

Correct

Quote
I think you should have had the warning light from day one.

When the issue popped up about a year after the swap, I had the same thought.

Quote
Maybe the warning light bulb socket has gotten crusty over the years and just starting working again.

The bulb rests in a twist lock which inserts into the bottom left on the full digital cluster.  Looking at the tabs on the twist lock it appears and FEELS as if there's more play in that particular one than the others on the cluster.  Perhaps it just fully seated after a bump.  I have other spares in better shape. 

Now that you mention it, there were times where before the swap I have had a bulb out and the indicator DID NOT light up.
Title: Re: Lamp out/Flash to pass issue
Post by: softtouch on February 05, 2020, 02:11:57 PM
Do you still have a flash to pass problem?
In addition to fuse 10 that powers the Hi beams and the horn relay, there is fuse18 that powers the Flash to Pass relay coil.
Title: Re: Lamp out/Flash to pass issue
Post by: V8Demon on February 06, 2020, 11:02:18 AM
No, that's been rectified. 
Title: Re: Lamp out/Flash to pass issue
Post by: EricCoolCats on February 06, 2020, 01:52:28 PM
So softtouch...what I'm gathering from all this is that the resistor wiring for the System Sentry/lamp out system seems to also be calibrated with just enough tolerance for LED bulbs as well as the factory incandescent bulbs. Does that sound reasonable?

I did the LED conversion on my own two cars but neither had the System Sentry. If there's a problem then I need to let people know about that on my site. But it sounds like, if all else is working properly, then the LED conversion is still not an issue.
Title: Re: Lamp out/Flash to pass issue
Post by: softtouch on February 07, 2020, 01:06:45 PM
So softtouch...what I'm gathering from all this is that the resistor wiring for the System Sentry/lamp out system seems to also be calibrated with just enough tolerance for LED bulbs as well as the factory incandescent bulbs. Does that sound reasonable?
I think the warning light should have come on when put the LEDS in the tail and brake lights. That's why I suggested something may be flaky with the warning light. It healed itself.
One of the benefits of LEDs is they draw less current for the same amount of light.
I suppose the LEDs could be designed to draw the same current as stock bulbs to be compatible with the Lamp Out feature.
I would expect that to be mentioned in their specs if that were the case.

Maybe V8Demon would be up for measuring the sense voltage at the module. Compare the LED and stock voltages.
½ volt= good bulbs. Less gets into the bad bulb range.
Title: Re: Lamp out/Flash to pass issue
Post by: Haystack on February 08, 2020, 02:59:16 AM
I used to use 1156 bulbs to discharge model airplane batteries. They pulled 12 watts (1 amp) each.

I dont think that a voltage drop would be very accurate, but I can't say I've researched it much. Also when measuring voltage on two different cars tail lights (my 86 cougar and 87 tbird) they were 9v at idle with the headlights on. There is pretty significant voltage drop.
Title: Re: Lamp out/Flash to pass issue
Post by: V8Demon on February 10, 2020, 12:49:51 AM
I'd be up for measuring the voltage.  I gotta pull the cluster again anyway (magically my parking brake light has decided to tell me it hates me by THAT bulb going out....)so I'll be playing dash bezel commando again.  May as well....


Title: Re: Lamp out/Flash to pass issue
Post by: softtouch on February 10, 2020, 07:55:40 PM
The EVTM shows the module above the glove compartment.
You can unplug the two connectors from the module to make the voltage checks.
I couldn't find any connector pin numbers, so you will have go by the wire colors.
You will need to put the + meter lead on a wire in one harness connector and the  - meter lead on a wire in the other connector.  I know that sounds like you will need three hands .
Title: Re: Lamp out/Flash to pass issue
Post by: V8Demon on February 12, 2020, 08:22:34 PM
I know that sounds like you will need three hands .

What with all the other interior stuff that's been popping up on this car, I need 7.

New front windshield on Friday.  I've been fighting (and losing) to a small leak during heavy rains.  It's time to pull the glass.  I noticed some delamination around the top edge. May as well replace it.  Already took all the trim off along with the wiper arms, cleaned up the upper channel, and have all new clips ready to go.  After that I get to reskin the headliner.  The new sun visors I want to use have a smaller mount footprint. 

22 years of owning this car.  I think over that time It's ran great and looked great at the same time for about 4 of them.  It's usually one or the other.  It's never run better than right now.  Figure out how it looks.....