Fox T-Bird/Cougar Forums

Technical => Electrical Tech => Topic started by: FOX-XR7 on April 03, 2015, 01:48:53 PM

Title: Tail lamp fuse
Post by: FOX-XR7 on April 03, 2015, 01:48:53 PM
I noticed I don't have tail lamps when I turn my marker lamps on. I pulled the fuse and it was blown. So I put another 10 amp fuse in and it popped as soon as I hit the light the marker lights. My best guess is would it be a short to ground? Can anyone give ideas what it may be? Thanks for the help.
Title: Tail lamp fuse
Post by: CoogarXR on April 03, 2015, 03:28:30 PM
If you've been working under the dash, you might have pinched a wire. I know one time I dropped the steering column in my mustang and pinched one of the lighting wires in the bracket when I put it back up. Shorted, smoked, scared me to death, thought my car was on fire, etc. Good times.
Title: Tail lamp fuse
Post by: FOX-XR7 on April 03, 2015, 04:48:55 PM
That could be exactly what happened. I was messing under the dash alot. I'll have to follow the wires. Thanks CoogerXR
Title: Tail lamp fuse
Post by: Trinom on April 05, 2015, 03:07:39 PM
Follow brown wires :)
Title: Tail lamp fuse
Post by: FOX-XR7 on April 06, 2015, 03:47:09 PM
Brown. Got it. Thanks Trinom
Title: Tail lamp fuse
Post by: FOX-XR7 on April 15, 2015, 08:21:59 PM
X
So while using this schematic as a guide, I turn on my parking lights, and I have them up front, along with marker lights. The tail lights however are alll out. When I put a new fuse in and it blows as soon as it turns on, it tells me that it is short to ground on the brown wire. But because only the tail lights don't work, does that mean that the short is between the fuse and the tail lights? Or could the short be between the fuse and the light switch? I thought if it was the latter, then no lights would work. Am I correct?
Title: Tail lamp fuse
Post by: softtouch on April 16, 2015, 01:50:59 AM
Yes, the short is below fuse 15 in the diagram.
That also includes the lamp-out warning module as well as the bulbs.
Title: Tail lamp fuse
Post by: FOX-XR7 on April 16, 2015, 08:03:47 AM
Oh alright. That is great info. I was unaware of that since it doesn't appear that way on the diagram.
Title: Tail lamp fuse
Post by: kendoo130 on April 16, 2015, 08:43:33 AM
Also check the light blue w/ red stripe wires under the dash and behind the radio. These are the dash illum + wires. They show ground when the lights are turned off causing them to be used as ground when hooking up accessories like gauges or radios. I install car audio and see this mistake quite often. This will also cause the tail lamp fuse to blow in most cases.
Title: Tail lamp fuse
Post by: FOX-XR7 on May 17, 2015, 10:01:57 PM
Here's a random thought....some guys at work said it could be my tailights bulbs themselves? That they may be grounded through the bulb? And if I bulb shorted, that could be blowing the fuse. Is this myth? Or could this be possible?
Title: Tail lamp fuse
Post by: Haystack on May 18, 2015, 03:21:05 PM
I've never seen it on any of my cars, bit it is possible.

Do this first.

You have both illumination and brake light signal wires for power. To blow a fuse, it pretty much has to be grounded out. Check for negative on your tail lights first. If you have a ground, you know both which wire it is, and that it is somehow directly shorted out
Title: Tail lamp fuse
Post by: FOX-XR7 on May 18, 2015, 03:48:57 PM
Quote from: Haystack;448135
Check for negative on your tail lights first.

I'm sorry to be ignorant, but I'm a bit cloudy with how to go about checking for negative on the tail lights. Please inform me on how to do this. Sorry again
Title: Tail lamp fuse
Post by: TurboCoupe50 on May 18, 2015, 05:33:47 PM
Quote from: FOX-XR7;448122
Here's a random thought....some guys at work said it could be my tailights bulbs themselves? That they may be grounded through the bulb? And if I bulb shorted, that could be blowing the fuse. Is this myth? Or could this be possible?

Probably more myth than reality... Easy to test, remove all the bulbs on the supply side of F15(to the south of fuse), if fuse still blows, that ain't the problem...

If signal & brake lights are normal, not likely a problem with the tail lamp bulbs, though I have seen a busted bulb cause a short(start checking side marker, license, etc bulbs)...

My bet is there is a pinched brown wire somewhere between fuse and tail lamps...

BTW assuming you have the feature, there is a possibility of a issue with the lamp out module...
Title: Tail lamp fuse
Post by: TurboCoupe50 on May 18, 2015, 06:57:30 PM
Quote from: Haystack;448135
Check for negative on your tail lights first. If you have a ground, you know both which wire it is, and that it is somehow directly shorted out

Huh?? Ground supplied to bulbs is same as a connection to body/chassis, if it shorts to body no foul, no harm... If ground were shorted to supply(brown wire, or a internal short in bulb), it's still same as supply wire shorting out to ground...

If ground were missing the lights would not burn but would not blow the fuse... I had this problem with backup lights on the '95 LX, ground wire to sockets was broken at trunk hinge...
Title: Tail lamp fuse
Post by: Haystack on May 18, 2015, 09:00:52 PM
Sorry, i didn't describe that properly.

Grab your volt meter and check your positive wires at the tail light, and look for a ground on the positive wires. You have the illumination lights, turn signal or brake wire that could be shorted out.

You can either do a resistive test from a good know ground, or find a power wire that works and see if you have voltage, looking for ground on a positive wire. That way you can at least rule out the other wires, and measure different parts of the car to see where the fault is. Worst case scenario, you figure out which wire is bad and run a new wire to replace it.
Title: Tail lamp fuse
Post by: FOX-XR7 on May 18, 2015, 10:05:37 PM
Ok. Now I'm better understanding how I can do this. Thanks for the help guys. I'll let you know what I find.
Title: Tail lamp fuse
Post by: FOX-XR7 on May 20, 2015, 03:07:16 PM
So I've torn the dash back out, I've tested the brake lights, and turn signals. They all work. I pulled out the 4 bulbs for the two rear markers, and the lic. Plate lights, tested each bulb. Good to go. I've searched the light blue and red striped wire behind the dash. No breaks other than a bad bulb for the headlight switch bezel. I'm wondering if the coach lamps could be bad and causing the fuse to blow when the switch is moved to parking lamps. Are they on the same circuit? I'm about to check the brown wires again, just wondered if the electroilluminescent lamps could be at fault. Thoughts?
Title: Tail lamp fuse
Post by: TurboCoupe50 on May 22, 2015, 10:30:26 PM
Quote from: FOX-XR7;448194
So I've torn the dash back out, I've tested the brake lights, and turn signals. They all work. I pulled out the 4 bulbs for the two rear markers, and the lic. Plate lights, tested each bulb. Good to go. I've searched the light blue and red striped wire behind the dash. No breaks other than a bad bulb for the headlight switch bezel. I'm wondering if the coach lamps could be bad and causing the fuse to blow when the switch is moved to parking lamps. Are they on the same circuit? I'm about to check the brown wires again, just wondered if the electroilluminescent lamps could be at fault. Thoughts?


You are wasting you time checking anything that isn't below F15 on on that wiring diagram...
Title: Tail lamp fuse
Post by: Trinom on May 23, 2015, 02:03:25 PM
Quote from: FOX-XR7;448194
I'm wondering if the coach lamps could be bad and causing the fuse to blow when the switch is moved to parking lamps. Are they on the same circuit? I'm about to check the brown wires again, just wondered if the electroilluminescent lamps could be at fault. Thoughts?
Yup, they are connected to parking lamps too, as well as lamp out warning module (if you have one).
Title: Tail lamp fuse
Post by: FOX-XR7 on May 30, 2015, 06:10:42 PM
So I've pulled all the bulbs out of the trunk and I jumped the blown fuse with my test light and it lit up. So that tells me there is still a short to ground other than the bulbs. I pulled the harness up from beside the door jam and found nothing wrong with the wire. I guess my next step is I want to check the sockets in the trunk 5o see if they could be shorted. I neglected to check them the first time I had the bulbs out. Then if they all check out. I'll try and access the wiring from the door jam to the trunk it runs along the back seat it looks like. Also looks like a royal pain. But I already got the car torn apart so what's a backseat right? I'll keep you guys posted as to what I find.
Title: Tail lamp fuse
Post by: TheFoeYouKnow on May 30, 2015, 11:56:17 PM
Quote from: FOX-XR7;448122
Here's a random thought....some guys at work said it could be my tailights bulbs themselves? That they may be grounded through the bulb? And if I bulb shorted, that could be blowing the fuse. Is this myth? Or could this be possible?
I actually saw this once on a pickup.  The filament was offset somehow, and when the truck would go over a bump it would jump contact from tail power to brake ground IN THE BULB, and blow the fuse.  I should have kept it, people usually don't believe me.
Title: Tail lamp fuse
Post by: FOX-XR7 on May 31, 2015, 03:20:41 PM
Well I cut apart the line from the fuse to wear it connects to the rear taillight wires. I then pulled all the bulbs out and one by one, connected the turn/brake/marker lamp brown wires to the main brown wire from the fuse. Meanwhile I have my test light across the blown fuse with the power on. The test light never lit. As soon as I installed a lightbulb, the test light lit. Now is it only doing this because the bulb is completing the circuit to ground? I'm thoroughly confused now as to why this  fuse keeps blowing. I don't understand what I'm doing wrong.
Title: Tail lamp fuse
Post by: TurboCoupe50 on May 31, 2015, 03:42:15 PM
Quote from: FOX-XR7;448491
Well I cut apart the line from the fuse to wear it connects to the rear taillight wires. I then pulled all the bulbs out and one by one, connected the turn/brake/marker lamp brown wires to the main brown wire from the fuse. Meanwhile I have my test light across the blown fuse with the power on. The test light never lit. As soon as I installed a lightbulb, the test light lit. Now is it only doing this because the bulb is completing the circuit to ground? I'm thoroughly confused now as to why this  fuse keeps blowing. I don't understand what I'm doing wrong.

Yes... If this is a LED test light any resemblance of a short or bulb installed will light the test light... A test light with a 194 bulb or similar will light dimly with only a side marker installed and go to full bright with a couple installed...

Good news is there is no short and it appears the fuse is undersized... Install a 15 amp fuse and try it... If it blows well something is up, if not you're golden...

Note I believe I saw the models without system sentry used a 15A IF that's the case models with sentry should have at least as much rating...
Title: Tail lamp fuse
Post by: FOX-XR7 on May 31, 2015, 04:57:31 PM
Yeah Its definitely a red 15 amp fuse in it that keeps blowing. (I've toasted like 6 lol) I guess something is still jacked up with this thing.
Title: Tail lamp fuse
Post by: TurboCoupe50 on May 31, 2015, 06:41:16 PM
Quote from: FOX-XR7;448496
Yeah Its definitely a red 15 amp fuse in it that keeps blowing. (I've toasted like 6 lol) I guess something is still jacked up with this thing.
If it blows fuse with wiring to rear of car disconnected problem has to be between fuse panel and system sentry module(it mounts over glove box opening inside dash)...

Red fuses are 10A, BLUE are 15..

(http://i.ebayimg.com/00/$(KGrHqQOKjYE3R-LyrDrBN-esb)mQQ~~_1.JPG)
Title: Tail lamp fuse
Post by: FOX-XR7 on May 31, 2015, 08:28:03 PM
Quote from: TurboCoupe50;448499
If it blows fuse with wiring to rear of car disconnected problem has to be between fuse panel and system sentry module(it mounts over glove box opening inside dash)...

Red fuses are 10A, BLUE are 15..

Right. Sorry my mistake. I have been putting 10 amp fuses in. I know it's fuse #15.
Is the system sentry module the box where the brn and WHT wires go to lamp out warning module? Is it the same thing?
So the switch is not likely the culprit? Or could that be as well?
Title: Tail lamp fuse
Post by: TurboCoupe50 on May 31, 2015, 11:49:50 PM
Quote from: TurboCoupe50;448260
You are wasting you time checking anything that isn't below(fed by) F15 on on that wiring diagram...


This. ^^^^
Title: Tail lamp fuse
Post by: FOX-XR7 on June 01, 2015, 12:08:58 PM
Well, checked for continuity from power wire in trunk up to removed fuse. I got o.l. Which is good. So there is no short to ground in that wire. I took all bulbs out and threw in a 10amp fuse out of an old wiring harness. Switch on, it didn't blow the fuse. So I put all bulbs back in and wah laa, I got lights. Figured I'd see if this other 10 amp blew then I'd throw in a 15 to try. Now the only thing I did different this time was I used a fuse from a factory wiring harness (spare I have here) instead of tractor supply Chinese value pack. Could those other "value fuses" (if you will) be slightly underrated? Which may answer why they kept blowing? I don't know what I did, but it seems to work fine now.
Title: Tail lamp fuse
Post by: TurboCoupe50 on June 02, 2015, 08:27:39 PM
The ole puppiesinese fuse syndrome huh??

That's why I suggested a 15 amp(that never happened)... After you said the test light didn't light when the bulbs were removed I knew you were chasing a imaginary problem...
Title: Tail lamp fuse
Post by: Haystack on June 02, 2015, 08:43:49 PM
I was doing some working in Montana, 1600 miles away from home. I accidentally left my headlights on when we pulled up to a bar to celebrate finishing the job and getting ready to leave for home the next day. When i went to jump the car, the jumper cables were mis marked (two red clamps on one side) and didn't realize it

It was a balmy 12 degrees with high winds and snow so i sat in the trunk as i reverse charged my battery and blew every fuseable link and fuse.