Picked up a used 06 Mark LT. So far I jave found 2 electrical problems. Looking for help. I doubt they are related.

1. Horn didnt work. Fuse was blown. Replaced fuse but now they are very very weak and hardly audible. They are not water filled.....

2. Truck seems to run and drive normally. BUT with the headlight switch in the auto position, the truck will not shut off. I can take the keys out and truck stays running. Turn headlight switch to off and truck shuts off. If the headlight switch is in the off position, the truck shuts off like it should.

What kind of aftermarket add on would tie onto this and cause this? Or i it a known factory problem of some sort?

 

Just a thought...... does it have a remote start? If it does will it die if you try to put it in gear with the key out?

 

I don't know if it has remote start or not. I didn't get any fobs for it and there are no warning stickers on it.

With key out I can put foot on brake,shift into drive and go. Keys in pocket. Put it in park, turn off auto headlights and truck shuts down. Wtf

 

Get your head up under the area of the sterring column and look for any add-on boxes. A left-over remote starter accessory is the most likely reason for #2.

As for #1, the horns are the most likely issue, but a miswired or malfunctioning remote start module might explain your symptoms, so check that first.

 

Hard wired the horn direct to 12v and got the dying duck sound...The horns are toast. I will buy a new assy...

#2 has left me with more questions than answers. Someone tied into the violet/orange wire on the back of the headlight switch This wire goes from the switch to this plug, which is plugged into this relay or whatever it is. The black wire off this pigtail is ground out on the knee bolster. The white is only 2 inches long and is taped to the yellow/red wire. I didnt check if it was twisted copper to copper or just taped there with the sheilding still on. Didnt see the point.





The yellow/red wire from the pigtail then is spliced into the blue wire with green stripe in the main steering column harness.First... What is the blue/green wire in the column harness, and what might be the reason someone would do this? I dont really want to undo it until i know why it was done in the first place.

 

Since projectSHO89 got you pointed in the correct direction, I will take a stab at the wire colors.

These are estimates as to what it is, as color codes get reused in the truck. the only way to know for sure is to trace the wire back.
- This is slightly better than a SWAG from the gauge of the wire.

Dark Blue w/ light green stripe could be the output of the ignition switch Start / Run position.

It feeds back to the CJB ( aka Central Junction Box / cab fuse panel ) on connector C270G, circuit 946
In the guts of the CJB, it feeds 2 branches of fuses that are hot in run / start positions.
1 is to Fuse F13, and on to a bus to the coils on relays for the front blower motor, heated rear window and trailer tow battery charge, flashers and EATC ( hvac control panel )

The other to a bus that feeds fuses;
F14 - ABS, Aux rela for DRLs, Ac module, PCV, DTR.
F15 - Instrument cluster, floor shifter, traction control
F16 - brake pedal position switch
F18 - BSM / VSM, heated seats, parking aid, aux power point.
F19 - restraint system
F27 - instrument cluster
F28 - PCM, PATS module
F34 - PCM ( 8 inputs )

My SWAG ( of the most Wild kind ) is this is a hidden ignition switch bypass like police vehicles used to ( still do ? ) have in them, so the vehicle will still run with the keys out.
- It will operate, but the wheel is locked, so it could only drive in one direction.

That is just a guess on my part, I might be wrong about the wire or the purpose.

I would say pull the relay out of the socket and check vehicle operation.

i anticipate it will operate as it should from the factory, and will not continue to run with the key turned off.

 

I think he's onto something there. ^^^^

Your picture most definitely shows a relay. What it looks like is as described above.
The switch in "auto" position continues to provide power to your drivetrain through the relay until you put the light switch in the "off" position.

The Violet (PPL) and orange wire is a power feed to the Auto lamp module I believe.
The Blue/Lt Green wire on the column is the output side of the ign switch

The relay is essentially keeping the power turned on (WHILE THE AUTO-LAMPS is energized) if you unplug the relay I would be confident that your vehicle will work normally no matter what position the headlight switch is in.
Meaning that you can safely remove the added in wiring

 

Decided to keep it. I consider it a poor mans remote start..... And i have already used it to pull the keys out with the wife and kiddos in the truck and let them listen to tunes while i run into the house for something we forgot.