My fog lights stay on constantly until I turn on the left turn signal at which point the fog lights turn off. I think there is a short in the column

I agree that there is a short.
what could have caused the short?
Has the truck been in an accident?
did you remove the dashboard?
or any other 'under the dash or in the steering column' work?

IMHO, i don't think the cat conv had anything to do with it; the cat is on exhaust mid-vehicle and wiring for items mentioned are in steering column and dashboard where light switch is located.
Unless the mechanics that did the cat work somehow damaged the steering column / ignition switch that may have caused a short... but that is a stretch.
I have not had to deconstruct my steering column or have to deal with the turn signal, so not sure if you have to pull the wheel off first to get at them or not. But if you do, study up on removal process or else you can 'activate' the air bag.

Since I do all my own repairs, this is how I'd go about figuring it out.
Call 5-star dealers until I find someone willing to have a conversation about my problem... find the know it all guy that has answers for everything that 'enjoys a challenge' like this. Don't limit your calls to local dealers... I have found guys that help me that are 3 states away!!!
Let him know that your a DIYer and need info. A lot of times they are willing if they have time. Don't call on Sat at 8 am during weekend service rush.
Ask lots of questions.
Have you ever seen this problem before? What do you think may cause this? Does this sound like a wiring short?
And you most likely will hear 'well i can't diagnose over the phone...'
So I always let them off the hook with 'I agree and not gonna hold you to anything said here, I'm just needing an expert opinion to brainstorm with'. works every time. Continue with questions.
Do i have to take wheel off to get to signal mechanism and or ignition switch?
Ask for stuff !!!!
Do you have diagrams available that I can get/download? Is there a website for exploded diagrams or wiring diagrams?
where can I get copies from a tech manual?

Once you get a lead, try his/her suggestions.
Since this is electrical will mean trying to find the short so you need the equipment and know-how to do that. Use internet if you don't know how to find a short..... Many youtube vids on this and other topics.

before you start taking things apart, do the easy stuff first.
Is the ignition switch damaged? do you have a 'key cluster' of weight that hangs on ignition?? had difficulty turning ignition or inserting/removing key form ignition? Do you start/stop via key hundreds of times a day? could the ignition switch be worn out !?!?!?

are you good at reading wiring diagrams?
Follow the wires that are causing the problems...
signal, headlights and ignition switch.
Look for the obvious first. Broken, pinched, partially cut wires, exposed wires contacting ground....
I wouldn't think that fuses could cause this problem,but check to see if all are ok.
Then I would try eliminating all problems by removing the fuse for the headlight and turn signals.
with fuses removed, start/stop with key switch with light on/off.
if successful, put in signal fuse.
start/stop again.
if successful, or not, try left signal.
remove signal fuse, put in headlight fuse.
start/stop with light on and off.
Does it continue to run until lights turned off?
use the left signal even if signal fuse is removed...
Try all different combos here, it may give a clue to the culprit.

Hmmmmm. Looking back, I think i would try to do as much investigation as possible (fuse check, wiring check and the 'fuse tests') prior to calling svc mgrs... it will give you some knowledge of what your dealing with so you can have an 'intelligent' conversation.

hope this may help somehow. Just kinda ramblin I know, but I can't diagnose it over the pho... internet. ;^)

On the other hand, you have the 'no fix' option.
You could just continue on with an 'interesting vehicle'.
Just make sure there are no police cars around when you don't use the left blinker. Or just take 3 rights.
And look on the bright side... with the weird light switch, you'd never have to worry about leaving your lights on!!!

First check around all the lights (front, rear, headlight, turn signal, parking, fog, etc..) for loose, broken, or bare wires, and/or loose , broken, or bad connectors. Any of these could cause the lighting to short. If everything is in good working order, then the problem will most likely lie with switch inside the column (the lever).

the on/off feature of your turn signals are locatd in th steering column. when the turn signal operates faster than normal it means theres a light out on that particular side.

There is switch at brake pedal under the dash. Might check to see if it is working or disconnected.

Go search in your car forum at

www.mbworld.org

If it is a double filament bulb, try to rotate by 180 degrees in base, since there is a difference in power and touch of the bottom pins

.. Hi there.
This is a typical earth problem. Some of the lights use the same earth and when some of the earth points are not good, the power go through the other lights. That is why some lights go's faster, it's all about resistants. Check all the earth points in the light holders and under the dash and also between the battery, engine and body. Good luck.

Try pushing the Hazard switch on the Column several times and see if it restores the connection. From what I understand about the Multifunction Turn switch is that some of the contacts share connections with the Hazard Button.

The contacts work on a type of derailer setup and when the contacts get dirty or wear, things stop working. Moving the Hazard switch resets the points and springs each time you go in and out of the Hazard setting.

If your brake light is working you know the wires to the light socket from the brake switch are okay. Probably would not hurt to check brake light switch as it shares the common wire. The split between the left turn and right turn signal wire has to occur, yet the opposite brake light will stay on steady while the other side blinks.

Check your steering column. There is a switch that cancels the turn signals in there. If it's bad, your signals will act funny and this also affects the hazard switch. Banging on the dash is what triggers the signals to work as the vibration goes into the steering column also. You might also want to check the fuses, relay switch, located inside the the left fender next to the steering column. Sometimes, the radio and the turn signals will go funky at the same time. Make sure your radio is grounded.
Hope this helps.
Cheryl
1990 Dodge Daytona 2.5 ltr. Automatic

Replace the bulb that stays on and doesn't blink, if that doesn't solve the problem, let me know.