WTF, mate?

[2004-Stroker]

Last night I was fixing my fuse panel cover in my dash and noticed a lone toggle switch tucked up in there. So before I left for work today, I started her and flipped the switch. As soon as I did this, idle dropped to 500rpm and seemed to run a little rough. I flipped it back for fear of unleashing appocolypse on my new truck. Then on my way into work, it was pouring white/bluish smoke out of the exhaust like it was going out of style...

I floored in on the entrance ramp, no power-loss, and it cleared most of it out. One mile and it was all gone. My mpg is still 17.8 and I feel no power-loss and it runs smooth, also no lights on the dash.

I had previous problems with smoke, but I used Howes conditioner and it took that away.

Any ideas on that switch? Don't know if this matters, but my truck is stock (as far as I kow) and will blow black smoke at even a medium take-off. I have reading on "smoke switches", but I don't have powerloss or economy loss.

Also, I just looked and I am low on coolant, as in none in my upper tank that I can see... EGR cooler?

Truck: 2004 F-250 6.0PS w/ 118k on it.

Thanks!!!!

[2004-Stroker]

Update:
I just got done tooling around with the truck. I flipped the switch again, it dropped idle and went right back to where it was. When I would give it a "generous" amount of throttle it just didn't feel like it had the power it had when the switch was the other way. It did not give of any black smoke until I put it under a large load and even then it was a little poof. Could this be some sort of switch for a previous economy tune? Or was the switch for added extra fuel for some more towing power? When I flip it, it seems like it cuts the fuel and the computer just bounces back. I wish I had an EGT gauge... I wish I would have never found this switch so I wouldn't be so curious about this...

[semmens21]

maybe its a smoke switch

[dereku]

follow wires

[nvme_63]

follow the wires if they go to the vgt on the turbo then it is a smoke switch. Not trying to be a Butthead in any way but everynow and then ppl post questions on here about switchs they find in there trucks. witch is fine but we cant tell you where the wires are running you need to trace them and if you find a box or something that they go to post a picture of it and we can help other than that your guess is just as good as mine.

[2004-Stroker]

I know you guys won't magically know what my switch is for. That's why I gave specific symptoms of how its acting to see if it's some sort of common mod or if you all may know what would cause these symptoms. I am totally new to diesels... I wasn't expecting you to know exactly what it was. Just ideas on possibilities. Thanks for all the info though!!!

[107stroker]

trace the wires yet

[Shockley6.0]

tuned in.....

[2004-Stroker]

Ok, more update...
I traced the wires and looked at the switch more. It is a three way toggle switch: here is a diagram that will to the best of my ability, illustrate it...; \ | /. Know what I mean?

There are three wires coming from the switch, two splice into one and ground to the cab. The last one goes through the fire wall and to the (pardon my technical terms) thingy with all the wires going to it on the driver side fender behind the battery. It goes the wires under the middle cover. It is spliced into a blue wire. Pictures to follow....

Now, any ideas on WTF this is??? THANK YOU!!!

[Powerage]

It is putting a ground signal to the computer for some reason. Don't know what the blue wire on the computer is though. What pin number is the blue wire in on the connector?