Here's a picture of a foot that came with my Viking Quilt Designer 1. I have no idea what it is, or where you would put the "plug." Does anybody know what this is for?

is that a bsr? for free motion? mine looks like that ..the pulg goes kinda where the light bulb that shines down on your needle are..you need to turn upside down to see it lol..or use a lil compact mirror

I'm not sure but it looks like it might be a FM stitch regulator of some kind. It should plug into the machine probably some were in the back, maybe close to the needle area.

BTW, the red thing on the side is a "wheel" with tiny teeth

I just used a friend's Viking the other day and the foot is described in the manual...I think it's for something to be measured like a buttonhole, etc. but can't remember specifically...check your manual

It is a "Sensor One-Step Buttonhole Foot". It works great for making a number of buttonholes exactly the same size.

to compulsivequilter:
The Viking foot you posted a picture of is a special automatic buttonhole foot for the Designer series and other later Viking machines..it's called the Sensor Buttonhole Foot PAGE 49 IN YOUR DESIGNER I USER GUIDE. If you don't have a User Guide, get one. Also, seek help from your Viking dealer. They have owner classes, often free.
Two bits of advice for you:
1. Spend an afternoon with your machine and the User Guide. Read the Guide from cover to cover. If you only do quilting much of the special stuff won't apply to you, but you'll understand the way the machine works better.
2. Get friendly with your dealer and other customers there. If they offer workshops go to them. You'll be surprised what you can learn from them, often critical info. for FREE.
I make a practice of stopping by my local dealer/quiltshop at least every other week. Sometimes I just buy 1/2 yd of a fabric I like. I once attended a free sew session because my granddaughter was there for a beginner sewing class. The instructor only spoke "quilt". I volunteered help to other attendees with questions. Made several new friends and actually got paid for helping.
Too many quilters are snobs. They only know quilting and don't even recognize any other type of sewing. Shame on you. You have no idea what you are missing.

I know a lot of people don't buy their machines from a dealer and here is the reason why I won't buy one from anyone BUT a dealer. My dealer offers "New Owner" classes and teaches the use of every accessory that comes with the machine. They also showcase feet that are not included with the machine but are valueble to the normal sewer. You get a chance to try the feet, do a few samples, write instructions, etc. It is great. We also are entitled to be members of the sewing club and learn new sewing techniques/projects to work on for ourselves or charity organizations. Try finding out if your dealer has a "Fun With Your Feet" class. Those are great. You learn a lot of new techniques and what each foot actually does.

I bought my machine from a dealer but the nearest dealer is a good hour away so I don't have the time to go and take classes. I am still glad I got it there in case of problems, and they will, if needed, instruct me on the machine. But everyone isn't lucky enough to have any dealer close by. :(

I used to live 1 1/2 hours away from mine before I moved. I still went once a month. It was a great way to "go to town" for me. My husband would even go on some of the day trips, drop me off, and go do "guy" things before coming back to pick me up.