I recently came by a quilt that is past the point of dirty and really, really needs to be washed. I would like to try to save it if possible but I do not know if it has ever been washed before. I think it may have colors that fade. It is my undestanding that I can wash it in vinigar and it will set the colors and keep them from running. Will this also set the filth? Do I wash it in vinigar before I wash it with Woolight or something made for delicate fabric or do I wash it using both vingar and Woolite at the same time? How much vinigar would I use? Or, is there a product that would work better than vinagar. Thank you for your help.

Just put in a washing machine with cold water and regular detergent, set on GENTLE cycle. It's the best you can do under the circumstances. Colors don't really run much at all in cold...and the dirt will come out.

If you think it has never been washed before I would, for sure, throw a couple of color catchers in with it. I don't have any experience with old quilts or dirty quilts. I wash new quilts in cold water, mild soap, and two color catchers.

I might consider using something called Synthrapol. When I had dye fabric I use this because:
"Synthrapol as the afterwash keeps loose dye particles of dye in suspension so they don't stain other areas of the fabric. This helps white and lighter colored areas from being stained in the final wash by the excess dye. Use 1/4 cup (2 oz) of Synthrapol per full washing machine load for cotton."
After I washed it in synthrapol, then I'd do the regular soap routine.

I like the idea of the color catchers - do they work well?

I use vinegar all the time to help with fabric setness. That is what my mother taught me to do although I have heard that it doesn't do much with dyes these days.

I use a quarter-ish of a cup with my front loader and used a half-ish cup with my top loader. I put it in right with my detergent. When using the top loader, I put the water and vinegar in and let it swish a bit before putting the fabric in. With my front loader I just put it in the dispenser. I alway put vinegar in with any red or black load or towel load since it will also cut musty smell of used towels, allowed to sit damp.

I have never found it to set filth, just colour and rid smells. I also only use cold water. The vinegar also (my mother told me) helped to cut down on suds some and make soap easier to rinse out. Great with something like a quilt that is so heavy and dense when wetl but that you really want to get all the soap out of. I always use the extra rinse setting for a quilt and then air dry.

Ditto

Whatever you do, use plenty of water while washing it.

Don't let it set bunched up while it's wet, either.

When you say .....
... what do you really mean?
dirty as in used a lot?
or dirty with what?

That may determine what best to use to "clean" it up.

My understanding is that vinegar to set colours, no longer works as today the fabric dyes are chemical oriented, whereas before they were organic/plant based dyes. Similarly salt used to be used to help set colours.

vinegar will not do anything for your quilt-
if you are worried about fabrics that might bleed throw in a couple color catchers- you could use synthropol which will keep fugative dyes in the water from getting on other fabrics.
put it into the wash with detergent- a gentle cycle- and wash it- you did not say what the fabrics are like---are they dark? light? thin? heavy? damaged at all? what is the backing like?
every quilt i make goes into the washer- with detergent- warm water- a regular cycle- and then i put them into the dryer- in the 25 years i've been doing this i've never had a quilt damaged by washing/drying it. i treat them exactly the way i think anyone would take care of any bedding....even the silk and wool ones- i know many people treat them as if they are some fragile...almost afraid to look at it wrong piece of antique tissue paper-
but i've never had a quilt that seemed that ... fragile to me-
if i can throw the $600 pottery barn quilt in the washer and dryer- i can do the same with the one i made...if its dirty and needs to be washed- wash it---what is the worst thing that can happen? it might come (undone) on a seam- you just fix it-
a color may bleed...there are products that will help with that (retayne, synthropol, color catchers)
if its usable it should be washable- only if its a wall hanging that was never meant to be washed should it not be washed.

vinegar only works on acid dyes- like the dyes used on wools...(animal fibers) it has no impact of the dyes used on regular cottons- it can help freshen/remove odors if that's an issue

Another consideration ... is this an "old" quilt ... where perhaps the fabric/fibres are fragile and could deteriorate with washing?