I had a bit of time spare to play around in the kitchen today, and I used it to try making my own jalapenos. I love those things, but they are a bit pricey. Also, homemade ones are just peppers and vinegar, so no random additives.
I'm not giving any specific quantities here, the only measure is having a glass jar to hand that will hold the quantity of peppers you have plus sufficient vinegar to cover them. You can buy glass jars from Lakeland, but why bother when you get washable ones free with so many foodstuffs?
Here's the technique I used, which seems so far to have worked:
Cut the peppers into rings and sprinkle them with salt. Leave for half an hour or so (about the time it takes to have a cup of tea - might not need that long but I was reading something engrossing).
Use your glass jar to measure the vinegar (in this case white wine vinegar) into a saucepan. Don't fill it up to the top, you need to allow room for displacement. (Although if Archimedes had been bathing in this stuff he would not have been shouting 'Eureka', unless it has a secret meaning along the line of 'my balls are on fire!')
Heat the vinegar. Add the peppers. Bring to the boil. Simmer for half an hour or so. Don't inhale the contents!
Allow to cool before putting in the jar. Keep in the fridge.