Selling alcohol in Thailand is banned during election voting. Grocery stores, convenience stores, bars and restaurants will not be selling or serving. Those in need- your best bet is a local convenience store; 7-11 will not be selling.
Alcohol sales will be banned from 6pm on 2 July (Saturday) until midnight on Sunday (really Monday morning)- this means bars or restaurants will serve on Saturday night or during the day/evening Sunday. Many bars will not open on Saturday and might not open on Sunday.
Yes, this is crazy.
Polls will be open for voting on 3 July (Sunday)- you cannot drink the evening prior to prevent “vote buying”. What is really crazy- the polls are scheduled to close at 3pm on Sunday afternoon, but you cannot drink until midnight. Really. I’m not making this up.
So, stock up on Friday night and Saturday before 6pm. If you are headed out for a dinner on Saturday or Sunday- call the restaurant (most will not serve alcohol). If you want to have a drink with dinner- check with a western owned hotel as many will serve alcohol (but not near a window or outside).
Farang ( ฝรั่ง) In Bangkok 
Your post is a bit confusing. “Alcohol sales will be banned from 6pm on 2 July (Saturday) until midnight on Sunday (really Monday morning)- this means bars or restaurants will serve on Saturday night or during the day/evening Sunday.”
So bars and restaurants will serve even though it’s banned tonight (Sunday)? On another note, I had no trouble finding alcohol on the river canals today as long as I drank it in the boat but not on land. That was a nice bit of news for me. It’s not only your post that confuses me, it seems no one here in Bangkok really knows what/when/if alcohol will be sold- even the Thais are confused by this. 🙂 It’s almost comical!