If the speakers in your car are not working, randomly stopped working, or working intermittently, the most likely cause is the BM54 amp failing. Most common symptom is some speakers will be working while others will not, or, some speakers will randomly stop working and then work again. The amp fails due to constant temperature change. If yours fails on you, there is a fix! New amps are expensive, and used ones aren't cheap as well. The worst part is that no matter if you buy a new or used one, it will eventually fail on you in the future since it's a common problem of those amps. There is a company in Europe that sells a repair kit with instructions on how to install it for 49£ ($69) Here is a link to the website where you can buy it...
http://www.diyparadise.net/bm54.html
Basically, the repair involves using a solder gun. If you have no experience in electronics, or just don't want to mess with it yourself, then you can send your faulty amp to them and they will install the kit themselves for 99£ ($140) Yes I know, you can hunt a good deal on ebay and buy another amp for that amount. But the good thing about this fix is that it resolves the common issue and the amp will last forever, (well, not forever)
Note: The BM54 amp is located on the left inside the trunk area. You will have to remove the paneling to access it. The BM54 amp is the silver one, not the black one.
Just thought I would share this with the fam! Have a great day!