EDIT: This is on a 2000 4Runner

Ok, at a loss for what's wrong here. I'll start off by saying I'm a noob and don't have a multimeter (may be buying one later today though).

I ordered a new head unit, component speakers for front and rear doors, and tweeters from Crutchfield. I spent ~6 hours yesterday wrangling with installing all the items, only to find that once I was done, I have no sound coming from any speakers. I tested partway through (after new head unit and front passenger speaker and tweeter were installed) and everything worked as expected. Note: Since I've seen it asked inother audio problem threads, I did bypass the factory amp using the metra harnesses from Crutchfield.

I then proceeded to install the speakers in the remaining 3 doors, and after reconnecting the negative terminal, I tried starting the car and it wouldn't start...it would crank, but then die when releasing the key. I tried again and this time gave it a little gas, and the car came back to life with a pop (fuse?). I noticed this morning I have no turn signals, so I'm assuming at the least that fuse is blown and could've been the source of the pop when revving it to start (currently at work and didn't have pliers to pull the fuse in the parking lot this morning).

Has anyone ever had anything like this happen or can anyone provide any sort of guidance as to where to start? A multimeter from Amazon won't be here until tomorrow if I order, and I'm about to give up and take it to people who know what they're doing so I don't screw things up further

Sounds like you've got the power connected to the ground or something. Confirm when you can that a fuse has popped. Popping fuses indicates a short somewhere.

If it's the ACC fuse in the engine bay or the dome fuse in the drivers side kick panel, then you're radio power is somehow being grounded and popping the fuse:

Just checked now at lunch and all fuses seem to be fine. The turn signals are now working also, because I plugged the center trim/hazards plug back in. I didn't realize that needed to be connected for the turn signals to work. I'd left off all trim pieces to make it easier for someone to access/diagnose

Radio working and all?

For now I actually just unplugged the head unit altogether. I reached out to a friend at work who's an audiophile and we're going to meet up tomorrow after work to take a look and hopefully diagnose the problem

To update/close out this thread: the issue is fixed. After work yesterday I went through (with the help of Crutchfield) and disconnected all speakers and tested them one by one. Turns out the orientation of one of the rear speakers had the positive/negative terminal coming into contact with the foil backing of some sound deadening material I'd applied to the door, so after changing it's position, everything works as intended!

Awesome! Rock some Van Halen in celebration

When I installed an aftermarket head-unit, both rear speakers stopped working, but the fronts still play. I was hoping to find a similar solution, but I can't see any way for the contacts to have broken as I didn't replace any speakers.

Thank you for your information about installing speakers in car doors. It was useful when I did the same operation, I replaced my old speakers for new one's Pioneer TS A6970F model.
My old speakers had a very bad sound quality and i decided to change them. I'm not really good at sound systems, so I decided to find good source with recommendations about 6x9 speakers to decide which speakers I can buy. In the end, I found this top Best 6x9 Speakers | Audio Direct. At this website, you can find detailed info about sound systems, and recommendations with choosing good speakers/microphone/headset/etc. Maybe I will help someone with this info. Best wishes.