Fuse box mr2 - 1986 Toyota MR2

Go HERE.

should be on the drivers side under the dash

hopefully this forum will answer your question.
seems 2 under hood and 1 inside.
https://www.honestjohn.co.uk/forum/post/index.htm?t=69257

Is it in the foot well on the right, just above right of the accerator pedal.

The mechanic should check on the connection of the wires to the battery and the ignition system . Because of may be there is a wire that have been accidentally been disconnected. When you remove the the speaker box , and the amps out of the car.Check the wires , the fuses and the ignition switch and the ignition switch wires and fuses. It is because when you place the amps and the speaker box ,May be there is a wire that you accidentally disconnected that's why it wont start.When you place back all the equipment to the car.

Before you start looking a the fuse box, make sure of 2 things: do you have power and a good ground at the light housing. Then, make sure that the door switches are grounded good, and are actually working. If no power, get back to me and I will get you to the fuse box, altho I doubt that the fuse box is the root cause.

If they hooked the battery up backwards, they fried a whole lot more than the fuse box. Probably a couple of fusible links, coulda taken out the computer and a ton of other parts, depending on how fast the fuses blew. Fuses are designed to stop a current SURGE from damaging anything, but NOT current going the wrong way. While they will still blow, the damage may have already been done. 6v53 is right. Make Sears pay!!!

Try under the hood near the right side of the car. There are also a couple of fuse boxes with fuses for things under the motor bonnet in the rear. They should be labeled and they are covered with black covers. Hope this helps.

Take the negative cable off again and press and hold the brake pedal down for about 10 seconds. What that does is drains the power from all the capacitors in the engine's computer and will reset the computer properly otherwise leave it off overnight. Let me know how it goes.

The 15 amp TAIL fuse is for the sidemarkers, the license plate, etc. There is a taillamp relay.
Both of these circuits are powered by the 50 amp AM1 fuse.

The fog lights are powered by the 15 amp FR FOG fuse.

The inst panel is powered by 3 fuses: 7.5 amp GAUGE, 15 amp DOME and 7.5 ECU-B.

Please check all of these, and if they are all good, please get back to me for more info.
Hope this helps.