so the other day my friend hooked the battery cables backwards on my car and it completely shut off. i changed the battery on my car, and the car started up no problem.

the only ongoing issue now is that i have no interior lights, no sterio, no dome light, no lights except when my headlights are on but thats it for exterior and my brake light works only when i put my
foot on the brake.

i checked both fuse boxes, the one under the hood, and the one under the dash. all the fuses are good, i checked them with my dads fuse tester. disconnected the battery for like twenty mins trying to restart the computer, no luck.

there is a CEL that comes on when i start my car everytime, and it never was there before. most people say i fried my computer but i dont think the car would even work if the computer was fried..

i couldnt find the computer in the car to disconnect the plugs on that to see if that would fix the problem, anyone can tell me where the ECU is at? or anyone have any suggestions on my issue? much appreciated..

i have a 97 mazda protege 1.6L 5speed

 

hmm ur ecu should be under ur dash.

 

If all you did was use a test light to check the fuses. You should really pull them out and check them they could be melted inside not feeding power to the circuit but still check good with a test light.

 

Room fuse runs all that-have you checked?

 

Lecture time

For all reading Moral of story...slow down pay attention and look at what you are doing. Batteries sometimes explode connecting them up wrong. Sometimes the protection circuits like fuses do not work fast enough and you fry vital and expensive electrical components like the ECU or worse melt adjoining wires and the harness may need to be replaced. In some rare cases you can start a fire that can destroy many parts not only electrical but mechanical in the engine compartment

Installation hints installing the battery correctly.

If the battery is being replaced and nothing has been altered or modified from the stock battery and it parts then anything different should be time to stop and look what you are doing!

Top post battery:
The positive terminal on the battery is larger than the negative post as is the battery cable connections .
The battery cable is the correct length for the proper battery and its position in the batter tray, if the correct battery is used. and installed in the battery tray, stock location unaltered. This includes the cables and any position fasteners or cable brackets.

Side post:
The battery cables are the correct length for the proper position of the battery terminals if the correct battery is used. This includes the cables and any position fasteners or cable brackets. and installed in the battery tray, stock location unaltered.