you should be able to find a shop manual at the local library with the right information on this -- make copies of the pages, as they are usually for REFERENCE only...:)
The backup light switch is located on the left side of the transmission. Disconnect the switch connectors, then unscrew the switch.
There is no egr valve on a 1990 Mazda MPV 6 cylinder
The 1990 Mazda 323 horn relay switch can be found on the front drivers side quarter panel. The relay switch will be on the inside of the quarter panel.
in the tank
blown wire/fuse
in the gas tank ?
Yes.
Underneath the car bolted to the bellhousing on the gearbox
The switch is located on the driverside just past the fuses towards the break pedal.
The brake light switch is located on a bracket behind the brake pedal support.
it is located on the transmission itself
On the steering column????