The oil light lamp is probably burnt out.

Because the key warning works, it sounds as if the door switch is ok,
which suggests it maybe a relay or logic unit at fault.
Unfortunately, the online manual at MX-3.com doesn't have the
electrical section. A friendly Mazda dealer might let you have a
look at his.

--- In mazdamx3ownersuk@y..., blackfrothyguinness <no_reply@y...>
wrote:
> My MX3 is my third Mazda and i thought it should have a low oil
> light, as the other 2 did. It doesnt seem to light nor do i get
> beeped at when i leave my lights on, which has twice led to a flat
> battery :(
>
> My key in ignition warning works though as does everything else
> which aint bad for a 91 car full of electrics :)
>
>