I have a 1994 Mazda B4000 that has been having some problems with the turn signals/brake lights/taillights. I have just replaced the multifunction switch (about 3 months ago). I have two flashers that I can switch out, one is a heavy duty. I replaced the bulbs in the left front and left rear turn signals, even though the old ones were working in the same manner as described here.

Here's what's going on:
With old flasher (not heavy duty):
Hazards: OK speed, but brake lights flashing too
Left Turn: too fast
Right Turn: very slow or always on
Brakes: rear turn signals illuminate with brakes, but don't flash; front turn signals do not illuminate
Brakes + Hazard: brakes and hazards always on (don't flash)
Brakes + Left Turn: brakes on; turn signal on, but doesn't flash
Brakes + Right Turn: brakes on; LEFT turn signal on, not flashing; right turn signal flashing slowly

With new flasher (heavy duty):
Same as with old flasher, except:
Left Turn: OK speed, but brake lights flashing too
Right Turn: OK

Sorry for the long post. I've looked for answers in other posts but wasn't really able to find anything.

 

Bad grounds and rusted bulb sockets would be the most common problem on a vehicle of that age.

 

I would also suggest checking your grounds for all of the lights, headlights too.

What did you change just before the trouble started ?

Any light bulb work, i.e. LEDs ?

Also, look at the connector for the Multi-function switch, sometimes the little tabs that hold the pins in the connector break off, maybe shorting.

Just thinking out loud.