led or shift lights to indicate speed.

If it's a pulse type speedo sender unit (as many Nissan cars have), then a Frequency to Voltage converter (LM2907) feeding a LED bargraph (or dot) driver (eg, one LM3914 per 10 LEDs), or maybe a range-converted LED tacho. If its a mechanical speedo, then you need to add a pulse or voltage generator. I sensed the spinning magnet in my mechanical speedo, but you may be able to get a T-piece and add a Nissan pulse sender to the gearbox cable output. If you have a voltage generator, then the pulse (frequency) to voltage converter can be omitted. Mind you, these days people probably use PICs or Arduinos etc to convert and drive displays. Then it's easy to program flashing etc if a speed is exceeded, or light extra LEDs for warnings.