how can i fix N reg Ford Fiesta 1.25 Ghia?

If it was OK before the stereo was fitted then that's likely to be the cause of the problem.
If whoever fitted it didn't use the original wiring, but chopped into the loom to get live feeds, earths, etc, they may have tapped into the immobiliser wiring, which is putting on the hazard flashers.

However it's also possible that the immobiliser is faulty. They take about a minute to arm, so it might also be worth checking the door, tailgate and bonnet switches for correct operation and that the wires are still attached to the switches.

Phil
July 2008