ghost HUD

[89 coupe]

my hud is acting very weird lol. it was working when i bought the car. then it stopped. i know this is normal but then after a while it starts working again. but instead of reading 0km/h when stoped its all over the place until i start moving. then she conked out again. today i just realized that when i turn my hazards on then off it comes on aha. but like before when im stopped its all over the place but when im moving its working. any one know what causing this.