1996 GMC Jimmy 6 cyl Four Wheel Drive Automatic 56000 miles
the speedometer quits working once headlamps or parking lamps are on, but it is not effected by daytime running lites. So at nite I set cruise control and it works fine but the speedometer does not move. Once you stop for 5 or 10 minutes it will then work fine for another 10 minutes then hand will remain stationary.
But the cruise works when the speedo doesnt? The Speed sensor feeds info to the PCM (computer) it in turn gives a signal out to the speedo for how fast you are going. I would look for a loose/poor connection in the back of the instrument cluster. Sounds like it is losing something when the lights come on, which could be an indicator of a bad connection that cant handle any load on it