Temp guage jumps all over the place after I drive for about 30 minutes, and then the guage dances with the turn signal (left only), sometimes the electric fans work after I shut the Discovery off & sometimes they don't. Tonight on the way home, I had the AC on & the radio off so I could see if the fan were staying on, then I thought I heard what sounded like a relay clicking on & off under the dash area, so I turned the AC off. Temp guage went back to normal. Drove to the next light, but when I started to drive again, the spedometer stayed on "0". I know it was working fine till I stopped at that light. No bouncing like the search mentioned before this, just no speedometer, odometer or trip odometer. All the other guages work just fine. What the heck is going on??

 

God I hate electrical issues.
Sounds like a bad ground or a bad instrument cluster.
The guys that know electrical stuff better than I will chime in.

 

Take off the driver side kick panel and behind it is earth connection E201 for all the dash cluster. Check to be sure that is tight, all other connectors firmly plugged in. Ditto for ground bond from negative battery to frame, follow it down beside radiator. Try a battery jumper cable attached to negative battery and engine block or manifold. Shake the wire harness.

 

But it's more than likely not the alternator, correct?? Had visions of the frying one electrical device after the other after reading the search on this subject...

 

The alternator failing will turn off the tach drive signal. But rest of electronics continues to run on the battery power. You can measure battery volts and see if alternator is working (13.8 - 14.4 at idle). At about 17 volts you begine to fry things.

I got a plug in voltage tester from WalMart that plugs in the cigar lighter, and shows digital voltage. Less than $20, easier than holding meter leads on it while driving.

If alternator wasn't working you would have no tach, and no charge to battery, so soon truck would not crank up.

 

good to know... Will get one of those testers tomorrow & check the connections behind the kick panel to see where that brings me.

 

worth 1000 words....