Tach jumping when lights on.

[DMAN302]

Just noticed when I turn my lights on that my tach and voltage gauge seem to be jumping up and down about 100-300 rpm on the tach and 1-2 lines on the volt gauge while my idle is solid at 900 and my autometer tach is steady. All ground wires are new (last 3months) and doesn't seem to happen when lights are off, other than that I have not electrical problems to speak of..car starts fine and accesories run good, alternator, grounds, selenoid are new...anyone??

 

[fordman54935]

How new is your battery? I had battery problems on my 93 LX 2.3 and it made my tachometer and voltmeter (stock gauges) jump all over.

Gauges are very electrically sensitive components on a car, and battery problems will make the gauges do all sorts of crazy stuff.

I'd have your battery checked. Most parts stores do it for free so it can be checked under load.

Hope this helps!

 

[ka0tyk]

when my battery got low my autometer tach would jump...

 

[88stangmangt]

idle spike or low battery.

 

[BnGRacing]

90% of electrical gremlins are a bad ground somewhere. My dash did the same thing & I hooked up a meter to check voltage while I was driving. Voltage dropped to 10.4 and all the way up to over 17v. I figured a bad voltage regulator in the alternator - WRONG! I had a bad ground. I replaced the factory grounds with better wires and grounded the alt. directly to the battery - problem solved.

 

[blk92stangg]

My car was the same...fixed it by cleaning and sanding down the battery terminals and cables.

 

[DMAN302]

Well great advice!!, like I said I did replace the ground from battery to block and new cables from battery (pos and neg) with new battery and new alt. I wonder if anyone can tell me how many and where abouts other grounds might be..I will go through and check all the wires but info on where to look is appreciated..I will start tonight.