So I drove the car today no problems at all for about 100 miles. it was driven in 50-40 degree f weather. Well I parked at my buddies house and when I left it is 36*F. All of sudden my rpm gauge isn't working and my battery light is on. I managed to get back home with no problems. Any input on what could be going on? It has a brand new alternator from when I purchased the truck a month or so ago. No problems prior. Hopefully someone can inform me of some fixes..? or known issues.

 

Check the wires to the alternator, I'm guessing one is loose. Tighten all the bolts on the connections at the alternator and you should be good.

Maybe a senior member with more experience can confirm.

 

Drag out your multimeter and make sure you're charging voltage is correct. and check that little white wire that has a single speed spade lug connection to the back of the alternator, that is what sends the signal to the tachometer, rpm is measured off alternator frequency

 

check that alternator real well. grounds and wires. is it a cheap auto zone rebuild? i went through six of these they overheat easy and brushes get destroyed even when truck isnt hot at all. the loaction of the alt. just subjects it to a lot of heat. i had these same problems but start simple and check for corrosion and such at grounds and check wire placement is tight.