My battery gage will be at about 16 volts when I first start my truck it's a 1990 toyota pickup but when it gets hot it wil drop to about 12 volts and then my lights will dim and dashboard lights will dim also I have a brand new alternator and battery in it and it still does it. Any answers??

 

It is not working like it should.

Maybe it is like me and does not like it hot!!



What gets Hot??

Ambient air temperature???

The engine temperature ??

The battery or the alternator??

What kind of voltage do you read at the battery??

What voltage at the B terminal of the alternator??

Battery terminals clean and tight??

Ground cables clean and tight

Did you put on a new belt with the alternator ??

Did you get it tight ??? Is it staying tight ??

This should get you started let us know the results

 

My 86 pickups battery died in the heat so I removed the battery for 2 days left it in the shade and put it back in yesterday and it started first crank. So the heat can zap it but I'm not sure how to really prevent it from happening again and I'm not sure how to fix it quickly with out a jump.
Its a 22re no a/c