when driving i have noticed the lights go dim a bit then back to normal, lately the battery and brake light will both come on at the same time then go off. it seems to do it more on higher rpm's i have checked voltage and it drops to about 12 volts when the light comes on.


im guessing its the alternator?


thanks, rob

 

I have a 98 with the exact same problem. I took it in , and had them check the battery/alternator while the vehicle is running... When revved up,, the charge went haywire, and he was not able to tell for sure if it's the alternator, so I'm pulling it off this weekend, and swapping it out.

 

Battery and brake light at the same time is almost always a bad alternator. Dont buy just any auto parts store alternator because you will be chaning it again soon. Isuzus eat aftermarket ones for some reason.

OEM and Bosch are the only ones I've seen that last in these trucks.

 

yeah electrical problems that vary with RPMs like surges and brownouts will almost (but not always) indicate a faulty alternator. Buy a replacement with a lifetime warranty.