Had some issues with the 1998 tacoma 2.7 tonight.

Drove back from school this afternoon and met my family for dinner. Ran lights the whole way, no issues less it felt a little gutless at times.
Start it up from dinner, cranks a little weak. Head to my buddies work and hang with him for a while. Crank it again (dark by now), cranks weak again, flip lights on, dash lights and headlights very dim and getting dimmer. I park it and we go to a bonfire. Crank it up afterwords, cranks scarily slow. Flips lights on and dash lights are almost non-existant. Run the parks tailing my buddy at 15mph clear out of town. Hit the edge of town and flip on the headlights. Get (for the first time) the battery light. Also it begins to cut out. I run the parks for a while longer than the battery light comes on and stays on. I barely make it home limping along with it cutting out occassionally.

Me and my buddy cleaned the positive it was a little corroded but no change. I'm thinking its either the alternator or the battery. I'm leaning towards battery cause its very old (10+ years) and its acted weak a time or two before. Not to say its not the alternator just I'm checking the battery first.

Any help would be nice

 

Sounds like the alternator. The battery light is a CHARGE light meaning the system isn't putting out 14V at ~1500.

Take your volt meter and see what kind of voltage you get when you rev the truck up to ~1500/2000 RPMs.
Basically anything less then 13V your not charging worth a damn.

Of course, early failure on the alternator could be because the battery won't hold a charge and the alternator is working full time.

EDIT: Also, the truck can (well, should be able to [with a healthy alternator]) run without the battery connected to the system. Disconnecting the battery and seeing if it dies is a poor mans test. If you do this and it dies the alternator isn't doing its job. If it stays on the alternator is fine.
I still think its the alternator though.

 

Scuba means disconnecting the battery.

as in take the cable off....not disconnect the alternator.

it does actually sound like the Alt. though..and he is right about the battery being dead and making the Alt. work overtime.

 

Thanks for the advice guys but I've heard its not a good idea to disconnect battery while running something about it being a buffer for alternator and can actually lead to failure? Maybe just heresay?

Anyway I'll check tomorrow morning but my luck it'll be the $130 alternator

 

If it is the alternator I'd bet it's just the brushes. I wouldn't give that oem alternator to the parts store for the core charge. I'd replace the brushes in it and go from there. If you don't want to go through that hassle, lmk I might be willing to buy it from you if it is infact the original denso unit.
Good luck.

 

I'll cross that bridge when I come to it but if you'll pay me the core cost, you're more than welcome to it

 

Diagnostic Report from this morning. Started off cleaning the terminals good. Then took it for a test drive with lights, defrost, radio running, seemed a ok.

Checked with a volt meter. At idle with everything on it had ~12.7v. When revved it got ~13.5v at about 1500-2000. This sound normal?

 

Sounds like the alternator is working. Go to the auto parts store & have the battery tested.

 

agreed, have the parts store test the battery.

 

10-4 Guys I'll stop past Les Schwabs seeing as its a les schwab battery. Hopefully that fixes it.

Actually, I drove it to school this morning (headlights off) and it didn't have any issues and seemed to crank up fine when I got here. Still I'll have the battery tested.

 

Next time test it with all the accessories OFF. It does sound like the alternator is working though. 13.5 with accessory draw sounds semi normal.

 

Turns out the alternator is on its way out. Battery has 13.0 with engine off start it and it goes to 12.1. It won't raise above 13 til 2-3k RPM. Battery checks fine.