03 Tacoma Strange Noise

2003 Taco 320K miles Frame #2. About a month ago on the way home from a PSF fix. The horn was sounding constantly as I drove. Several freedom birds sent my way. Figured out that the horn stopped when I turned the lights off. Simple fix - unplugged the horn.

A few weeks later. I went outside this morning to leave for work. Loud constant ringing sound coming from under the hood. Seems to be emanating from the battery/fuse box area. Started right up and the sound stopped when I turned the lights on. Parking lights only - no noise. I left the parking lights on all day at work to stop the noise. Expected to need a jump start - not so. Started right up and no noise all the way home. A few hours later I was bringing the trash out, about 7:15, and the alarm sound was going again. I unhooked the battery until tomorrow morning.

This truck has never had an alarm of any sort factory or otherwise. Any ideas what's going on here? Any suggestions or help appreciated.

 

Welcome aboard, I'm sure others will chime in with better info. First thought is a stuck relay. I would disconnect the battery (don't skip this part, see below) then open the under-hood fuse box, pull the relays and test/replace them.

Word of warning here, careful while doing this, there are hot wires connected to the relays and if one of them gets a short it will fry the whole wire (if you're lucky, that's all) and you'll have to pull the fuse box to replace the wire. Don't ask how I know.

 

Lol thanks I’ll give it a try.

 

I worked my way through the relays and it didn't help. Now I'm seeing on line that it might be an alternator. This is what I found:

A common noise from a failing alternator is a high-pitched whining or whirring sound. This noise is typically caused by worn-out bearings within the alternator. As the bearings wear down, they can produce a continuous or intermittent whining noise. However, you may hear clicking noises too.

Replacing an alternator is above my pay (ability) grade, but I think my brother can do it. Wish me luck. Thanks!