Car alarm problem with 1990 4Runner

My battery was recently disconnected and when reconnected the factory car alarm started going off. It goes off for about 30 seconds and then the vehicle won't start. Sometimes I can unlock the doors without it going off, but either way it won't start.

I have no idea why, but once the alarm stopped after I turned the ignition and hit the Valet Mode button. I was able to drive it for a few days. I would unlock the door and start it quickly because the red light on the alarm would start flashing rapidly, like it was about to go off. One day I forgot to start it within a few seconds of unlocking the door and it went off. Since then I haven't been able to get the Valet Mode button to work like it did before. It has a switch with two positions: the left is "Horn Defeat" and then there is a middle position; the right is "Valet Mode" but that's not a permanet position. Neither position seems to make a difference in preventing or stopping the alarm.

I've only had the vehicle a little over a year. I don't have a remote or a manual. I bought a manual but it doesn't have anything about alarm systems. The previous owner said he didn't know anything about the alarm but that I just shouldn't mess with it. I'd just like to disable the whole thing. The Toyota dealer said I'd have to tow it down there but I've read a lot of horror stories about dealers on these types of forums.

Any painless solutions?

Thank you.

Rip out the horn

I couldn't get any automotive place, even those that deal with alarm systems, to touch it. I had to have it towed to the dealer and have them uninstall it. It cost $120 but I never have to worry about it going off again.