Car Alarms: 18-20 volts being indicated, chevy suburban, reputable shop

Question
1983 chevy suburban, 3/4 ton 4wd, 5.7 liter. I bought the vehicle with a Code Alarm alarm system installed -previous owner had it installed for the convenience of keyless entry- but the alarm went haywire the other day and almost left me stranded in the desert. By haywire i mean it just kept going off all day, i disconnected the horn a LONG time ago, so it didn't bother us until i tried to start it. I pressed the disarm button on the fob, and nothing happened. I assumed the vehicle battery was dead, so i put it to a charger, and the charger listed the battery as fully charged. I could turn on my headlights, and interior lights, but everything else was dead. After some testing on the wires going to the alarm, we came to the conclusion that the alarm was getting no power, so we hot wired a relay that the alarm was connected to, and got the vehicle to start, though the dash indicator showed in excess of 18 volts in the system. I drove it home like this (a 2 hour drive)(and smelled some smoke from overloaded wires) and subsequently removed the alarm system, but i'm still showing 18-20 volts on the indicator, as well as on an external voltmeter. I thought it was a bad alternator, so i bought a new one from Napa, and am still in the same predicament. I will pay you for your diagram, i just have no idea where to start?   thanks in advance, mike

Answer
From the desk of AJ IBARRA.
ALARMTEK certified Technican:

It sounds to me like he has one of a few problems going on.  keep in mind there may have been an underlying problem with the alarm, however that is a separate issue from the electrical overcharge problem he has stated.

Could be loose connections at the battery or at the alternator. If these connections are tight and clean then check the voltage at the battery when the engine is running, if it is 16 volts or so , verify that the battery does not have a shorted cell, If not i suspect a bad regulator in the alternator.
To be sure have a reputable shop perform an electrical systems test on it. should cost around 25 bucks and have them verify your complaint.

Since you already replaced the alternator and the problem has persisted i suspect you have a bad battery, probably with a shorted cell.  It could be a connection issue however i doubt it, as you would most likely smell a "rotten eggs" smell from literally cooking the battery.

If it's going above 15 volts at any time, either your battery is really bad, or your regulator is bad.
Check the battery voltage with the car off. You can buy a digital multimeter for about $20 these days.

AJ
AJ@ALARMTEKS.COM