I don't know anything about non-factory alarm systems, but I've repaired over 2000 factory radios since the early '90s. There is absolutely no way any of them would draw a quarter amp for just the memory circuit. Many older GM radios draw over three amps when they hit a loud bass note. My power supply had a two-amp over-current cutout that regularly tripped so I had to upgrade to a better one years ago. Chrysler radios produce the same sound while barely drawing an amp. The needle on the ammeter doesn't even move when only the memory circuit is turned on for either of those radios or for Ford radios.
Also, I sell and repair radios at the nation's second largest old car show swap meet at Iola, WI. Twelve radios are powered up on display and run off solar panels and batteries. With one of the batteries later found to be defective, one radio turned on killed the battery each night about three hours after the sun went down. Later, those same batteries kept all 12 memories alive for two weeks when I forgot to turn the switch off. That shows how little current memory circuits draw.
Many memory circuits have a large surge current when the radio is first plugged in or the battery cables are reconnected. All microprocessor circuits including those in radios have a "reset" circuit that turns the thousands of transistors in integrated circuits on or off to their initialized starting points. Those reset transistors have to pass up to an amp during that surge but they are only rated at about 50 milliamps. I know this because there was a common problem with one model that developed bad solder connections. That one amp current surge didn't last anywhere near long enough to overheat the transistor, but road vibration and bad solder connections caused that circuit to turn on and off repeatedly until finally the reset transistor exploded. I spent a lot of time figuring out how that circuit worked and why it was failing, and in the end, testing showed those radios drew less than 5 milliamps for the memory. Once a capacitor charged up, (in a tiny fraction of a second), the circuit couldn't possibly draw higher current. There was nowhere for it to go.
Given that cars today need Body Computers, Transmission Computers, Remote Keyless Entry Computers, Memory seat modules, auto-load leveling computers, Air Bag Computers, and Anti-Lock Brake Computers to do things computers were never needed for before, (and they all have memory circuits that constantly draw current), Chrysler STILL lists 35 milliamps as the maximum allowable battery drain. You can even add a GPS radio to the list. If "ignition-off draw" is found to be over.035 amps, you have a legitimate warranty claim.
A 159 "peanut" bulb left on in a glove box draws half an amp, and that will kill a battery overnight. Too many maps and other papers stuffed in the glove box of a Dynasty caused the light switch mounting tab to bend so the light never turned off. That became a common problem but the first one took a little detective work. The drain was just under half an amp. I was involved with dozens of those. The complaint was always the same. "Car ran fine last night; battery was low this morning". The repair was always the same. Take 10 seconds to bend the tab straight and another minute to explain to the owner how to prevent it from happening again.
Rivermikerat, if your radio is wired to remain powered up all the time, it could easily draw the half amp you listed, but the memory circuit alone absolutely, positively will not draw anywhere near that much by itself. Simple math will prove that. There are too many large-value resistors in that circuit that limit current flow to a very low value. You can't get much water through a garden hose when you're standing on it, and you can't have much current flow when it's restricted with resistors. The only exception would be if the diode between the switched and memory 12 volt lines is shorted but that's very rare. The symptom would be the radio can be turned on any time, even with the ignition switch off, and with the radio wired properly.
Is it possible your aftermarket alarm is wired into the radio's memory circuit and you're reading the current drawn by both items? And why would you put an alarm in an Escort? That makes as much sense as putting one in my '88 Grand Caravan. I love and trust my van immensely, but I'd also love to have someone steel it so I could head south and find a nice rust-free one just like it. :)
Tuesday, January 3rd, 2012 AT 6:09 AM