Car Stereos: Car amplifier trigger voltage, amp trigger, mercury villager

Question
QUESTION: I have a 1998 Mercury villager with a factory four speaker amplified system.  The CD Multi changer went out, then the tape
player choked and I couldn't feed it an AUX input via tape so I
put in a Kenwood KDC-248U late last year 11/2011.  Worked Great.

Today, 6/6/2012, it quit giving me any output. The Amp trigger pin
(for the blue/white wire) is only producing 1.1 volts.  I know the
old ford system used 5 volts, but I don't know what the Kenwood
SHOULD produce, only what it is. Should it be 12 volts?  Is it fried?  Should I buy a trigger unit?  When I manually feed the amp trigger lead 12 volts everything works fine even though it's built for 5 volts.  This Kenwood is only a couple of months old.  Thots?

ANSWER: Hi Rich,

The output voltage on the amp turn-on wire isn't particularly important.  It just flips a relay.  It needs to be a reasonable amount of DC power to activate the electro magnet in the relay.  My guess is anything > 3-4V would do it.

The amp power on wire coming out of your Kenwood should be providing 12V of power.  1.1V definitely doesn't sound right.

It sounds to me like your deck is in need of replacement, or you can try and hack around it with some other sort of device like you've mentioned.

(You could also use the power antenna wire; but some decks turn that off when you're not in AM/FM mode.)

Justin

---------- FOLLOW-UP ----------

QUESTION: Justin,

Thanx for the info. My local Kenwood service center repaired my unit and
now produces 12V for amp turn-on.  While it was in the shop I measured the current draw on the original equipment: it was 450 mA at 4.4V,so it's probably a coil-based relay.

It looks like they replaced a capacitor to fix the radio.
Surfing the internet at http://www.bcae1.com/amplfier.htm I see that many
new high power amps draw less than 50 mA at 12V, So I guess they have transistor-based switches. Maybe this new radio can't effectively power my amp's turn-on relay.  How do I find out?

Maybe I just got a transient current spike and I should protect with a relay.  But they draw too.  Maybe I should just get a harness and bypass the amp.  I haven't reinstalled the new radio yet. Thots?

Answer
Hi Rich,

4.4V @ 450mA sounds like a LOT of power for an amp turn-on.  I think maybe putting a relay into that circuit might be a good idea -- that kind of a draw may have been what ended up being the demise of the components of your deck originally.

Justin