Next, you need to know how much current the turn-on lead of your desired amplifier draws. Occasionally the specification sheet for the amplifier will list it, but I usually need to measure it. Simply take your digital multimeter and set it to the DC Amps setting. You'll probably need to move the positive probe (red) to a different jack on the meter marked with the letter "A." Be careful! If you try to measure voltage this way, you'll short out the circuit and possibly damage the meter!
Connect one probe to the amplifier's turn-on lead and the other to +12-volt power. The digital multimeter will measure the current flowing flow through the meter to the amplifier. Let's imagine that you measure an unusually high 300 milliamps (0.3 A) of draw from the amplifier. If you were to connect that remote turn-on lead to the radio's turn-on lead, you'd likely damage the fragile transistor inside the radio that's supplying power to the circuit. Sorry it took six paragraphs to tell you it may not work, but I believe in teaching my students to find out how any situation behaves rather than just spit out the answer for this single instance.
Using an aftermarket OEM interface means that you have the benefit of circuitry that was designed to safely drive several amplifiers and other processors. If your Altima source unit is crude and doesn't need the advanced processing of some OEM interfaces, you can simply resort to the old dog's default -- wire in a standard Bosch relay to switch higher current when triggered by the low current of the factory radio.
Q: I recently purchased a '02 Cavalier and have looked at different audio stores and was still unable to come up with a wiring harness to use as a replacement to the factory stereo that I'm replacing with a Pioneer CD player. The problem I'm having with the installation is understanding what to do with the acc wire on the replacement CD player. I've been told that the Cavalier doesn't supply an ACC wire to the radio that's already in the car. Can you give me any information on which wire is which?
Thanks,
Jason
A: The two common methods of dealing with GM's infamous Class 2 serial data buss involve some sort of adapter. The "B" method uses an extension harness that keeps the factory radio connected to the vehicle's electrical system. It's long enough to allow you to jam the radio in a corner of the trunk so it can talk to the Class 2 data network in the car, but not get in your face. Now you have an empty radio opening in the dash, ready for some cool aftermarket product. Since you aren't really interfacing with the factory audio gear, you can expect great performance and no OEM annoyances as your dumb-as-a-stump factory radio acts as a decoy.
The preferred "A" method uses one of the many OEM interface adapters from companies like American International, Peripheral and Soundgate. These adapters talk to the network and provide aftermarket friendly input and output wires including the accessory wire that only exists in the factory electrical system as a software code. I'm surprised you didn't find one at the audio stores you visited. Try again or try some different stores. These interfaces are out there and ready to give you the results you really want.