One common cause as to why there is no sound output after a new stereo installation is the possibility of a Factory Amplifier installed in the vehicle. A sure indication of a factory amplified audio system is the presence of decals, or markings on the factory stereo, or on the door panels near the speakers. The decals or markings may show:
-BOSE, Infinity, JBL, Monsoon, Harman Kardon, Premium Sound, Active Sound, Concert Sound, and the like.
Some factory amplified audio systems may not have any markings or decals, such as some Toyota, Lexus, Ford, Nissan, GM vehicles, and others. These amplifiers are often hidden behind plastic interior panels and are difficult to find at times.
If you encounter a no-sound situation after the installation of an aftermarket stereo, there is one simple way to test for a factory amplifier using a multi-meter.
1. Using a digital or analog multi-meter, enable the meter to read resistance (OHM) in or near the 200 OHM range.
2. Gain access to the speaker wires on the vehicle harness, and ensure the speaker wires are disconnected from the stereo.
3. Connect the + (POS) probe from the meter to the + (POS) speaker wire you are testing.
4. Connect the – (NEG) probe from the meter to the – (NEG) speaker wire you are testing.
5. Read the resistance on the meter, and ensure your fingers are not touching the wires or probes.
If the resistance of the speaker is within the range of 2-10 ohms, this will indicate that the wire does not pass through any amplifiers before it reaches the speaker. In this case, the no sound issue may be caused by another speaker (Most Likely, or the stereo may have a genuine issue with the sound output (Less Likely).
However, if the meter reads above 10 ohms, or into the thousands of ohms of resistance, this may indicate a blown speaker, faulty wiring, in-line amplifier, or crossover circuit is installed. In this case, it is highly recommended to test the rest of the speaker wiring and compare the results.
-If one speaker measures a high resistance, this may indicate that one speaker is damaged, or the speaker wiring is faulty. Re-test this speaker, and check all connections.
-If two speakers show a high resistance, and two others measure between the 2-10 ohm range, this may indicate that an amplifier may be installed for only the front, or rear speakers. For example, this is common on the rear speakers of certain BOSE equipped Nissan vehicles. Please re-test the speaker wiring to confirm.