jrp1588

2003 Mustang GT with a Mach 460 sound system. The system has no bass what so ever. Sound seems to be coming from all speakers, but no bass.

I folded down the back seats and took a look at the amps. I found that a small gray plug halfway between the 2 amps was unplugged. I plugged the wires back together and turned on the car. It now produced no sound. I adjusted the volume and heard a few popping noises coming from the speakers. I continued to fiddle with the volume and at some levels heard very low distorted music coming from the back speakers.

Is one of the amps blown? Both perhaps? I don't know much about audio, but I thought I read that if the amps were unplugged, the rear speakers and large door speakers wouldn't work. What do you guys think.

ttocs

probably means that someone has messed with it while installing an aftermarket radio at some point. Have you checked any fuses?

jrp1588

Checked the fuses, couldn't find anything wrong. It does appear that there used to be an aftermarket system before, there is some non-stock wiring at least. Where should I go from here?

11GTdriver

Start at the main cable that snakes around the Mach box in the rear. On the '03, behind the rear quarter trim on the driver's side there is a couple of connector's to this wiring harness. If you know someone who can help, I would check for continuity using a multimeter set to Ohms and ensure there isn't any high resistance in the cable from the connectors behind the quarter trim, to the connectors on the Mach box in the rear. If you can, pull the entire Mach box with the harness still attached up to the two connectors behind the quarter interior trim. This will also facilitate the ability to remove any of the aftermarket wiring that might be left. Hopefully the previous owner didn't hack into the stock harness badly. If so, you might consider just replacing the harness entirely. I have a replacement harness for this is you are interested.

If all is well with the harness from the rear quarter and back, I would check the harness from the rear quarter trim connectors and forward to behind the driver's side kick panel where they connect to yet another pair of connectors there and do the same... check for continuity. Hopefully this part of the harness isn't hacked into at all.

Pull the headunit and ensure the wires behind the headunit are not hacked into or have exposed mesh. Behind the headunit is usually where things get tacky with people who don't know jack about wiring. Typically things are not placed back the way they should be when people get ready to sell a car and return it to stock.

In the end, as you check all the wiring, look for obvious chaffs in the wire, areas that the wires may have become smashed or pinched and of course any exposed wire. Pay special attention to the pins inside the connectors as well. Ensure they do not appear recessed or burned as that would indicate a short.

Ideally use heatshrink that you can buy from places such as Radio Shack to cover exposed areas of wires, provided the lay of the wire under the insulation isn't birdcaged or heavily disturbed. Otherwise, good 'ole insulation tape will do. The idea is to keep the wires from shorting against the metal of the car.

If none of this works, and the wires, connectors and pins all appear structurally sound, I would start suspecting either the headunit or the rear amps. On the '02+ Mach 460 with the 6CD changer setup, unlike the 94-01, there is no amp under the radio, it is integrated into the headunit. I hope this helps some.

jrp1588

I have pulled the head unit before, and I know the wiring behind that looked totally stock. It's the stuff around the amps that looks aftermarket. Will I have to pull out half of my interior to check these wires you're talking about or will they be accessible?

Any way I can test the amp itself since they are easily accessible?

11GTdriver

You can test the amp input to output with a multimeter set to Ohms pin-to-pin one at a time, but that really won't tell you if the amp is bad or not. You can take the amp off the Mach box in the back, take off the backing plate of the amp and have a look inside at the circuit card for anything that would look obvious as far as damage. Look for things like blown capacitors, which when they go is very obvious, usually because they blow their tops. Resistors, diodes, IC's and usually a lot harder to visually see if they are bad.

You can also try placing the red and black probes of a multimeter set to Ohms on opposite sides of leads on components such as capacitors, diodes, resistors and the inductor coil on the amp's board if you want and see if any of them are open, which would indicate a failed component. This method however, cannot tell you if say for example, if a capacitor is on it's way to failure. The capacitor, one lead to the other, may show good continuity, however the capacitor, may not be preforming to it's original intended specification and therefore may be 'bad' as far as the expected tolerances to the amp in which the Mach 460, as a system, expects.

Once I had a blown Mach amp and there wasn't anything obvious on the top of the board that looked bad, but when I pulled the board out of the metal housing that made up the 'amp' as it were, there was a nice burn mark under the board on the metal, so I just ended up tossing it and getting another from the bone yard because they're a dime a dozen, at least they were a couple of years back. That failed component was a bad capacitor, though it looked visually fine on top of the board.

Honestly the only way to troubleshoot the amp effectively is to either have a troubleshooting manual from Visteon (good luck), with all the intricate details of that amp, or access to a Huntron Diagnostic Bench that allows a tech to individually and visually inspect each discrete component or IC while in-circuit.

I know that's not exactly what you want to hear, but finding a schematic to even troubleshoot that thing for me I found to be impossible. I ended up following the runs from component-to-component, ensuring the runs looked good and used a Huntron to eventually find the bad component(s).

As for pulling the rear Mach box out, you'll have to remove your rear seat, speaker package tray behind the rear seat below the rear window, interior door runner trim and the rear quarter trim panel. There are nuts below the speaker package tray that must be undone, as well as (I believe to be) two or maybe three larger nuts holding the Mach box above the trunk interior that must be done to drop the box. Having a person help you remove the Mach box is a huge help because the darn thing just likes to drop to the trunk floor when you release all the nuts from top and bottom and that can inadvertently pull on the harness back there, unless you want to go through the trouble trying to remove it from the Mach box before you drop it. (ask me how I know this) lolz

jrp1588

Sounds complicated. I hate working with electronics. I think I'll wait till the spring before I tear into it. Or I may cop out and take it to a place that specializes in car audio and have them look at it.

ttocs

can you get a pic of what you think is aftermarket?

jrp1588

Yeah, I'll take a shot tomorrow after work.

jrp1588

Alright, I took a few shots of the suspect wiring.


here's a closeup


and a shot from either side so you know where we're looking at. This is in the trunk between the amps