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I'm trying to integrate aux input to the stock amp on my sister's 1993 Volvo 240 wagon. The amp takes a 6 pin "DIN" input plug from the radio. Some Volvo forums unclearly report that the pins represent the positive wire of four speakers, a shared negative wire for the speakers, and remote amp turn on.

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Any idea how I can determine which wires are which, or if this estimate is even correct? I tried a voltmeter to the radio's 6 pin output, assuming that adjusting the fade/balance to play through one speaker at a time would show signal only on that line. Unfortunately not so.

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I grounded the voltmeter to the power/control harness ground and put the positive into each of the six pins, only getting signal on the center pin (supposedly the shared ground). Putting the voltmeter ground in the center pin and the positive on the others showed nothing.

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Or could I used my hacked 1/8"-stereo-to-speaker-wire adapter to send input to the amp? Could I hurt anything by sending audio down the ground, amp sense line, or other weirdness?

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No, I'm not integrating an empeg alongside the stock radio, sadly. I'm going to put a source switcher in for iPod aux in. I think it'll be a cool stealth install for my sister who doesn't care about audio quality; only wants to keep her brick totally stock.

<Depending on how rushed you are I could try to take a look in some local shops, the 240 isn't exactly uncommon here (but I'm still not allowed to drive so it's a bit of a project getting around ).

But I'll see if I can find something more detailed online though.

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Unfortunately, "AC V" and "DC A" settings on my unpowered analog voltmeter didn't show me anything coming out of the stock radio. With volume high or low, balance and fader centered or to one side, I saw nothing. What type of signal is line level output?

Sound shaped (i.e. AC), voltage (RMS or peak I don't recall) of between 1 and 8V depending on the radio (later/high end models often have the higher voltages as it allows one to run the amps on lower gain, reducing the influence of any noise picked up in the RCA wires (higher Signal/Moise ratio).

Of course, for a factory system most bets are off

Input resistance of amps are normally somewhere in the kOhm range so currents aren't very high.

You should get something on a low AC voltage setting (what's the lowest on your meter?), preferably having the volume on the radio turned up high and playing a steady test note.

What's the input resistance of the meter for voltage? If too low (unlikely, but with factory systems, who knows) it might overwhelm the current capacity of the output. Might want to try another meter, see if someone has one has one you could borrow - otherwise, new ones (digital) of OK quality (for general poking about activities) can be found quite cheap.

Unless of course the system does wacky stuff like only put outs the signal if it senses current draw on the remote or something like that. Never seen it, but factory systems...