Rear Sound w/ Aftermarket Head Unit

[wf758]

My 1992 already had an aftermarket Alpine head unit in it. However, the controls on that unit mostly didn't work. I plugged in a brand new Alpine unit (I'm not sure what the original wiring should have looked like, but an existing Alpine harness is in place). I found that fading (using head unit controls) to the rear speakers identified that I'm getting only a very muted output from those speakers. Wondering if anyone has any ideas as to the cause? Thanks


1992 500E
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[gsxr]

The USA-spec factory stereo systems used from 1991-1993 USA model years (Becker 1432) are a funky setup with remote tuner in trunk, two separate power amps in the trunk, and a speaker-level fader in the center console.

When an aftermarket head unit is installed, it totally depends how the installer wired it up. My guess is that they did not wire the 4 speaker outputs from your Alpine to each of the 4 main speakers. I'd also wonder if they were able to get the front door midbasses working at all (possible, but not easy).

Did the rear speakers have normal volume levels with your previous Alpine head unit? If so, try fiddling with the console fader wheel to start with...

 

[maw1124]

That could literally be anything. Is there an amp with the head unit, or just head unit? Factory or replacement speakers? IIRC, the factory fronts are 2 Ohm, the rears 4 Ohm. My guess is either way you're looking at a rewire to get to the bottom of it. I can't imagine what you'd come up with trying to run an aftermarket head unit through the factory amps and speakers. I had my whole system rewired and though to most it sounds great, I'm still fiddling with it.

Apparently the factory came with a crossover between the front door and dash speakers, which crossover worked "well enough" with a 2 Ohm load. Now that everything is aftermarket (head unit, door and dash -- all 4 Ohm), a friend is custom fabricating a 4 Ohm crossover to run between the door and dash speakers. It's well within his area of expertise and well outside of mine...

So I've been a fair bit down this particular rabbit hole and am willing to help you through it. But it likely begins with rewiring that Alpine harness that's there. It's probably all wrong in ways you don't want to know, particularly if someone tried to "hunt and peck" to splice it into the factory setup and fader knob. My guys bypassed that knob on my instruction -- it was the only thing they came back to me and said "we don't know how to make this work, so what do you want to do?" And that was after removing the factory amps and what not -- I went with an aftermarket amp. My guess is trying to use an aftermarket head unit with the factory amps is all a fools errand -- endless hours and expertise, never a proper outcome.

Good luck.

maw

 

[gsxr]

I believe the dash speakers are 6 ohm, and the door speakers are 2 ohm. Aftermarket amps don't always play nice with these. The factory amps were designed for the odd impedance, and I suspect they also had some fixed EQ built in specifically for the 124 cabin, although I can't prove that. If you upgrade the dash speakers to aftermarket stuff at 4 ohms, this will affect the balance between drivers. Switching to aftermarket gear is not easy (if you want it to sound really good), unless you replace pretty much everything, which gets expensive fast.

Use an aftermarket head unit with the factory amps is only a problem on 1991-1993 cars with 1432 systems. It's a breeze on 1994-95 models (and 1990, the first year with outboard amps, and still using a 'normal' head unit).