So I installed an aftermarket Pioneer stereo (50 watts per channel) in my 88 Fiero GT, and I ran into a couple of things I'm a little unsure of. I bought the wire harness installation kit designed for GM cars from this era to make it easier and wired it up per the instructions and what not. I have done this several times over the years with a lot of different cars and did not expect to have any issues.

The first thing I noticed is there are two harness. The main harness and a little two wire harness. The little two wire harness has an orange dimmer wire that I'm not sure where to hook up. The only other orange wire is out of the other harness, but if I hook them together it would bypass the aftermarket stereo all together as there is no wire from the stereo for them. In any case, I left them unconnected and the stereo seems to work fine. What are they for and is it ok to leave them unconnected to anything?

Now for the bigger problem. The aftermarket stereo did not like the factory amp. ALL of the speakers were bass saturated and sounded horrible. I turned up the built in High Pass Filter to the highest setting and the four regular speakers sounded a lot better, but the aftermarket 200 watt 5.25" PYLE subwoofer was almost non-existent. The slider was all the way to the left, so I pushed it to the right about 20% of the way and the sub goes to a straight bass tone that will not go away until you turn the radio off. I have read all of the forums on here concerning the factory amp, and I checked the wiring per the info provided in them. It is all hooked up correctly. The only thing I can think of is the Pioneer has subwoofer out connections that I did not use. Do I need to connect these to the amp for the sub? Do I need to wire the other speakers directly to the radio and bypass the factory amp? Any suggestions/advice would be greatly appreciated!

The two wire harness is constant +12volts and the dimmer, dimmer is brown. if you have an amp you should always use the pre amp outputs, better sound quality.
Short response, but I hope it helps.

does your car have the factory subwoofer setup

Yes, it does.

quote Originally posted by Perk: So I installed an aftermarket Pioneer stereo (50 watts per channel) in my 88 Fiero GT,

What model# is the Pioneer Unit?

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My World of Wheels Winners (Click on links below)

3.4L Supercharged 87 GT and Super Duty 4 Indy #163

MVH-X370BT

quote Originally posted by Perk: Pioneer MVH-X370BT

This should help those of us trying to figure out where your wiring is crossed.

PDF of the Owner's Manual. Wiring connections on Page 16
https://www.pioneerelectron...nersManual060614.pdf

Normally, you would connect wires 6-13 to your 4 main speakers and run them off the deck's internal amp as in the first diagram.

Directions are a little confusing when you want to use a subwoofer INSTEAD of rear speakers.
It looks like you use 10,11 to power a single 4ohm subwoofer (no external amp).
Direction 19 is for running a single 2ohm subwoofer, and Direction 21 is for TWO 4ohm subwoofers.

If you want to run 4 speakers AND a subwoofer...
The deck has RCA outputs for running an external amp for a subwoofer.
But I think the factory subwoofer amp is expecting speaker level inputs, so RCA signals may be too weak a signal.

I'm not sure how you could boost that signal, or how you'd wire it to the factory subwoofer amp.
Maybe someone else has an idea on that.

[This message has been edited by fierosound (edited 10-28-2015).]

Thanks for the help! I'll look further into it this weekend. I wonder if anybody has a schematic or wiring diagram of the amp itself?

quote Originally posted by Perk: Thanks for the help! I'll look further into it this weekend. I wonder if anybody has a schematic or wiring diagram of the amp itself?

I think this is it - from this thread
https://www.fiero.nl/forum/A...100421-2-083145.html

NOTE: The speakers are powered by the radio itself. The factory amp ONLY runs the subwoofer.

[This message has been edited by fierosound (edited 10-28-2015).]

So I cut all of the speaker wires going to the amp except the wires going to the sub, and all four main speakers sounded great. I moved on to the sub using the subwoofer RCA outs. At first I hooked up the right rear to just the right RCA, but you couldn't really hear the sub even at high volumes. So I hooked up the left rear to the left RCA, and you could hear the sub but not as you should at corresponding volumes. I went ahead and hooked up the left front and rear speaker wires going to the amp to the left RCA and vice versa for the right. At first it sounded great, but as soon as you turn the volume up high enough for the sub to really produce, it went to a solid/wavering/stuttering bass tone. The same issue I had before. I managed to mess with the settings on the head unit to get it sounding good at semi-loud volumes, and I think that is the best it is going to get.

I think in the future my best bet is to get an aftermarket amp for the sub. For now, this will have to do.

Thank you to those that provided input to help me out.

Not completely clear what you're doing..

Don't use the RCAs at all (low power output)
You will only use them if in the future you get an amp that uses RCA low power inputs.

The factory sub amp needs "speaker level" (high power) inputs (why you're not getting any volume).
Run 2 wires between +/- of 1 of the speakers to the +/- of the sub amp.
The amp has the x-over to tap the low frequencies and amplify them.

Speaker polarity on factory diagram is B+ A-

Example of what Cliff did (quoted earlier)

[This message has been edited by fierosound (edited 11-02-2015).]