harness to wire in aftermarket stereo (Part # inside)

[monterey1962]

Just installed a Pioneer head unit into a '91 LTC successfully without rewiring all the speakers.

I used Metra brand wiring harness Part #70-5510.

The wiring for the speakers is easy as can be since it uses the pre-amp outputs. The harness for power and such went as follows.

Position 1: Constant (+), this one was a correct color match.
Position 2: Ground (-), this one was not a correct color match, however, it IS the factory ground wire and should be used for ground.
Position 3: Key on (+), this one was also correct.

I didn't use any of the display/dim wires since the Pioneer unit did not have any to match with the harness.

The blue "amp signal wire" from the aftermarket head unit needs to be wired to the blue wire on the Metra harness to activate the factory amp.

If you have an LTC with auto-antenna, you need connect the blue "amp signal wire" from the aftermarket head unit to the blue wire on the Metra harness to activate the factory amp AND the blue w/stripe wire on the Metra harness to activate the auto-antenna.

[87gtVIC]

That is a pretty cool harness if your radio has preamp outs.

What Pioneer radio did you install?

[monterey1962]

Can't recall the model number. Just got a pic. It's a very nice head unit. Similar to the one in my truck.

[tjc78]

That harness is a nice item. I like how you can still use the factory amp. I remember using an "amp bypass" cable in the trunk as the solution before.

[marquisman]

iv used scotche harness' before for premium sound cars. i never had issues with them.

[gadget73]

The harness Monty posted will actually use the factory amp though. I've wanted to try that setup out. I've also wanted to make a harness that goes the other way to allow use of an aftermarket amp in the trunk without fishing RCA cables through the car. No reason the factory signal wires won't do the job.

[marquisman]

the scotche one uses the stock amp too. its a grey flat power connector and a black small square connector that plugs into the speaker/amp side of the harness. iv used them in both my '91 mercs and one in my bros mark VII.

[tjc78]

The harness Monty posted will actually use the factory amp though. I've wanted to try that setup out. I've also wanted to make a harness that goes the other way to allow use of an aftermarket amp in the trunk without fishing RCA cables through the car. No reason the factory signal wires won't do the job.

I've done that for the speakers only. I took Crutchfield's amp bypass (I wonder if they still make it), cut it in half and created a harness to my amps in the trunk. It worked perfect, and I didn't have to cut a single wire in the car. Behind the dash, I only hooked up the power and ground to the radio but still had to run three set of RCAs (front, rear, sub) from the head to the trunk.

There is no reason you couldn't use the signal wires as well, you would have to solder on some RCA plugs at least at the amp end. On the head unit side you could cut off the RCA outs and hardwire it.

[gadget73]

the scotche one uses the stock amp too. its a grey flat power connector and a black small square connector that plugs into the speaker/amp side of the harness. iv used them in both my '91 mercs and one in my bros mark VII.

does it use the speaker connections on the aftermarket stereo, or the preamp connections? You really shoudln't feed speaker level power into the amp. It will tend to make it overload and/or burn up.

[marquisman]

maybe im talking about something else. here is a link to the harness i use. http://www.scosche.com/products/productID/248

[gadget73]

yeah thats speaker level output, not line level like an amp expects. It really ought to be fed off the RCA jacks so it doesn't overdrive the amp.