96 Ex - new stereo install, ignition noise while running

[manimal]

Recently installed a cheap MP3/bluetooth head unit in the 96 which has factory "premium sound" amplifier, but no subwoofer - this same head unit model has worked great in the 91 that I gave to the MIL, which also had factory premium sound but /w woofer.

I purchased the Metra 70-5600 harness adapter. This adapter has two individual grounds, one head unit ground on the power adapter, and one AMP GND on the speaker/amp adapter.

I connected both the head unit and AMP GND grounds to the same primary ground from the factory harness - I assume that this is correct. Maybe not. I have not tried separating the two yet.

I then wired the AMP ON V+ wire to the "Power Antenna V+" wire on the head unit harness - this ensures that the amp is only turned on when the head unit is activated, rather than always on whenever the ignition key is in the ACC/RUN position. Again maybe this is incorrect - I do not know if the factory amp is supposed to be on whenever the key is in the RUN position - but I know that I tried this once and it generated noise on the speakers even with the stereo off, though barely audible.

Wiring splice between head unit harness and factory harness adapter is extremely solid using 16ga butt connectors

This same wiring setup worked great in the 91 and had no noticeable audio noise.

Unfortunately the 96 has ignition noise whenever the stereo is turned on in RUN position. In addition the noise changes with engine revs, indicating that the system is picking up noise primarily from the ignition system.

There is NO NOISE when running the stereo in the ACC ONLY key position - i.e. when none of the vehicle ignition or fuel systems are receiving power.

I've checked the following:

- Noise filter cap on ign coil is still present and connected.
- Hood is properly grounded.
- Ignition wires (Bosch) are brand new, replaced several months back.
- Have tried adding an additional ground wire from the harness adapter ground pigtail (including the AMP GND) to the steel support frame of the dashboard
- Tried grounding head unit case to the steel support frame of the dashboard
- Wiggled/checked every connector in the harness adapter
- Tried connecting an identical head unit to the vehicle - it shows the same symptoms.

I was going to perform an identical install on my dad's 2000, but until I figure out the noise issues with my 96, I would like to hold off on that.


Any ideas what to check next?

 

[malohnes]

Match your grounds from all audio components if at all possible. Multiple grounds can cause this sound whine/hum. So can weakly grounded ground wires or ground wires to thin of gauge. Lastly, many inexpensive components are so poorly made and engineered that they do this no matter how well installed.

 

[Kurantt]

When you say cheap cd head, do you mean it was not high level model, or is it a brand you have never heard of? Some of the off brand radios filtering is very poor, then you are running it into an amp magnifying any noise. try another head, or bypass your OEM amp. I had the same setup on my 96 with a pioneer head and had almost 0 noise. I could hear a little if you paused a cd and turned the vol up all the way, but it could not be heard over the music.