Gentlemen (& ladies),
This board has already been a great help. Im hoping someone can advise me on my first hiccup. I know this topic has been beat to death, but I just cant find the solution in any of the topics already on the forums. If im missing it, I apologize ahead of time.
My disco has the factory pioneer head unit with the CD changer under the seat. I purchased a new head unit with dual RCA's and this (link) harness adapter. The adapter bypasses the new heads speaker connections and it runs through the RCA's. Everything connected as it should. I get power to the unit and all speakers seem to work (though I seem to only have control over the center channel) However, with the vehicle in the accessory position I get a faint hum through the speakers. When the engine is started It gets pretty Loud. The headlights further increase the noise and it fluctuates with engine revs. In other words Im getting quite a bit of interference.

Has anyone had success installing a new head unit without rewiring the whole truck?

I plan on removing the head and redoing my harness wiring. Should I draw a new ground from the head unit to the chassis? I noticed the changer still has power. Should i kill the power to it? Im just trying to avoid a complete rewire and keep using the factory amps. Also as a side note, the factory unit worked without any issues or noise. I just wanted something a little more up to date with an AUX in.
Any advice is appreciated. Anyone who has had success with this, it would be great if you could chime in with your solutions. Thanks again for this forum!

 

that is a ground loop. It occures when you have two pieces of audio equipment getting power from different places (your cd player and your radio). You need to interconnect the two grounds. If they are grounded at different places the ground difference will travel through the audio cable making a buzz sound. New ground together to good metal=all good.....if that is how its wired. If not, let me know the wiring and we will figure it out. It IS a ground issue though.

 

Excellent. I was suspect of that so Ill give it a shot this weekend.
So I already have the new ground cable married with the old ...should I trace it and reground the whole thing to fresh metal? Can I just run the ground from the new head unit to adjacent area and leave the factory ground wire hanging or marry them, then split to fresh ground? I cant seem to visualize the loop in my head. Perhaps sleep will help lol.

I appreciate the quick reply

 

are you even using the cd changer? what could be happening is that the changer may have speaker outputs to the amp, so does the radio? If so the changers ground can send that back feed through the speaker wires and interfere, since you say it is on. Also, how did you "marry" the cable? I recommend first, no break in the wire to the ground, second option is solder splicing, and lastly, not twisting the wires together. The goal is to have as little resistance as possible to the ground. How is this wired to the changer, or is it? If you are not using the changer, kill the power to it before doing anything else, you have an excellent chance of solving your issue right there. hope this helps!

Also, I looked at you adapter, if what is above doesnt solve your issue, you will need to start troubleshooting. Connect a speaker directly to the back of the radio and see if it buzzes through that speaker. If it does not, then you may have an amp issue of some sort. then check all connections on that adapter, it may have a loose rca end. I don't think that is it though. You may even have to add a second ground wire for the radio. We will cross that bridge when we get to it!

 

Ok, I really appreciate your help on this. Ill try to describe how I have wired the best I can.

First off, The stock changer is not connected to the new head unit. To be honest I didnt even know it was there until I pulled out the stock unit and saw it's connection. I figured it received it's power from the deck, but it has its own feed. I'll have to investigate where and check out it's connections.
Next-- I connected the ground from the new head unit to the harness adapter with a wire nut. That plugged into the original system wiring. In order to connect the decks ground with the harness, I had to clip off a screw ground connector (looks like a flat tuning fork to be placed under screw on chassis) and then wire that to the ground on the harness adapter. That is where my question comes in. Should I have just ran the ground on the new deck straight to the chassis rather than connecting it to the harness adapter? If I did that, would I have an incomplete circuit by leaving the factory ground wiring disconnected? Also you mentioned not twisting wires, do you mean tangles, or where two wires connect in a wire nut?

Thanks again

 

no, a ground that has nothing connected to it can not affect anything, its just dead wire connected to the frame somewhere. I would try grounding yourself without going through the harness. As far as twisting wires, I mean dont take two bare ends and just twist them together, like you did when you put the wiring nut on. . It's probably fine, but not optimal. You can leave that alone for now.

1. I would ground the radio directly to the truck, not through harness, and remove any doubt there.
2. Kill power to cd changer
3. test
4. if still a buzz, test with a speaker directly connected to back of radio.
5. let me know

 

just run a new wire from the black ground wire (on the aftermarket harness) down to the edge of the carpet under the glove box (the closest floor to the radio) pull back the carpet until the metal floor is exposed and scratch a clean spot in it, then tap your ground there. It does not matter if the factory ground is attached or not. the factory radio (the one in dash) did not have an amp in it therefor it did not draw very much power, however your aftermarket amp does and it is drawing more power, too much for the factory ground in fact. think about it this way how do you think it would sound if you replaced your stock amp with say a 500 watt aftermarket amp but used the same(power,ground,and speaker wires) factory wiring?same thing goes for the in dash radio your aftermarket ground wire is probably twice the size (AWG) as your factory ground wire.

as for the factory cd changer reach under the seat and unplug it.

 

I did not see any mention of an aftermarket amp, just head unit, right? And why would you hook the ground through the aftermarket harness? I think that the harness connects his radio to the existing system, so the harness connects it to the old grounding system, and would defeat what we are both saying about a fresh ground.

 

I meant the aftermarket head unit has an amp in it, saying it draws quite a bit more current than the stock non amplified head unit. and yes a new ground is what he needs. and what I meant by aftermarket harness is the actual radio harness (the one that plugs into his aftermarket radio) not the wiring harness that adapts the radio to the truck. I am sorry I should try to be more clear about these things.

make sure your ground is as short as possible, make it a clean ground right on the metal of the truck and not a crossbar or a bolt, scrape the paint away completely where you tap the ground. star washers and ring terminals will help keep the ground solid for a long time.

I removed my factory cd changer without removing the seat it is nice to have the extra space, I mounted my sub amp in its place.

 

I appreciate the advice gentlemen. I am off to get supplies and will be doing all of this in the morning. I will report back with what I find. Thanks again!