alternator whine, ground loop problem, need help

[ahardb0dy]

Hello all, Just joined, not new to car Audio or doing my own installs, just having a problem I have never had before and have a question.

details about the truck and equipment I am using:

1993 Nissan Hardbody, king cab KA24E 2wd, Swapped alternator using a 125 amp from a Nissan Quest.

Audio:

Headunit - Alpine CDA-3986

Front amp - Orion 275SX

Sub amp - Precision Power 2200 running 4 ohm ( bought new by me way back !)

Kicker KX3 crossover

Zero noise 3 ( I think) rca's

front door speakers - Alpine 6.5 coax

subs - two 12" Kicker comp in a sealed box

amps & crossover grounded through a distribution block with 4 gauge running to the jump seat bolt which I replaced with a longer bolt so I could attach a short length of 4 gauge under the truck that runs to the frame.

Headunit grounded to the metal center support below the radio

Had the same exact setup using a Sony headunit and no alternator whine

power (4 gauge) runs down pass side, RCA's down the middle, ground stays in king cab area on drivers side

Switched to the Alpine ( that came with the truck when I bought it) because it has the USB input.

Whine occurs on all modes (Radio, CD, USB)

unplugged antenna whine still present

Discovered today when I removed the ground for the headunit, that the radio still was on, thought it was grounding through the antenna, unplugged the antenna, radio still on, unplugged the RCA cables, radio still on, than realized the radio must be grounding through the radio kit which is metal, removed the 4 screws and pulled the headunit out and it finally went off.

So I know it's not good to have multiple ground points and this is my second Nissan Hardbody, I had a 94 Nissan Pathfinder also, all headunits were grounded in the same place and never had whine before.

Don;t think the sleeve is correct for the alpine as the radio will not lock into it, I had to attach the radio to the sleeve using a short bolt on each side (bolts are not touching anything inside), system works fine other than the whine.

So how do I isolate the kit from the metal in the dash? I know I could get a plastic kit, but I never had to do that before.

Should I drill a hole in the floor and install a bolt for my amp/crossover ground instead of using the jump seat bolt? ( that is how my install was grounded in my first hardbody (an 87)

Need help, thanks for taking the time to read this.

[Nick Papenborg]

If you have spare rca cables you could try these. Does your wine go away when you hold your alpine in your hand? You could ground your radio trough a cable on the same spot as your amplifiers. You can also measure your power cables from your amp. Make a wire on the battery - and run that wire outside your car. Now measure volts between the wire and your amp ground. Wen your ground is good you should measure a max of 0,5 volts. I hope it helps you.

[ahardb0dy]

It's funny, if I'm parked and rev the engine I hardly ( or rarely) hear the whine, it's when I'm driving. Maybe the whine only occurs at higher rpm's?

It seems when I had the radio not mounted the whine was almost gone, but I stopped (went on a test drive) and put one mounting screw back in and the whine was back.

I think I'm going to make anew ground point for the amps and crossover using a bolt through the floor, I had it this way in my former 87 Nissan Hardbody and didn't have any noise, If that does not work I can run the headunit ground to the same spot. What I'm concerned with is the radio grounding through the 4 mounting screws of the kit as it is a metal kit, may have to replace it with a plastic one.

Thanks

[RooTxBeeR]

It's funny, if I'm parked and rev the engine I hardly ( or rarely) hear the whine, it's when I'm driving. Maybe the whine only occurs at higher rpm's?

It seems when I had the radio not mounted the whine was almost gone, but I stopped (went on a test drive) and put one mounting screw back in and the whine was back.

I think I'm going to make anew ground point for the amps and crossover using a bolt through the floor, I had it this way in my former 87 Nissan Hardbody and didn't have any noise, If that does not work I can run the headunit ground to the same spot. What I'm concerned with is the radio grounding through the 4 mounting screws of the kit as it is a metal kit, may have to replace it with a plastic one.

Thanks

That does sound weird how you said after mounting the headunit it started. That might be the issue. Try to disconnect it again and see if it goes away right away.

[ahardb0dy]

I'll have to check my storage unit to see if I have a plastic kit, I already know the head unit is grounding through the mounts as well as the ground wire. I could tape the mounting "feet" but the metal screws would still complete the ground. May tape the mounting "feet" and just push it back into the dash and take it for a test drive.

Thanks

[3vil]

What about completely isolating the HU chassis? Wrap or tape it like you were saying, then use nylon hardware to screw it back in.

[ahardb0dy]

was thinking of plastic screws earlier, didn't know how well they would hold up.

Going to move the amp/crossover ground tomorrow to see what happens first I think

[ShadeTreeMechanic]

If the old radio was ok then it has to be a problem with the new one. Check the RCA out on the head unit with a meter to verify that the shield is still grounded to the chassis of the head unit. Some head units have a fuse on the ground internally and sometimes they blow. I would also abandon the ground wire in the harness and instead run a dedicated ground of 14ga from the radio harness straight to the battery ground. Also it would probably help to turn the gain down.

[ahardb0dy]

there is not a ground in the OEM harness on the NIssan. It wouldn't hurt to run the ground that far to the battery? Can I run the ground to the same point my amps and crossover are grounded to?

[ShadeTreeMechanic]

The amp ground point might be an ok place. Just have to try it and see. Check your RCAs and RCA ground too.