Previa stereo cuts out with other loads

[blankenship]

I installed a JVC stereo in my '95 Previa and have consistently been having it cut out, throw distortion/static through speakers, and displays a "Miswiring" fault on the display *when the car is running and I apply another load* (like touch brake pedal, turn on headlights, etc).


This does *not* happen when just playing the stereo off battery only, without the car running.
I had the alternator checked yesterday, and AutoZone said it was fine under load.
I've checked and rechecked the wires for the Metris 70-1761 aftermarket adapter, with my stock 9-speaker/sub system and all appears in order.


The Red "Constant" wire reads a constant 12.85V when on battery only, and rises to 14.66 with the car running.
The Gray "Switched Power" wire reads .62V when off, 11.62 when on battery only, and varies from 13.5-14.4V with the car running and various loads.
The Brown "Ground" wire seems consistent.


I've had this stereo in and out of the dash multiple times, and am so baffled.
Would love advice!

[man_btc]

IMO the likeliest culprit is a bad ground. I don't know what you mean by the brown ground wire being "consistent." Typically brown is for a dimmer connection or even a speaker, whereas the black wire is meant to be ground. Double/triple check the wire-color connections - if that doesn't turn something up, then it's a process of elimination - seeing what the resistance between the car chassis (ground) and the ground at the connector is when things are off, seeing if the "ground" voltage at the connector stays the same when things are powered, maybe even running battery power and ground direct to the radio to bypass the harness, etc.

[blankenship]

Thanks for that input re: Ground -
But the Haynes diagram the 12Volt (https://www.the12volt.com/installbay/stereodetail/2116.html) site both confirm that in the stereo harness Brown is the ground wire.
It's the wire I used to ground my voltage tester for all the readings in my previous post, so that's kinda what I meant by it being 'consistent.'

Does that change your instinct?
You're suggesting confirm resistance between that Brown wire ground and a known chassis/battery ground is between 0-5 ohms or so?

[man_btc]

You are correct, the brown wire in the Previa harness is ground - I was thinking of the colors I've seen on modern radio-side harnesses. where it's black.

On my '92 I measured about half an ohm between that wire and ground (my not-yet-repaired exposed windshield frame). I understand that to be typical (obviously use your meter on the lowest ohm setting, like 200 ohms).

You're saying that with the brake pedal on or the headlights on and the engine off, there's no problem? With the key either in the ACC position or the ON (Ignition) position?

[man_btc]

This may be more "data dump" than helpful advice, but...here's a copy of someone's notes and photos for a '95 sound system install (from poster "p_revia95" on the now-defunct Yahoo Group) plus a color wiring diagram for a '92 with a separate amp from when I bought a short-term subscription to the Toyota service doc site and was foraging and downloading like mad.

Also, poking around (as I'm sure you have) I ran across a mention of speaker distortion causing a "miswiring" message when the coil moves so much that it momentarily shorts to the speaker housing, so "miswiring" per se looks to be more consequence rather than cause.

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