Help Car wont start after headunit install

[Brenner41]

2013 Scion frs
Old Headunit: Kenwood dnx6990HD
New Headunit: Atoto S7 XE
I recently got a new head unit and was installing it in my car, when I discovered that the previous owner had installed a radar detector (beltronics sti-r plus). It wasn't on and was all stashed behind the dash. It was an absolute rats nest with shawty wiring and I've taken it out. It was spliced into the wiring harness (the head unit wiring harness, not the main one). I have then reused the head unit wiring harness for my new head unit and butt connected all the appropriate wires. When I try to start the car I can get the key position to on but if a crank it all goes black and I lose power to everything and could not get power in any of the key positions afterward. I checked all the fuses and non were blown. By taking them in and out I was able to get power back in the key positions up to on. I am not sure what is wrong or where to check further. The head unit works fine and dims and everything with the lights and plays music to all speakers. Looking for some help, please. I looked online and couldn't find much.

[Tcoat]

First things first and not insulting your intelligence.
Have you checked battery power level?

[Brenner41]

Ya battery power is fine 12.4V. I can't test if it's dropping voltage when I crank cuz it doesn't even crank. It shouldn't tho as the battery is only a year old.

[soundman98]

the cars not in gear, is it?

a number of past vehicles, the radio was easier to install with the shifter somewhere except 'park'

[Brenner41]

It a manual so no park but its in neutral.

[soundman98]

check the clutch switch?

[whataboutbob]

Disconnect the stereo, try to start. Go from there.

[soundman98]

i really doubt it's anything to do with the head unit itself. that's the specific reason i have the car. the hu has no real interaction with the rest of the vehicle. especially 2013-14.

it's got to be a battery, switch, fuses, or ecu issue.

you checked all fuses in all 3 fuse locations? on the battery, under the hood, and under the steering wheel?



the unknown concern here is the butchered wiring the previous owner modded...

[Trollhart]

Did you maybe rip off any grounding wire behind the dash?

[Brenner41]

OK, I have checked the fuses under the steering wheel and main fuse box. I'll check battery fuses and check the clutch switch after work.

The car has no power or at least no dash lights without the stereo installed. (I know this shouldn't be)

That's what I was wondering if I accidentally ripped out a ground but I'm not exactly sure where to check. I looked for any loose wires or disconnected ones and didn't see any. If you could point me where to check.



Thanks all for the suggestions. I can take videos or pictures if it would help.

[Brenner41]

I checked battery fuses and they were fine.

[soundman98]

Originally Posted by Brenner41

The car has no power or at least no dash lights without the stereo installed. (I know this shouldn't be)

That's what I was wondering if I accidentally ripped out a ground but I'm not exactly sure where to check. I looked for any loose wires or disconnected ones and didn't see any. If you could point me where to check.

this is a good first step.

i believe the radio is grounded via the mounting tabs. i had to ground my aftermarket radios separately to a different bolt because the plastic mounting kit got in the way of the metal chassis self-grounding itself.

so everything worked with the kenwood, was the only alteration to the wiring adapter kit?

i know it's next to impossible, but can you try to take a picture of the wiring harness you have with the wires splayed out enough to see each connection?

it might also be worth unplugging the radio and troubleshooting the car independently-- it's assumed that the new atoto radio is good, but it could also have an internal defect as well we're all overlooking...

[Trollhart]

Originally Posted by Brenner41

That's what I was wondering if I accidentally ripped out a ground but I'm not exactly sure where to check. I looked for any loose wires or disconnected ones and didn't see any. If you could point me where to check.

Can you try to start the car with a jumper pack? The battery might have developed a dead cell incidentally, this should be ruled out first.


If that does not solve the issue; it has been a while since I have been behind the dash, but there are several grounding terminals on the firewall. They can be seen most easily when the head unit is removed with as much of the aftermarket wiring harness.

The easiest one to reach is visible on the upper right side behind the head unit slot.

Removing the glove box will help to see/reach other ones as well.

FYI; I managed to rip out a ground without noticing when working on my rear view camera once, and was shocked how easy it was to just sever the thin cable.


In any case, the car *should* start just fine without a head unit, so if it does not, I believe you should further diagnose the issue in this "default state" without any aftermarket unit/harness connected.

As far as I have tested, there is absolutely no interaction between the OBD and the head unit in these cars.


Another thought: Do you have a wiring diagram for the Radar Detector? You said the wiring was shoddy, so there might have been some mysterious connection keeping the car alive?

Sadly I have no idea how these things are supposed to be wired, since Radar is not used in my country and any detection stuff is highly illegal anyway.

Assume it needs at least 12V power source and a ground (which might have been compromised during the removal)?

[Trollhart]

Originally Posted by soundman98

this is a good first step.

i believe the radio is grounded via the mounting tabs. i had to ground my aftermarket radios separately to a different bolt because the plastic mounting kit got in the way of the metal chassis self-grounding itself.

There is a ground pin present in the OEM wiring harness, which might or might not be utilized by the aftermarket harness.
My Pioneer unit is only grounded via the harness.