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Discussion Starter · #1 ·
Hey all,

I recently installed the t1819 head unit out of a 2013 Scion. Everything hooked up easily enough with the harnesses bundled in PT546-00142 (Bundle includes: PT546-00120-CH, PT546-00120-AD, and PT546-00120-US).
But there’s an issue with the head unit lights. When I turn on the parking lights or head lights, the radio display turns off. The button illumination does not come on either.

Anyone else have this experience? Any insights? Thanks in advance.
 

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Does anything unusual happen to the A/C, Hazard, & Gauge illumination when you turn on the parking or head lights?
 

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Discussion Starter · #4 ·
Does anything unusual happen to the A/C, Hazard, & Gauge illumination when you turn on the parking or head lights?
The A/C, hazard, and gauge illumination all see to function normally with the parking and head lights switched on.
 

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Discussion Starter · #5 ·
Perhaps your instrument dimmer wheel is all the way down.
I know I'm pretty clueless, but I actually haven't been able to find where the dimmer wheel is located. Where is it located? Do all the models have one? The gauge illumination seems to work properly.
 

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While sitting in driving position put your left index finger in the useless coin holder, it should be the only dial which is adjacent to your finger (I forget if its just to the side or below). At least that's how I learned to find mine in the pitch black.
 

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Discussion Starter · #7 ·
While sitting in driving position put your left index finger in the useless coin holder, it should be the only dial which is adjacent to your finger (I forget if its just to the side or below). At least that's how I learned to find mine in the pitch black.
I’ll take a look. Thanks!
It’s a RHD JDM MR-S, by the way. I think the coin holder is on my right hand side, and next to it i thought was a blank. But I’ll check again.
 

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Discussion Starter · #8 ·
A Google search tells me that spyderchat user illadef had the same issue with the t1819 install back in 2009. But at that time, no one seemed to have an answer. I’ll update if I can figure out what’s going on.

 

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Discussion Starter · #9 ·
An update, in case there’s anyone else for whom this is of interest:

My MR-S does not have a gauge dimmer switch/wheel. Apparently, this feature wasn’t standard on many JDM cars of that age. I don’t even know if it was offered at all in the MR-S. Certainly, mine does not have it.
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I’ve tested the wiring from the vehicle harness going to the radio unit. And the illumination+ (green) and ground (brown) do read 12V when the parking lights or headlamps are switched on, and it reads 0V when lights switched off. So I think that part is in order.

I suspect the radio illumination issue is related to the absence of a dimming function in the car. But I haven’t quite figured out why.
 

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I’ve tested the wiring from the vehicle harness going to the radio unit. And the illumination+ (green) and ground (brown) do read 12V when the parking lights or headlamps are switched on, and it reads 0V when lights switched off. So I think that part is in order.
If both the green and brown wire have 12v, there is no voltage difference to power the radio illumination. Find out how the ground wire got 12v on it.
 

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Discussion Starter · #11 ·
If both the green and brown wire have 12v, there is no voltage difference to power the radio illumination. Find out how the ground wire got 12v on it.
I probably didn't put that very clearly. I meant there is 12V in the illumination+ (green) when parking lights are on, grounded to the brown wire, if that is any more clear.
 

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Discussion Starter · #12 ·
I'm not sure, but I think I'm getting closer to finding the problem.

As far as I've seen, the stock MR-S (JDM) only has the 10 pin connector, and not the smaller 6 pin connector going into the stock radio. In the USDM MR2 Spyder, there is the 10 pin connector and also the 6 pin connector. There are no rear speakers in the spyder, but from what I've seen of others' USDM spyders on youtube/etc. the 6 pin connector is there and has just one wire in it. That wire appears to be in the 5th location (see T1819 pinout below).

I think this makes sense since the MR-S did not come standard with the dash dimming feature. And in my car at least, and other JDM MR-S I've seen in videos, there is no 6 pin connector present in the stock wiring harness to the radio.

In the Pioneer T1819 unit, that 5th location in the 6 pin connector is the illum - input. The illum + input is on the 10 pin connector. I don't have any wiring schematics for the T1819, but I wonder if omitting the illum - input is what is causing the unit to behave the way it does. It's very specific. There is no backlight to the radio buttons. And when the headlights go on, the digital display blacks out. No backlight illumination happens.

This from a thread about the Scion FRS T1819 install back in 2015:
These directions are very good; just remember there is a small 6 pin plug that originates from the MR2 which will go directly into the OEM radio (I did not remember this). Oh, and the 8 screws holding the radio and cup holder to the vertical bracket needed an impact wrench to come loose. Stereo looks and sounds great too, but $150 for OEM wires is too much Toyota . Good luck.
So, my next step is to get a hold of the 6 pin connector and try connecting that illumination neg input to ground. See what happens.

Thanks for the suggestions and ideas so far. If anyone sees something I'm still missing, please fill me in.

This is from yoursciontc forums:

T1819 radio connectors:
10pin connector:
1 -> front right +
2 -> front left +
3 -> ACC ignition +12V
4 -> battery +12V
5 -> front right -
6 -> front left -
7 -> ground
8 -> (antenna amplifier + output) now on antenna connector, you have to splice in here
9 -> amplifier control + output
10 -> illumination + input

6pin connector:
1 -> rear right +
2 -> rear left +
3 -> rear right -
4 -> telefone mute input, connect to ground to mute radio
5 -> illumination - input, connect to ground if not connected to rheostat (instrument illumination dimmer)
6 -> rear left -
 

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Discussion Starter · #13 ·
So my suspicion was correct. Once I connected that 5th pin in the 6 pin connector to ground, all the back light started working properly.

Issue resolved. Again, thanks to all of you who helped with input and suggestions.
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