XPost: alt.home.repair

Addressed especially to Clare and to anyone who thinks he's as smart as
Clare is.

Here is the wiring diagram for this car, https://www.dropbox.com/s/xoj71v8wiwwqtd7/Solara-Clock.odg?dl=0
It's an odg file, that LibreOffice Draw creates. I think most people
have programs that can display it, or the notes below have almost all
the same information.

I made an understandable but mistaken assumption in my first posts about
this, so let's forget about them and let me ask the question correctly:

The instruments above my car radio on a 2005 Toyota Solara can't be seen
in the daytime, unless the sun shines in directly through the rear
window, but they are illuminated when it's dark out. The illumination is
fine and they are easy to read.

I want to read them in the daytime too!


The instrument unit includes
1 Trip Monitor (MPG, Avg MPG, DTE, avg MPH, ET)
2 Clock
3 Outdoor Temp
Passenger present but seat belt not on - light.

From now on I'll call this whole thing the Clock.

1 and 2 light up with ignition in ACC and ON, 3 lights up in ON, but in
all cases, only if it's dark out.
This is true when the headlight switch is in the Auto position or any
other position such as Parking light, Headlight, or OFF.

What misled me before is that I've observed and the wiring diagram
agrees that when it gets dark, a photocell signals the Body ECU which
closes the Taillight relay and that sends power to the taillights and
the Panel fuse, and the Panel fuse powers lights in the speedometer
cluster, radio buttons, AC buttons, seat heater switches, gear shift
indicator and the glove box.

I mistakenly assumed that since those lights go on at night, the Clock
lights go on for the same reason. But in fact, the Clock lights go on
in the dark even if the Panel fuse has been removed, and they don't go
on in the daytime even if the Panel fuse has been bypassed to a source
that is 12V whenever the car is running, even in the daytime, and when
doing that has made all those other lights go on all the time that
normally go on only at night.

So am I to believe there are two separate mechanisms for turning on
lights at night? Why would they do that, and what would be the other mechanism?

BTW, if I use a dark-colored multi-layer rag to cover the light sensor
in the dashboard, I will trick the headlights into going on in the day
time. It takes 4 or 5 seconds for them to go on, and then about the
same for them to go off when I remove the rag. But doing this doesn't
make the Clock lights go on. But night time does make the clock lights
go on. What makes the car think it's night if covering the light
sensor didn't do that? WHAT ELSE COULD THERE BE?


So I looked in detail at the Clock. It's supplied by 5, count 'em,
five, fuses. Pins 7, 15, 16, 17, 22

7 comes from the IGN fuse, 12v when engine running
15 comes from the Panel fuse, 12v when it's dark out
16 comes from the Gauge1 fuse, 12v when ignition sw. is ON
17 comes from the ECU ACC fuse, 12v when key in ACC or ON
22 comes from the Dome fuse, always 12v,

All the pins are described next. Pin 6 seems hard to understand.

Pin 6. TAU terminal on the clock. Goes to Injector No. 1 WHY? Why
does it have input from the Injector. To calculate MPG, really? Even
though it has input on 5 labeled Fuel and on 12 labeled Speed. So why? Certainly not to tell the clock when it's dark out.


Label Color Conn. Function
1 GND1 W-B
2 TH- B-W IG6 AC ambient temp sensor (near front bumper)
3 TH+ G-R IG6 return from 2
4 SW 1 R Steering wheel display-control, and on to ground
5 FUEL LG-R to speedo cluster, fuel gauge, used for mpg display
6 TAU L IM2 to Injector No. 1 WHY? Why does it have input
from the Injector. For MPG? but it has input from 5-Fuel and
12-Speed.
7 TAUB B-R IM2 return from Injector No. 1 and also to IGN FUSE, 12v
when engine running
8 TBD L-B airbag sensor, 1
9 TX-1 W-B **but doesn't appy to my car
10 TX-2 W-B same as 1 for some reason
11 PBEW L-R airbag sensor, 2
12 SPD V-W to speedometer, used I'm sure for mpg display
13 DATA G-Y IK1 WHY? to TAM A11(A) A/C Control Assembly. So does
TAM mean Temperature AMbient? I guess so, since the AC page shows just
this part of the clock including pins 2 and 3 (the ambient temperature
sensor), and since the instrument 3 in the list at the top is the
outdoor temperature.
14 P-AB V airbag sensor, 3
15 TAIL G to Panel FUSE, but light goes on at night even when
Panel fuse is missing, and doesn't go on in day-time, even when
Taillight relay is bypassed and Panel Fuse is energized.
16 IG R-L to Gauge1 FUSE, 12v when ign. sw. ON, powers the
pass. seat belt warning light and much other stuff, only have 2006
list.)
17 ACC Gr to ECU ACC FUSE, 12v when key in ACC or ON (also headlights, fog light, speedo meter, power mirror, AUTO LIGHT CONTROL)
18 ILL- W-G to speedo cluster (combination meter)
19 TAMO LG-R to skid control ECU. What does this have to do with
any of the 3 gauges in the clock?
22 B+ R from Dome FUSE, always 12v, needed to keep clock
running all the time (also dome light, fob receiver, garage door
opener)


But does any of this show how the lights in the Clock are on at night
and not on during the day?


(Part of the reason it's taken so long to ask this question is that some testing can only be done at night and some only int

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