Installing Thermometer And Voltage Monitor In A 4.2 D4D

July 17, 2011

I'm at it again. :yahoo: When I installed an aftermarked head unit, I lost my thermometer. I got a cheap one that matches the red instrument lighting pretty good. It also has inside temperature and a voltage monitor. Nice to have with an inverter in the back!

The thing runs on batteries, but for the illumination and volage monitor to work, a cigarette lighter plug has to be connected. I was thinking of hooking this up to something that gives +12v when I turn on my instrument lights. I looked through the 58 page wiring diagram but I can't make heads or tails of it. I tried most of the wires on the driver side junction box with a voltmeter, but can't find one that changes from 0 to 12v when I turn on the instrumt ligting. My initial idea was to place the monitor in the middle of the dash and run the wires down between the dash and head unit trim. The head unit buttons also lights up with the rest of the instruments, so I guess this means I can connect it to one of the wires that goes to the head unit?

And another thing; where would be a good position for the external temperature sensor? :g: When I removed the factory head unit I was left with a few spare connectors that didn't fit. I suspect they are for temperature sensor and something to do with fuel consumption as these are the features I lost. Should I be able to connect the new thermometer temperature sensor wires to one of wires on the spare connectors?

July 17, 2011

haha - I'll be watching this having taken the whole dash out of number 1 RAV. Not sure what I'll put back in !!

July 25, 2011

......but can't find one that changes from 0 to 12v when I turn on the instrumt ligting. My initial idea was to place the monitor in the middle of the dash....

If you're putting it in the middle of the dash, hopefully the old Toyota headunit had a connector into it like this:

The illumination signal is on R3, pin 17

I don't suppose for one moment the illumination on your new unit draws excessive amounts of current, but just put an ammeter in series and check. The illum signal is off the panel fuse (about 7.5A). Hopefully the slightly extra load won't tip it over the edge (it shouldn't).

And another thing; where would be a good position for the external temperature sensor?

I think the Toyota one is down behind the front bumper on the left-hand side, but could be wrong. It all depends on whether your new sensor is up to taking the environment conditions down there. I know of other makes that have placed sensors on the bottom of the wing mirror. They all suffer when they get "heat soaked" though. i.e. if been standing in the sun, they read high until the vehicle has been moving for a few minutes.

Should I be able to connect the new thermometer temperature sensor wires to one of wires on the spare connectors?

Not sure what you mean. It all depends on what sensor your new unit uses. There are simple thermistor ones or silicon based ones for starters. Even if it is a thermistor based thing, they can have a whole range of different characteristic curves and so there is no guarantee the existing sensor would give sensible temperature reading with your new unit (If that is what you mean of course).

July 26, 2011

Excellent info! The plug looks a lot like the main one for the head unit. When the weather clears up and I get the time, I'll take it out and have a look back there again.

I guess I'll also have to take a look at the front or underside of the car to find a suitable place for the temperature sensor. You understood me right, but I'll just put in the new sensor instead of tapping into the one that's already there. I hate it when the thermometer shoots up when the car is still. My RAV didn't do this, but I've had other cars with more sensitive thermometers. I guess I'll be looking for shade and not close to radiator or anything else that gets hot. Should I be worried about water with these sensors? I have no idea what kind of sensor it is, but here's what it looks like:

July 26, 2011

Should I be worried about water with these sensors? I have no idea what kind of sensor it is, but here's what it looks like:

Sorry, really can't tell what type from that. It doesn't look like too much care has been taken with it from an environment (water etc) point of view, but, well, who knows. Give it a go and prove me wrong :thumbsup: