1988 Pajero 2.5TD Outside Inside Thermometer Repair

[Craig Williams]

Gauge removed and connected to a spare battery I had in my shed.

Removed thermistor from front bumper bar (passenger, LHS) and used it to measure the inside temperature (which are the Red and Red/White wires at the back of the gauge, these can be seen in the fourth photo)

and then tested the outside temperature (you can see the thermistor in this picture which has some spare "speaker wires" running from it into the back of the gauge to the Black and Black/White wires)

Note there is a 3 degree difference between both temperatures even though both were measured at the same spot and the same time, my work shed. The readings should be the same but as the gauge is almost 30 years old there is some inaccuracy.
A view from behind showing how the wires are connected. Note: Blue/White wire to positive terminal and Black/Green is negative and the Black and Black/White going to the thermistor

A close up of the light blue coloured worn out 62 ohm 2 Watt resistor in the bottom left corner (it was very hot and working intermittently). If you touched it with the plastic handle of a screw driver it went off, and if you tapped on the front of the gauge it would start working again. If you look close you can see the "burn" marks from where it has been over-heating.

Will be continued on my next post....stayed tuned as the replacement resistor is still coming as its "in the post"

[Craig Williams]

3/06/17 a month later... the 62 ohm 2 Watt resistor arrived from China this week (in fact I made a mistake and ordered too many, so I have 39 spares! PM if you need me to post you one or two for a spare).

the bottom left corner has the new blue resistor soldered in place (it gets very hot to touch, leave a small "air gap" of say 2mm underneath it when you solder it back in place to keep it's heat off the PCB). I placed the old one underneath it just for this photo.
The small white resistor? immediately above the new blue one I just replaced was loose so I re-soldered it as well (check by gently wobbling each component using small long nose pliers and re-solder any loose ones)
Below is my wiring diagram which I used to work all this out

The gauge is now back in my Pajero Gen 1 and working perfectly, not bad for a 29 yr old gauge! Feel free to PM me if you have any questions

[1989pajero]

I will be doing this repair soon and thanks for the detail of your posts. you should be able to use a 62 ohm 5 watt resistor instead of a 2 watt right? I do not have one handy to compare but if the size will fit it should be able to work with less heat and prevent further heat damage.

[Craig Williams]

Probably will work if not too long or fat, otherwise I can post you one or two as I have 39 of them left over

[1989pajero]

Thanks for the offer but I live in the states so i am sure the shipping would be more than the resistor is worth.

[Craig Williams]

Recently the IOTG stopped working again, it was the top component, a diode in this photo

which had a dry joint which means re-solder to make a good connection.
So I have had three dry joints, see photo (and I had already replaced the 62 ohm resistor the big blue one at the bottom, prior to this. It gets very hot, don't touch it!).
My first post goes back to 1/11/14 almost 3 years ago now and it is still working (after a few interventions). Don't worry about the "-E" for error reading as I had not plugged in the thermistors!