Temp display help! - PeachParts Mercedes-Benz Forum

C Holmes · #1 05-19-2009, 08:05 PM

Hi, Anyone know if it is possible to install a 5 pin temp display into a four pin harness? I have a 300 TDT and would like to put the newer version in. I can get it to work no problem but when the lights are turned on it goes blank. I can put power to the last pin which seems to be the light but it will also blank out the display. Any ideas around this? Indecently if I unplug the rheostat it is fine but also no illumination but also no switch or CCU illumination. I KNOW someone smarter than me has figured this out so please share!

Jeremy5848 · #2 05-19-2009, 08:14 PM

This question was just answered here a few days ago . . . here. All you had to do was scroll down a bit or use the search function.

babymog · #3 05-19-2009, 08:42 PM

You have the display grounded to the instrument lights.

The 5th/new pin is speed input, the terminal block directly forward of the tachometer under the dash.

C Holmes · #4 06-11-2009, 06:44 PM

why does the temp display have a speed input?

Jeremy5848 · #5 06-11-2009, 11:16 PM

Quote:

Originally Posted by C Holmes

why does the temp display have a speed input?

It freezes the reading at low vehicle speeds/when the car is stopped in traffic, to keep the reading from going ridiculously high. For example, my '87 300D Turbo (W124, OM603) has the outside temp sender in the left end of the front bumper (later models moved it to the front by the license plate frame). On hot days when the thermostatic engine compartment vent opens and dumps hot air out the left side, the sensor gets bathed in hot air and the gauge spikes up above 110F even though the actual outside temp might be only in the 90s.

C Holmes · #6 06-12-2009, 04:56 PM

Clever! You know the Germans make good stuff. Now only if I could find someone to tell me how to wire four pin harness to the newer five pin readout.

Stevo · #7 06-12-2009, 05:33 PM

I would like too have a temp display in the cabin of my 240D. My Dodge truck has one and its kind of nice, anyone used an after market unit, or I could tape a thermometer to the outside of the windshield

Jeremy5848 · #8 06-13-2009, 01:16 AM

Quote:

Originally Posted by C Holmes

Clever! You know the Germans make good stuff. Now only if I could find someone to tell me how to wire four pin harness to the newer five pin readout.

Four pin harness === Five pin module
---------------- === ---------------
Power (black/red) === Pin 5 (black/violet or similar)
Ground (brown) === Pin 1 (brown)
Sensor (green) === Pin 3 (green)
Illumination (black) === Pin 2 (grey/blue)
----------------- === Pin 4 (speed sensor, not used)

Jeremy

C Holmes · #9 06-13-2009, 07:17 AM

Thanks, I will try that. I believe the brown on mine has two wires to it.