Outside Air LCD Question - PeachParts Mercedes-Benz Forum

85chedeng300D · #1 08-17-2010, 11:08 PM

I was able to find and buy an outside air LCD and a sensor cable out of a W124 from the wreking yard last weekend and I am thinking of wiring them on my W123 using 2 sensors to read and display both outside and inside temperatures using a switch and an MB ice-cube-relay. Has anybody done this? (I know...I know... it's such a simple little German designed gadget and yet here I am making it complicated....)

Well anyway, I just need some expert's inputs before I start doing this upgrade. Please stop me from wiring the LCD on 2 sensors for any reason you think that it's not going to work or worse... ruin the LCD.

I draw and attached a diagram on how I'm going to wire them and I need a consult to make sure that I'm doing the wiring right and it's going to work or stop me if it's not.

Thanks!

Jeremy5848 · #2 08-17-2010, 11:22 PM

Nice schematic. The relay really isn't necessary; you can use an SPDT switch to change from one sensor to the other, or a rotary switch to change between multiple sensors. The sensor is just a thermistor (a resistor genetically engineered to have a lot of sensitivity to changing temperatures). You will want to test the sensors at various temperatures to make sure they read the same or at least determine the error from one to another, shouldn't be much more than a degree or two. Others have stuffed the 124 readout into a 123 instrument cluster, using the spot originally designed for a "PRND2L" column shift display. If it doesn't fit, I have a 126 display that might work.

Jeremy

85chedeng300D · #3 08-17-2010, 11:36 PM

Quote:

Originally Posted by Jeremy5848

Nice schematic. The relay really isn't necessary; you can use an SPDT switch to change from one sensor to the other, or a rotary switch to change between multiple sensors. The sensor is just a thermistor (a resistor genetically engineered to have a lot of sensitivity to changing temperatures). You will want to test the sensors at various temperatures to make sure they read the same or at least determine the error from one to another, shouldn't be much more than a degree or two. Others have stuffed the 124 readout into a 123 instrument cluster, using the spot originally designed for a "PRND2L" column shift display. If it doesn't fit, I have a 126 display that might work.

Jeremy

Thanks Jeremy!

SPDT switch? will an MB antenna up and down switch work?

The reason I originally want to put the 2 sensors on a relay and use a rear dome light switch is I want to use MB switches that I can put to replace the speaker fader wheel at the center console.

I did a little research the the shorter W124 display fit's better than the w126's.

I knew an expert will chime in and I'm glad I posted this question. Thanks for pointing out that a relay is not necessary!

Jeremy5848 · #4 08-18-2010, 01:15 AM

Yes, an antenna switch will work. You will have to do a little surgery on the wood of the console to hold the switch. When you rescue an antenna switch from the junkyard, be sure to get the socket too. Hint: If you plug the switch into the socket they should charge you for just one part; if you put them on the counter separately you'll be charged for two items.

DeliveryValve · #5 08-18-2010, 02:36 PM

Just in case you haven't stumbled upon this thread.
http://www.peachparts.com/shopforum/showthread.php?t=251755

Doesn't really answer your question though, Jeremy's got that covered, but may help you out in wiring it.

Sounds like a cool project. May do the same if it works out.

.

85chedeng300D · #6 08-19-2010, 12:22 AM

Quote:

Originally Posted by Jeremy5848

Yes, an antenna switch will work. You will have to do a little surgery on the wood of the console to hold the switch. When you rescue an antenna switch from the junkyard, be sure to get the socket too. Hint: If you plug the switch into the socket they should charge you for just one part; if you put them on the counter separately you'll be charged for two items.

Thanks for the tip! About the center console wood to hold the switch, I think I already got that taken care of. I empited out and drilled a rear defogger switch and converted it into a socket to plug in my Ipod, and soon when I found a matching OAT sensor and an antenna switch, I'm going to move the socket into the glove box (that's where I always keep the Ipod when not in use anyway, so I don't have to plug-unplug the Ipod jack) and replace it with an antenna switch that will be my inside/outside temp selector switch.

85chedeng300D · #7 08-19-2010, 12:26 AM

Quote:

Originally Posted by DeliveryValve

Just in case you haven't stumbled upon this thread.
http://www.peachparts.com/shopforum/showthread.php?t=251755

Doesn't really answer your question though, Jeremy's got that covered, but may help you out in wiring it.

Sounds like a cool project. May do the same if it works out.

.

Thanks for the link! I'm sure it will guide me through the upgrade but not until I make another trip to the wreking yard and find an OAT sensor that will match the reading with the sensor that I have right now and an MB antenna switch. Anyway I already bookmarked the link for reference in the future.