outside temp indicator '87 w124?? - PeachParts Mercedes-Benz Forum

djankov · #1 01-19-2003, 02:20 PM

I bought a replacement LCD unit for the outside temperature display for my '87 300D. The old display was turning black. However, the new display has 5 inline pins labeled 1,2,3,4,5 where the old one has 4 pins (square 2 + 2) labeled 1,2,3,4. I figured the 5th pin on the new display was not needed, since the new part was listed as a replacement part for the original in the parts manual. After buying the new inline connector at the dealer (about $2), I wired 1-1, 2-2, 3-3, and 4-4 and all that comes on is the light, no temp indication (blank).

Any ideas?

'87 300D (178km)
'01 CLK 430 (21km)

#2 01-19-2003, 03:26 PM

My question is, where'd you buy the replacement LCD ?
I was told by the dealer that they only sell the whole cluster unit. I'm interested in getting the LCD too. !
thanks.

djankov · #3 01-19-2003, 03:43 PM

I bought the whole replacement unit that is held in place by the 2 screws in the instrument cluster. However the pin configuration is different.

#4 01-19-2003, 03:58 PM

Well, if you purchased it from the dealer then take it right back. The replacement configuration should be the same exact one.
good luck.

djankov · #5 01-19-2003, 04:32 PM

I got the part on ebay and got the additional connector from the dealer. The parts manual lists that this is the replacement part when combined with the additional connector.

However, no instructions.

md21722 · #6 01-19-2003, 11:41 PM

The LCD display was updated in later model 124 cars to include a wire from the hall effect (speed) sensor to enhance the accuracy of the system (which is unreliable at low/stop vehicle speeds). I'm not sure if the original part is still available.

You CAN use the new style IIRC - gsxr has the answer.
Wiring pin 5 to ground may work.

J.HIDALGO · #7 01-20-2003, 02:04 AM

Just disassemble the unit and exchange the LCD crystal. I disassembled mine while trying to find the problem with it. The LCD portion was also turning black.

#8 01-20-2003, 02:06 AM

Did u replace the crystal ?
where did you buy it and what's the reference number for that crystal ? More over who sells the crystal by itself ?
thanks.

J.HIDALGO · #9 01-20-2003, 02:16 AM

However, you can buy a used temperature indicator unit (even one that is not working) and just change the LCD crystal. As long as the crystal is still intact/gray. NOTE: this only applies if you LCD display still shows the correct temperature and the only problem is the LCD is turning black or dark.

gsxr · #10 01-29-2003, 10:19 PM

OK, guys, here's the scoop. Yes you can buy the LCD unit separately from the cluster. The dealer will happily sell it to you for some obscene amount like $300. I can dig up the part number if anyone REALLY wants it. The better method is to buy a used one at a salvage yard. Most of the major MB yards (Silver Star, PG Auto, etc) will sell them for ~$75. I just bought one from PGA for $75+s/h.

Pinout: The older models had 4 pins only and no connection to the Hall sensor. From about 1990 up, MB improved the design to eliminate false readings at low speeds. This unit has 5 pins and the extra pin is for the Hall effect sensor. You do not need to connect the 5th pin, it will act just like your old one did (you know, showing 120F at idle in summer when it's only 90F outside.) As to how to wire the 5-pin display to a 4-wire car, follow the schematics in this PDF file:

http://www.meimann.com/docs/mercedes/LCD_temp_testing.pdf

Can you add the signal from the Hall effect sensor to a car that originally came with a 4-wire display? I think so. I researched the parts used for the old & new cars, and my 1987 300D has the same Hall effect sender on the back of the speedo as the late 124's up to 1995. It looks like a matter of tapping into the Hall wiring and running a feed to the extra pin. I have NOT attempted this yet, but I plan to in the near future.

HTH,

djankov · #11 02-21-2003, 09:06 PM

OK, mine works now. However, you cannot connect the pins as I did originally. Here is the correct mapping that I figured out from gsxr's link above.
From the OLD 4 pin harness to the NEW 5 pin display:
1-5
2-1
3-3
4-2
and hall sensor to 4 (if available)

I only connected the first 4 and the temp works fine. According to the electrical diagram, the B6 Hall road sensor has 3 wires, but mine only had 2, so I didn't bother at this point. I mght revisit it later.

gsxr · #12 02-21-2003, 11:50 PM

I ordered all the parts that should allow me to connect the Hall sensor 5th wire to the new display. I expect them to arrive next week. If it all works, I'll post the part numbers needed for the pin sockets & connector bodies. If not, I'll post why not. Not sure how I can test the function, may have to stick a hair dryer on the sensor and see if the reading remains the same or something (shouldn't change when stopped if the Hall sensor feed is working). At least I think so.

richard28 · #13 10-27-2003, 12:29 PM

On the 87 300 model, would you confirm the temp sensor is behind the front license plate? I ask because on my 87 300e, there is nothing behind the license plate & the dash led is lit, but it is completely blank. However, there appears to be some kind of sensor on the driver's side front edge of the radiator, about half way up, in a little holder/bracket, & I thought this might be the sensor. The crystal is good because I swapped it out of a working sensor from a 91 300e. Thanks.
Richard

gsxr · #14 10-27-2003, 12:57 PM

Nope. On ealy 124's, the sensor is in the front bumper, on the left corner. It's embedded and you can only see a little hole on the bottom side of the impact strip where the tip peeks out. Very sneaky location. You access it from behind the bumper. On a diesel 87, it's very close to the oil cooler. On a 300E, it will be somewhere in there ahead of the left front tire. Later models had the sensor at the license place, IIRC. I simply re-routed mine there when I replaced the sender. You can add the Hall effect signal to a later model "5-wire" LCD to get the newfangled circuitry that helps provide more accurate readings, by not allowing the temp reading to skyrocket when idling in traffic:

http://www.meimann.com/docs/mercedes/LCD_temp_install.pdf

http://www.meimann.com/docs/mercedes/LCD_temp_testing.pdf

Worked great on my car!

TROVERMAN · #15 10-28-2003, 09:11 AM

I have a '95 E320 (w124) and when I purchased the screen lit and was clear, displaying either nothing or usually +136F. My sensor is behind the plate. I went to my local junk yard and found two 1985 300 series cars. They each had a little silver sensor behind the bumper with a wire coming from it. They didn't look the same, but I cut one and unmounted it. I got it for FREE! Back at home I cut mine, it had two wires in the sheath, a brown and a green. Spliced it together, and now it displays the accurate temp! Free Fix! My question is, why does the sensor on my 1995 with only 40k miles on it fail, and the one I get from the junkyard from a 1985 with 260k on it plus the interior fire that caused it to be in the junkyard work fine? Is it a sign of MB quality? I think my wagon is a Euro edition, though--clear lenses, white driving lights, wide Euro plate mount in the front--actually had to drill my license plate to get it to fit! The junk sensor said "Germany--+85 degrees Celesius, yet on my dash the display reads Fahrenheit. Did that discrepancy cause the failure?