Outside Temperature guage - Will it work? - PeachParts Mercedes-Benz Forum

tcornett · #1 11-11-2007, 11:47 PM

I have an 83 300SD and I want to have the Outside Temperature guage. My question is - If I purchase one of these units will it work in the standard intrument cluster? It appears that I have the opening to install it, but not sure of the connectivity to hook it up. I see some of these are 4 pin connectors, and some are 5 pin connectors. How would I know which one I would need without pulling the cluster?

Thank You for any insight you can provide.

Tim

Jeremy5848 · #2 11-12-2007, 12:57 AM

I don't know your car well enough to know whether it was ever offered with an outside temperature display.

In the W124 cars (I know a little more about them), the early models had a 4-pin display module and the later ones had a 5-pin version. They are interchangeable if the connector is appropriately modified. When my '87 300D arrived with a dead (4-pin) display, I was able to replace it with the later 5-pin model because the seller was able to supply me with an adapter.

If your cluster has the appropriate hole, you can use either version. You'll have to figure out the appropriate wiring and run a cable to the front bumper where the sensor lives. The best thing would be to find a car in a junkyard and take the parts that you need. Otherwise you'll need to find a schematic diagram and do some wiring.

Jeremy

Hit Man X · #3 11-12-2007, 08:03 AM

Yes, you can retrofit. Switched 12v, ground, dimmer, and to the sender by the license plate. Pretty simple to do.

ImBroke · #4 11-12-2007, 02:55 PM

Thanks Hit Man.. I want to do this to my W123. Since I'll never have PRND2 in that window, might as well have something useful. Now all I'd need are pinouts, and of course the actual parts.

Hit Man X · #5 11-12-2007, 02:57 PM

I THINK the green ran to the sender, brown is ground, black is probably the hot lead, violet is the dimmer.

babymog · #6 11-12-2007, 06:22 PM

... and in the 5pin, the extra pin is a speed input which can be left open.

tcornett · #7 11-12-2007, 09:22 PM

Thank you everyone, this is exactly what I was looking for, now off to get the parts

angst · #8 11-12-2007, 09:44 PM

Walmart has a digital thermometer near the hardware type stuff that is made to be put in your house and measure outside temp. It has a 10ft wire with the temp probe at the end and it works real nice on the dash. It has an inside/outside switch, push button to backlight, and stores high and low temps. Runs on 1 AAA that lasts ages. Ive got two of em on my dash as part of my veggie system. They look like they were meant to be there.
Super easy to install with double sided tape and best of all they are only $8.

dieseldiehard · #9 11-12-2007, 11:55 PM

Quote:

Originally Posted by babymog

... and in the 5pin, the extra pin is a speed input which can be left open.

Aha! I have been wondering what the extra pin is for!

I just installed a 5-pin LCD in place of a 4-pin one. I opened the existing plug and placed the pins in a straight 5-pin plug that came with the display module.
When I came to pin #4 I was wondering what I should do with it. I'll just leave it open.

However I get a high reading all the time, like 132F or something. I guess my sensor might not be working (heck I don't even know if its there!)

babymog · #10 11-13-2007, 06:52 PM

Sounds like you might have left the wrong pin open?

dieseldiehard · #11 12-02-2007, 12:49 AM

Quote:

Originally Posted by babymog

Sounds like you might have left the wrong pin open?

No, after much work today I discovered the problem. It was a bad sensor. I read approx. 1500 Ohms at the cable that connects to the display unit. I had a sensor cut off a cable from a donor car. It read about 4200 Ohms, and when heated briefly the value dropped quickly.
I had to remove the front bumper, then deal with the fact the MB literature for installation shows the sensor going through a hole behind the license plate.
My 124 had the sensor mounted on the L side of the inside of the bumper, near the oil cooler. I believe that is where it was located originally.

I have a theory that when located there it will get a false reading because when you come to a stop some heat coming off the oil cooler will blow around the bumper end where the sensor is (er, was).

I pulled some extra cable (there was a hank of about 3 feet of it wadded up along side the fuse box) and ran the sensor to the center of the car then through a hole in a new bumper that was waiting for project time (the old one was cracked up on one side).

Tomorrow I have to replace the impact strip but for now the sensor is sticking out of the bumper.
Voila! when I powered it up I got 54 F, about right for the cool afternoon here.
So the problem was a defective sensor!

Also, I ran a wire from the Hall Effect sensor on the speedometer to the pin 4 of the new style 5-pin Display. I believe what that does is compensate for wind chill factor, somehow it sends speed info to the display to factor that out any error due to the car moving. At least thats my theory, they use that on the later models so if it improves the accuracy then the 5-pin conversion is worth considering for anyone that has an old 4-pin display.
I know my display on the other 124 (with a 4-pin display) reads way high in the Summer, when its 90 degrees it shows over 100 or something like that. Maybe its picking up some heat from the oil cooler?
Heck this thing is just a relative indicator but I just wanted to make it work

babymog · #12 12-02-2007, 10:19 AM

Many of the '87s have the sensor located on the side, it appears to have changed somewhere in MY '87 but is poorly documented.

"Wind chill" is actually good for sensors. Although it is an approximation of how quickly bare human skin will lose heat (faster in moving air) and an estimated equivalent temperature air without wind, which has no bearing on the temperature of a sensor, the good thing is that moving air will help the sensor to read temperature more quickly (not including the heat gained from "ram effect" at near-supersonic speeds).

The purpose for the speed input on the later 5pin is to try and avoid the heat from traffic/exhaust/etc. raisiing the display temperature at low speeds. It simply slows the response time when below ~5mph.

I believe that the behind the plate frame on the front is better than the side of the bumper, but still not optimum. Behind the grille in the shade would make sense to me, if the engine is running it is always pulling air there, but the bumper works.

In all I would say that your updates are good ideas, I'll consider the hall-effect splice on my '87 next time I pull the cluster, I have a 5-pin temp sensor around somewhere.

dieseldiehard · #13 12-03-2007, 12:14 PM

Interesting, I agree that my use of "wind chill factor" was inappropriate, the sensor does work better with more air flow across it. So the input to pin 4 changes the sample rate, that seems kinda dumb now that I think about it, oh well I'll leave it there and see if it "improves" things if not I'll yank the wire off the three port terminal splitter, that big thing strapped under the seat belt buzzer which I half way replaced (man that thing is a bugger to get out!)

I note that the temp sensor cable is long enough to allow placing the sensor even on the far right side of the bumper if I wanted. It must be long to fit a S-class Lahngen version car.

If I ever get around to putting my intercooler in this car I could install a sensor at the intake manifold and one on the turbo outlet to see what the temp drop across the intercooler is. A simple switch could select between the two, now thats what a modder will think of

300Turbo · #14 12-03-2007, 09:42 PM

Mine always reads 132 degrees. 1987 Turbo.