Maybe you want to ask others here if they have an extra lying around. I might have one from an extra instrument cluster I have. PM me, and maybe we can work out a deal. Otherwise, have you contacted Phil???

If he is unable to help you . . . contact Pierre, the guru with all the extra OEM parts lying around at auction prices . . .. He's in Florida (Titusville)(PM me for his contact info) . . don't know his handle here, but think you'd ultimately have less problems if you just bought a new gauge for it with all the attached electronics intact.

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1983 300D, the "Avocado"
1976 240D, 4-spd the "Pumpkin", SOLD to Pierre
1984 190D, 2.2L, 5-spd, my intro to MBZ diesels, crashed into in 2002

I do have a multimeter, but not sure how do measure resistance. I know it has that horseshoe symbol, right?

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1975 300D

68R means nothing

I did some googling and I found out that R refers to no multiplier. So a 68R would be 68 ohms.

So radio shack has a 68 ohm resister but with a 5% tolerance. So it might not work, but it would be safe to try. The worst that can happen is it it will blow.

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1975 300D

Actually 5 % tolerance is better than 10% tolerance. mainly worry about resistance value and power handling or heat dissipating capacity ro wattage.

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2010 ML350 Bluetec
2012 Mustang Convertible

So with resistors, I would want to make sure that I don't use one with a lower resistance rating, right? That means more juice will get through.

If less current gets through than is normal, then my temp gauge will under read the temperature, right?

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1975 300D

if you want to put a 68 ohm resistor in there fine, that very well might be the right value. But you need a 5 watt or higher resistor. The ones that radio shack(a cell phone store) still have laying around after all these years, are likely 1/4 watt, 1/2 watt.

You will likely have to order it online. Put it in, start the car, then keep checking the gauge to see if it work right. You will also have to keep touching the resistor to see if it's getting hot. If it gets too hot it will blow in half. If it get really warm it may hold together but will likely be melting wires on your harness somewhere. It could possibly work fine for awhile and then one day you will have an electrical fire while sitting at a stop light.

With resistors you need to replace with actual value or very very close. They limit current. Capacitors have much more wiggle room, some value or larger and you are usually good to go.

Do NOT take any advice from ANYONE working at radio shack.

A 5 watt will be ceramic.

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08 R320 CDI current

Past
95 E420
87 300D Turbo 5spd
90 300TE
83 300SD
85 300TD
92 400E
85 190D

Assuming that is how the resistor works in the circuit.. sure.

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08 R320 CDI current

Past
95 E420
87 300D Turbo 5spd
90 300TE
83 300SD
85 300TD
92 400E
85 190D

Ashedd, is a 5W resistor safe?

The 68 ohms I read was off the fuel gauge resistor. It looks the same, but I don't think it is because it has no Watt rating on it, but the burnt one from the temp gauge has a "W" I can make out at the end.

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1975 300D

The temperature gauge responds to current, which depends on the voltage applied (between 12.5 and 14 volts) across the series combination of temperature sending unit resistance (variable, depending on temperature) and the resistance of the "broken" series resistor.

While the series resistor must be rated to dissipate the wattage (VČ/R or IČ*R, take your pick) at any current from cold to hot, this wattage rating will not really help you find its resistance.

So, we are back to the need to find the proper resistance value to get the proper replacement.

Now, if you know the resistance of the temp sending unit at gauge minimum and maximum temperatures (40C and 120C?) and amount of current it takes to drive the needle at these deflections, you can calculate the total resistance value and thus find your resistor value...

have you posted a wanted ad for the gauge? surely someone is parting one of these cars on this forum and has the part as a replacement - the whole gauge unit that is. for the 20 bucks or whatever it's going to cost for the used temp gauge you'd be done. it's fine to try fixing the gauge with a resistor but it's also a whole lot easier to swap in a good used unit and go on to frying bigger fish.

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punkinfair

how do you pull the cluster on the 115? I could probably check on mine after irene passes this upcoming week

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This post brought to you by Carl's Jr.

Everyone has added good info. I still believe the next step is to find another one to either buy or get the value off of.

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08 R320 CDI current

Past
95 E420
87 300D Turbo 5spd
90 300TE
83 300SD
85 300TD
92 400E
85 190D

Okay, I had the cluster out of my '81 300TD to try to fix the odometer, today, so I lifted one leg of the resistor on the temperature gauge and measured it. It is, indeed, a 68 ohm resistor. Yours is probably the same *if* the temperature sender spec didn't change between '75 and '81. I don't know the wattage spec but judging from its physical size, 5 watts should be safe.

So, you need a 68 ohm, 5 watt resistor. I checked my junk box, and I unfortunately don't have one to give you.

If there's a Fry's in your area, they'll almost certainly have it. Radio Shack might but it's a long shot; they're mostly a cell phone store now. You could also order online from Digi-Key, but you'll end up paying $15 in shipping for a $0.50 part, if you do it that way.

You will need basic soldering skills to do the replacement.

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1981 Mercedes 300TD, 1994 Honda Civic Del Sol
http://mefi.us/images/fuelly/smallsig-us/67195.pnghttp://mefi.us/images/fuelly/smallsig-us/103885.png

I think I measured an intact one on the same board and came up with 68. I strung two or three together to get 68 (Forget the values but I got them at RS.)

If you got them at radio shack, then they weren't 5w, but like a 1/4 watt. I checked them out and they had the right resistance but the wattage was wrong. Maybe that is why you have had no success.

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1975 300D

AHa, the saga is not finished yet it seems.

The temp gauge works fine. Except if I put the light switch on. Then is pegs out max.

Now I am totally at a loss.

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1975 300D