Interchanging W123 fuel sending units--Can it be done?
 

Well the 240D fuel sending unit works but the reserve light switch in the sender does not work. I have had it apart and cannot get it to work. The ground plug for the reserve light seems to have a bad connection. The level unit does work. Produces good resistane and moves the guage.
I may attempt to solder the ground connection to see if I can fix it. Who knows!!!!!!!!!:(

Here's the question
The fuel sending unit for my 240D is (VIN number 363866) is $271.00. But VIN number -306958 and 396577- are only $114.

Whats so different about the sender in my car. Nothing is in the Service Manual about the differance. I would assume the size is the same because the tanks are the same. Maybe the resistence is different. Or the actual guage is designed for a different resistance.

Does anybody know???

Dave
7709

I have no idea about the answer to your question. But is it really necessary to have the reserve light? I always fill up with the "first available Diesel" once the gauge reaches 1/4.

Well go figure
I cleaned and recleaned the sending unit trying to get the reserve light to work and it just would not test correctly. I decided to go with Rick Mileys advise and just have her refuel when the guage got to 1/4 full, which is not a bad idea anyway, keep all the crud away form the screen. My daughter and son went to a friends house last night and took the 240D. Just a few minutes ago my son asked how much fuel the car has when the reserve light comes on. I told him its broken and won't come on. He told me it came on last night. So the Texas A&M Gods fixed the sending unit ( For those who don't know. The car was bought new by an Aggie, his son drove it at A&M and then his brother drove it at A&M) . That's OK with me. Now if I could just get the reserve test to come on.
However I realized while talking to my son about the light. the ground for the test goes to the Alternator and the warning circuit for brakes. The brake wear light is on and will not extinguish. I'm now thinking that the warning circuit may have something to do with the reserve light and brake wear warning light.

Dave

I swapped out the Warning circuit, which all the online sites call the "seat belt warning relay" with the one in the 82 300TD. The units are the same, and the brake wear warning light now goes out after the car is started. So some success. However the fuel reserve light still does not test. I will get a new Seat belt warning relay and try it again, I have a feeling that the new relay will fix all the problems.
I'll let you know when get the new relay

Dave :)
7709