reserve light, fuel gage connected??
 

Is the reserve light on the fuel level system in the 240d, 300d etc
independant of the gage level pointer?

When my fuel gage is at or below the last hatch mark, the reserve light doesn't come on. When I fill up I can only fill up to about 2 gals of listed capacity. So, what I am thinking is that the gage and the reserve are not connected. what says the learned members of the group??

There are separate sensors as I understand it, but in the same assembly. The warning triangle should come on when you turn the key to glow.

Sixto
95 S420
87 300SDL

Perils of an empty tank.
 

The gauge and the warning light senders are part of the same assembly and share a common ground connection. If you've never seen the warning light, it's possible that some part of its circuit is faulty.

You might consider refueling a little earlier, unless you enjoy hiking to the diesel pump and the subsequent bleeding procedure.

Phil

'84 Euro 300D, new (used) sender assembly
'85 300D

I just repaired the sending unit in my 74 240D. There was a copper ground wire inside of the sending unit that was part of the fuel warning light circuit. This wire was broken and prevented my reserve indicator from ever working. Additionally, there was a short circuit under an insulating fibre washer.

Drew

I pulled mine and cleaned it awhile back. The reserve light circuit is tied to the float. When the float reaches the bottem of it's travel, the light circuit is completed and it comes on. I checked the OHM reading on all the lines and they were in spec, gauge still off a little. I just adjusted the needle to point to exactly empty when the flat was at the bottem of it's travel. Works reasonably well, old car's fuel gauges are seldom precisly accurate. Light comes on every 450 miles or so, I put in 16 gallons, and repeat.

Wow, 450 miles on 16 gallons!

800 miles is possible if you maintain only 45mph on the highway.

The light comes on when the float inside the fuel level sender hits the bottom. It's possible that there is gunk built up on the bottom of your level sender keeping it from grounding and turning the light on.

Testing Reserve Warning Contact
 

The FSM details the procedure needed to test the warning light.

Test Warning Light