Pagoda SL Group

W113 Pagoda SL Group => Electrical and Instruments => Topic started by: GMAN on July 27, 2025, 11:46:10

Title: Red Low Level Fuel Light
Post by: GMAN on July 27, 2025, 11:46:10

Hi,
The red low level fuel light is on permanently but the fuel indicator seems to work OK. Can anyone suggest the possible cause and remody.

Thanks
Graham

Title: Re: Red Low Level Fuel Light
Post by: rwmastel on July 27, 2025, 12:40:58

May I recommend you create a signature so your cars' model year is on each post you make?  Earlier 230SLs had a different in-tank fuel sender unit and maybe that makes a difference here?

Title: Re: Red Low Level Fuel Light
Post by: BobH on July 27, 2025, 12:49:37

Hello Graham, the lamp is fed from contacts in the fuel sender, so it could be a bad sender, if you pull the plug from the sender in the boot, see if the light goes out.  If not report back and we can suggest other tests to try

Title: Re: Red Low Level Fuel Light
Post by: GMAN on July 27, 2025, 15:20:39

Hi Bob,
Unplugged it. Red light went out. I cleaned of the pins and re-tried the plug but the light comes on. The fuel guage reads more than 1/2 so its not that.

Title: Re: Red Low Level Fuel Light
Post by: GMAN on July 27, 2025, 15:22:44

The car is a 1966 230sl auto.

Title: Re: Red Low Level Fuel Light
Post by: BobH on July 27, 2025, 15:45:28

Sounds like the contact in the bottom of the sender is either shorting out due to a build up of crud, or the wires are shorting out.  The internal contact should be open circuit until the float drops when the fuel level is almost empty.  It's a different circuit to the gauge, so that's why the gauge is still working.  They can be taken apart carefully, might be worth a look inside.  I assume it's the cylindrical type rather than the one with the external float.  Best disconnect the battery before pulling it out

https://www.sl113.org/wiki/Fuel/SenderUnit

Title: Re: Red Low Level Fuel Light
Post by: Pawel66 on July 27, 2025, 17:12:26

If it goes off when you unplug and back on when you put the plug back on - I am pretty sure it is the switch in the sender. It disconnects the ground. If there is ground on the pin that goes to the plug, the light will be on.

Removing the sender is not that difficult. You need to be careful as you work with fuel, undo the nuts carefully not to break off the studs and have a new gasket at hand.

Title: Re: Red Low Level Fuel Light
Post by: GMAN on July 28, 2025, 08:13:41

Thank you gentlemen.
Ive ordered the gasket and started blasting the nuts with release agent - they are a little crusty. I'll update you later this week once the gasket turns up.

Title: Re: Red Low Level Fuel Light
Post by: rwmastel on July 28, 2025, 13:35:42

GMAN,

Nice signature line.   ;D  Also, welcome to the Group!  I see you recently joined.  We have a lot of active members in the UK, I'm sure you'll have opportunities to meet up in person and get to know people.

Title: Re: Red Low Level Fuel Light
Post by: GMAN on August 03, 2025, 12:52:03

Too much corrossion on the old sender to had to replace it.
All good now

Title: Re: Red Low Level Fuel Light
Post by: Pawel66 on August 03, 2025, 16:42:01

You replaced the sender and it all works?

Title: Re: Red Low Level Fuel Light
Post by: GMAN on August 05, 2025, 11:27:00

Yeh,
100% all good. Next the Kick-down switch !!!

Title: Re: Red Low Level Fuel Light
Post by: Pawel66 on August 05, 2025, 11:33:10

Lovely, thank you. I was worried you got into trouble with sender/gauge compatibility.