Fuel guage red light stopped working

[revilla]

Hello readers,

Last week my low-fuel red light stopped working.  Don't ask me how I found out  .  Luckily I carry a small reserve container.  Fuel gauge still works fine the complete range full-empty.

Checked bulb.  Tested fine.
Checked black receptacle/nest contacts.  Fine.
Check contacts on sender unit.  Nice and clean.
Didn't want to disassemble sender unit yet.  Thought it was better to ask you for recommendations first as I never done that before.

For those of you who had same issue before, or those who know how the system works electrically, what do you recommend I check next?

I'm familiar with taking the cluster apart as I recently cleaned the plastics, needles and dials from inside.  Not excited about doing it again, but will do if needed.

Thanks in advance for the help.

[UTn_boy]

The problem will likely be in the sending unit. Since the bulb tests good and the plug connections on both the cluster and sending unit are clean, there isn't much left to be wrong.  Granted, the printed circuit in the cluster housing could possibly have split or gone open, but that is highly unlikely.  Take your sending unit out and clean the dirt out of it. 

[revilla]

Thanks Aaron.  Will do.

I'll check too continuity of the wires between sending unit connector and cluster in case something broke in between.

So, it means that the red light comes on responding to a signal from the sending unit?  Or, does it come on following a contact closing right at the cluster/PCB of fuel gauge itself?  Maybe mechanically at gauge once the needle reaches low?

Thanks

[Harv]

Our cars have a fuel light?

[daantjie]

Mine does. I see it often driving a 6.9 

[gavin116]

Here's a picture, albeit from a R107, but same thing really.  My light is erratic and the needle is bouncy.  I'm changing the fuel sender unit under the first-aid box sometime in the very near future to see if I can get things working like they're supposed to.  Hope the picture helps.

[Harv]

I honestly had no idea that triangle lit up. I thought it was just there to point to which side the fuel filler cap was on.

[Jed]

LMAO
but the fuel filler cap is on the other side of the car !!??  (at least on the 6.9 it is)

[Harv]

LMAO
but the fuel filler cap is on the other side of the car !!??  (at least on the 6.9 it is)

The 'arrow' points to the passenger side of the car. So it's correct.

[UTn_boy]

Revilla, yes, the warning light comes on as a result of the float in the sending unit bottoming out.  There is a brass ring on the bottom of the float in the sending unit.  When it bottoms out, it's essentially closing the circuit for the warning light.  Or, in other words, the "light switch" is flipped to the on position.  Of course, when the tank is refilled, the float rises with the fuel level, at which point the fuel warning light circuit opens because the brass ring on the bottom of the float is no longer in contact with the two connection at the bottom of the sending unit.  What usually happens is the bottom of the sending unit builds up with silt and dirt.  This disallows the fuel warning light circuit from working.  Sometimes the chrome/nickel plated shaft that the float rides on will rust and cause the float to stick, which can also lead to the fuel gauge dancing around.  Just be careful when you take it apart.  There are two human hair sized wires that the float slides on.  They break really easily. 

[revilla]

Thx for the tech explanation and advice.  I now need to find me the right tool to undo that huge hex-shaped piece that holds the sender in place.

[Diesel 617]

Here's a picture, albeit from a R107, but same thing really.  My light is erratic and the needle is bouncy.  I'm changing the fuel sender unit under the first-aid box sometime in the very near future to see if I can get things working like they're supposed to.  Hope the picture helps.

THANK YOU! What an 'ohhh' moment

The R means two things Refill and Reserve. What incredible amount of thought put into that gauge! Wow! Much better than American thinking of having an E for empty

Thank you for posting the picture showing how the measurements work.

[ptashek]

Thx for the tech explanation and advice.  I now need to find me the right tool to undo that huge hex-shaped piece that holds the sender in place.

A pipe wrench does wonders here

[Diesel 617]

Thx for the tech explanation and advice.  I now need to find me the right tool to undo that huge hex-shaped piece that holds the sender in place.

A pipe wrench does wonders here

46mm Socket also will work, in case you happen to have one laying around

[Type17]

My light has never worked (in fact, I only noticed it a long time after I got the car, when the sun was shining directly on the face of the gauge).


Question for those with a working light: Does it light up as a self-test when the ignition switch is on, before the engine is started? - If so, I might just have a blown bulb, if not, it could be the bulb, or a problem in the sender unit.