Geo55

My assumption is that the low level fuel circuit is open while the fuel level is above reserve but once it goes to reserve level the circuit closes and sends a signal to the brain to turn on the warning light. When my yellow is connected it always triggers the low fuel level warning. I can turn it off with the warning button. That wire was never connected and was wrapped with electrical tape. Trying to find out if there is a fix. Thanks Forgot to mention that I tested the circuit while it was out and it was closed no matter where the float was. (Yellow post to Ground post)

dr bob

For your 1987 (pre-digidash S4) there are three conductors from the fuel level sender itself. The solid brown conductor goes to MPVI in the spare-wheel well. Violet-with-Black is the "wiper" that changes resistance to ground based on the position of the float. Green-with-Black is the contact for the low-fuel light, connecting to the Violet-with-Black when fuel level drops to a low level. The actual float position when that contact is made is not shown on the electrical drawing. Violet-with-Black passes through pin 2 of a 14-pin connector in the rear and on to the gauge cluster. Green-with-Black connects through pin 1 of that same 14-pin connector, then on to pin 13 in the yellow connector for the Central Information controller for the display.

WSM page 90-38 includes some testing details if you want to demo/verify correct function of the low fuel warning through the Central Information display. With key on and a jumper between terminals W & T, the low fuel warning should come on after about ten seconds. the caption by the picture there says:

Switch Function:
Reserve fuel level = contact made
Greater fuel level = contact open

There is no description of the actual level beyond the narrative/subjective "Reserve Fuel Level".

The low fuel warning come on in my '89 (same sender...) with about 3 gals left in the tank.

Geo55

Thank you Dr.Bob. Great clarification. I went through the WSM fuel section but did not find much on the low level fuel light. I am removing the Sending unit again for another cleaning but first will test the unit per your information and look through the WSM for that section. Thanks again for the reply. I will post any findings.

Geo55

So I pulled the sending unit again and soldered the copper wire back to the broken section. Then I took a good look at the unit since I never got a signal from the low level post. Taking a good look I noticed that maybe something else may be broken. Does anyone know if the recessed section on the left needs to be bridged to the contact point? My guess is that it does but I want to draw on the expertise of my fellow 928 owners instead of screwing something up. Thanks in advance

Geo55

So I bridged the section on the left where it was missing the broken piece (Pictured above on the left side) and it is now functional again.

Mrmerlin

nice you just saved yourself about 400.00 for a new sender