problem with low fuel warning light

[mrbizi]

I recently had the brake and fuel lines of my 94 Corolla replaced by an indy. The gas tank and fuel sending unit were also replaced with used units. Soon after I noticed that the fuel gauge warning light had stopped working (it normally would light up when there was 15 litres of gas left), and the fuel gauge was way off (gauge was showing way more gas than what the tank actually had). So I returned the car to the mechanic and he replaced the sending unit with another used one. The fuel gauge now seems to work fine, however, the low fuel warning light still won't light up (I had about 12 litres of gas left and it still wasn't lighting up).

Any ideas what could be wrong?

Thanks in advance.

[cipher93]

The first time, it sounds like he used the sender unit from a non tach car in a car with a tach (or vice versa). As for the light not coming on, it could be a fluke, but have you made sure the bulb didn't burn out? It would be an odd coincidence but is possible. I just want to know why your mechanic replaced an apparently working sender, especially with USED ones.

[mrbizi]

Originally Posted by cipher93

The first time, it sounds like he used the sender unit from a non tach car in a car with a tach (or vice versa). As for the light not coming on, it could be a fluke, but have you made sure the bulb didn't burn out? It would be an odd coincidence but is possible. I just want to know why your mechanic replaced an apparently working sender, especially with USED ones.

Thanks for your input Cipher. How do I check if the bulb is burned out (although as you said that would be quite a coincidence)? Also, do you know how this light is activated - does it have its own sensor in the tank, or is it triggered by the fuel gauge?

Good question about the sender unit, I thought about that myself. When I asked the mechanic why he replaced the original sender unit, he said the old unit and my old tank were heavily rusted and had gotten fused together that he could not reuse the sender unit, does that make sense (I have very limited knowledge in this topic)?

[speedy25]

The low fuel light turns on using (if I remember right) a thermistor. When it isnt immersed in fuel it switches to ground and the light turns on.

-SP

[cipher93]

To check if the bulb is burned out just pull out the cluster and replace the bulb with one you know that works (It's a 74, one of the small ones on the back of the cluster). I guess his reason sounds correct. I've not personally worked on the system.