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Low fuel light SE5a - how does it work?

Posted: Tue Apr 09, 2019 11:02 am
by larrylamb11
Does anyone know how the low fuel light works on the SE5a? It must be pretty simple as it's old technology.
I am having an issue with mine where the low fuel light is illuminating when there is still masses of fuel in the tank. The gauge is working properly, reads full when full and close to empty when the tank is empty. I'm pretty sure the sender is working properly too - I recently had it out and tested resistance through the range which seemed to reflect the sort of OHMS numbers it was supposed to return (I think I'd found the numbers on here somewhere).
I see the fuel light is controlled by a little 'can' under the dash with four connections, inside which seems to be a sort of points contact and a what looks like a bi-metallic strip? It looks pretty simple..... Is it adjustable for sensitivity?

Low fuel light SE5a - how does it work?

Posted: Tue Apr 09, 2019 11:19 am
by Corky
Sounds like you’re talking about the voltage regulator. It’s there to maintain a 10v supply to the fuel and temperature gauges. The bimetallic strip rattles around switching off the 12v to keep an average of 10v.

On all my big Scimitars, I swapped them out for an electronic version. You can pick them up on eBay for around £12. They’re the same item on MGs and Triumphs of the same era.

Low fuel light SE5a - how does it work?

Posted: Tue Apr 09, 2019 11:23 am
by AJL Electronics
larrylamb11 wrote:
Tue Apr 09, 2019 11:02 am

I see the fuel light is controlled by a little 'can' under the dash with four connections, inside which seems to be a sort of points contact and a what looks like a bi-metallic strip? It looks pretty simple..... Is it adjustable for sensitivity?
Yes that is the fuel warning light controller. Not sure if it is adjustable. Whip it out and have a good look, you can peel back the tabs to get inside. Not sure how you would get a new one, but simple enough to build with something like an LM393 comparator.

Low fuel light SE5a - how does it work?

Posted: Tue Apr 09, 2019 11:25 am
by scimjim

Low fuel light SE5a - how does it work?

Posted: Tue Apr 09, 2019 11:27 am
by Corky
Ahh yes, I’d forgotten about the other device. It’s been a while since I was under the dash of a 5A.

Low fuel light SE5a - how does it work?

Posted: Tue Apr 09, 2019 3:53 pm
by larrylamb11
Aha, excellent, thank you! I understand how it works now.... Now I can mount and orient it correctly and see how much adjustment it needs....

Low fuel light SE5a - how does it work?

Posted: Tue Apr 09, 2019 4:40 pm
by peter freeman
Note that if you buy a new sender it will more than likely come with a low level connection which you can wire up to the low level light and thus then by-pass the interface - you will of course have to run a wire from the sender to the lamp.