Dishwasher rinse aid oddity

Having a few spare moments today, I decided to have a nose at our (Hoptpoint SDD910) dishwasher rinse aid light.
INitially it was stuck on. a few months ago (I posted then to general "don't bother with rinse aid" advice :) )
Then it went the other way, and hasn't come on for months.
When you power on the machine, it flashes all lights, so it's not a question of the light/bulb having failed.
Dismantled front of machine - very easy. Removed rinse-aid/tablet holder assembly.
Inspected, and found an open circuit in the 2-wire cable between the rinse aid dispenser and the main board.
Replaced wires - tested from both ends - all OK.
Reassemble and (have you guessed ?!) - the rinse aid warning still doesn't work ....
Given the control module has (as I explained to SWMBO) "electronics up the wazoo" - is it likely there is some logic with some other components which is (also) failing ?
Just shorting the two wires by hand doesn't trigger the light. Door open. Door closed (in case there's an "ignore if door open" logic).
I think we'll get by, but it is intriguing ....
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Bet you didn’t manage to replace the cable properly.
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On Fri, 23 Sep 2016 15:40:12 +0000, Jethro_uk wrote:

Following on from this, yesterday, the light came on ! Since I knew there was no rinse aid, I filled it up and - it went off !!!!
I wonder if the synchronistic post from Tim hints at the reason being due to a "gunged" tank which has now - as a result of my intervention - ungunged ?
If this is the case, it suggests the previous *in*operation of the light was in fact correct, and the rinse aid wasn't being dispensed !
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