temp gauge needle issue, what should i be looking for?

[spike blonde]

first off thanks in advance any advice/ideas.
Ill be honest its been a while since ive been on here for advice as the last few jobs on the van have been beyond my capabilities and handed over to experts, that said im hoping folks might be able to point me in the right direction on a current problem.
yesterday driving home my temp needle went from indicating temp to suddenly disappearing(as though engine switched off) even though i was still driving. was close to home so didnt panic. parked up let it cool n traced it to one of the connectors on the temp sender gauge at the engine had corroded and broke off. excellent thinks i, an easy repair. replaced the connector today starts up engine lets it warm up, the needle rises gradually up into the little white box then drops back down and doesnt come back. checked the connectors, still on firmly. tries again, same thing needle rises then falls and doesnt return.
whats the general feeling? any suggestions as to what i should look at? is it likely i need to replace the temp sender gauge? or could it be some other cooling system fault im missing?
thanks again for any advice pointers folks can give me
Spike

[MidLifeCrisis]

What happens to the needle if you take the connector off the temp sensor and ground it (to the engine block)?
The needle should go to the full hot position?

[spike blonde]

Haven't tried that, will have a go shortly. Will that tell me the electrics between dash and engine are sound?

[MidLifeCrisis]

It's a good start - it would at least prove that the needle 'can' move through its full travel in the gauge

[spike blonde]

Second to that, do I do this with engine running or just with the electrics switched on?(electricals are a blind spot for me I just don't get them)

[MidLifeCrisis]

Either - as long as the key is turned on it should work so prob easier (safer) to do with engine off, key turned in ignition

[spike blonde]

Thanks will try shortly n post back

[spike blonde]

Yeah if I ground the wires, needle goes straight to other side and red light flashes

[MidLifeCrisis]

Ok - I can't see why that doesn't prove that the gauge and wiring works ok - I'd suspect the temp sensor - is it a single wire or two wire sensor??

[spike blonde]

Two wire, blue sender. I suspect the connectors are not helping tho, recently had an unexplained supposed overheat according the gauge in the cab. Wen the a.a guy came out he did mention the cwiring connectors were aftermarket and not the correct ones not had chance to find out what the right ones are. At the moment it is two push on female connectors

[MidLifeCrisis]

Ok - if you have the two wire connection then you could also try connecting those two connector wires together - again this should make the temp gauge show full hot (and make the LED flash as you saw before)
This would confirm that the ground connection that the temp sensor uses is good;

Assuming all that works then the only other thing I can think is that the sensor is faulty

[spike blonde]

Thanks ill work on that assumption order a new sensor and take it from there, cheers for the advice mate

[spike blonde]

Ok so a little bit more info needed if anyone can explain.
Its looking like I need a new temp gauge sender for my bus, my engine is 1.9 d.g the sender fitted is 2 pin blue, but when I've gone to brickwerks page to order new the only blue one they have is not listed to be for d.g engines.do I have the wrong one fitted at the moment. The one I saw listed for the d.g was black two pin with a round sheath as opposed to the rectangular sheath on the blue one? Can anyone shed any light on this I've already had to have engine rebuilt once due to overheating probs n really cant afford to go through that again for the sake of a fairly cheap repair. Thanks for any advice,
Spike