Temp guage issues

[Jonkicks]

(15 Oct 2021, 10:22)Guinney1971 Wrote: whereabouts are you based?

Just wondering if there is an owner near you who could pop over with their car and try their
sender in your car to double check things.

I'm in Leicester.  I don't want to put anyone out of their way until I have tried everything I can.

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(15 Oct 2021, 15:15)Rich Hanlon Wrote: I guess if it's reading full scale deflection it must be getting the unadulterated battery voltage through it, not the reduced voltage caused by the variation in the resistance of the temp sender. So that seems to suggest to me that the green wire could be earthing directly somewhere?

My belief is that as the temp goes up the resistance of the sender goes down? So, fully hot, lowest resistance, greatest voltage at the dial, dial reads higher?

So that means that off the scale must mean no resistance at all, suggesting to me that it means the resistance between the green and black is lowest. Or shorted altogether?
The fact that it rises slowly suggests to me that the smoothing capacitor part of the guage is still working. ( I assume they have these!!)

The other source of weird gremlins is usually bad earth connection points of course. Is everything else behaving itself?

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Could check for clean connections at the engine wiring harness multi-plugs too?

What happens if you pull the wire off the temp sensor? Does it come back down or stay up?

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I've got an idea. Just humour me...

Try shutting your driver's side door?.

Almost everything else seems to be working in the binnacle - only issue is the door open light won't go off.  The gauge rises slowly as you say but did rise quickly when I shorted the sender wire to the block.  In either case it doesn't return to the bottom (be that 6 'o' clock or 100F), even with the sender wire disconnected.  I can manually flick it to the bottom (paperclip trick) but I have taken care not to do that very often.

I am going to try a few more tests later once I'm home and may tackle taking the binnacle off at the weekend to see if there is anything obviously out of place.

I have drive the car for a short distance so had the door closed for that but that was before I fitted the new sender.  All tests since have been with the door open (not sure I could lay on the floor with the door closed being over six foot but i'll try!) I will humour you and try that too.

Thanks so much for everyone's help!

Jon

[Rich Hanlon]

Ah ok.

The reason I mentioned that is that the copper leaf tabs where the multi-plugs go on to the back of the binnacle tend to be fairly thin and flappy.

I had a similar issue on a car of the same age, and I eventually traced it to two of those copper bits touching when the plug was pressed into the binnacle.

If you look at the pic Tris posted of the back of the binnacle, the tab adjacent to the temperature sender tab is the Seatbelt warning light which is either 12v or 0, not variable.

If that's touching the temp guage tab it might show full whack voltage.

I'm interested that the door light stays on too.

Just to check the above, pull the tabs off both of the drivers side door contact switches and see what happens...maybe nothing. Who knows?!

[Jonkicks]

Thanks everyone for your help.

I’ve pulled the binnacle to have a proper look at the rear.  The PO has clearly been in there trying to sort this problem already.  The PCB is not in great shape on the volt/temp side but continuity tests on the board seem to indicate it is still ok.  

In any case, I have removed the PCB (carefully) and jumped the temp guage directly from the 12v/earth/sender wire from the connector and…nothing.  No change in the gauge.  Meaning it wasn’t the PCB at fault.

I am reaching the conclusion that it is the gauge that is dead. 

After much research, the gauges in the cluster are from a 1979 Chevy but don’t look easy or even possible to transfer.

Might have to bite the bullet and go for a replacement left hand cluster.

Jon

[Rich Hanlon]

Dang. Ah well. Interested that someone has been in before. Don't throw the guage out. It might be fixable.

I've had old Renault gauges fixed here before:

http://www.speedograph-richfield.com/

They're in Nottingham. ?



My Uncle once had an MG Midget Speedo fail on him. When he had it apart on the kitchen table he found a tiny rolled up paper note inside which read "Oh no not again".