Under dash identification

[David Goodwin]

I have taken the dash top off our Chimaera for the first time today, looking for a speedo fault. What a nest ! I wonder if one of you experts could answer two questions?

1) What is the box I have labelled A ? I have identified the rest but not this one.
2) What is there a connection to the wooden dash arrowed as B? On a metal car it would be an earth point but what is it on a wood and plastic car?

Thanks in advance.

David

[Pagey430]

For item labelled A - part no. M0559 comes up as a speedo interface unit...hope it helps :-)

[sixor8]

Is it only going to the wooden part? The lead seems to be going to the dash to act as an earth I expect (it is metal with a veneer on top, or just metal on later models), probably for the dash lights.

The box is indeed the interface unit, it ensures that the ECU gets a signal that the car is moving, so that the revs do not return to idle between gear changes. It isn't a linear signal, but just 'on' or 'off.'

[David Goodwin]

Thanks for the swift replies. Yes, since posting I have realised the back of the dash is metal (on another car of mine it is all wood, so I just assumed). Oddly it is a non factory wire and just connects to the back of the speedo, rather than to a strong earth. Still at least it makes sense now.

Great to know the other box is speedo related, especially as it is the speedo that has failed. The sensor at the back looks fine, but now so does the instrument. I might have a look in the box.

As I am in there I am trying to find a power feed when the key is on the first position, normally for the radio before the ignition comes on. Does the TVR have that? My radio needs ignition which is annoying.

Thanks again.

[Sardonicus]

Id be looking at sensor replacement first that box of tricks under the dash cover would only fail due to a solder dry joint etc IME I have never come across a faulty speedo or interface unit only the diff sensor failure on the 4 cars I have witnessed speedo drop-out or total 0 reading 2 GKN and 2 BTR

[David Goodwin]

Sardonicus - That's my conclusion as well. I am borrowing an oscilloscope to check the sensor as I am assuming it would be difficult with a multimeter.

[Loubaruch]

You dont need a scope

With a decent multimeter measure the resistance it should read a few hundred Ohms if very high the coil is open circuit.

If the coil is Ok. Next with the meter on low dc volts pass a metal object quickly across the face of the sensor you should see a very small deflection. If you do the sensor is fine

[Adrian@]

From the other day MSP6724 ...I bought one as a spare last year (which I have not fitted or tested). A@
https://www.pistonheads.com/gassing/topic.asp?h=0&...