[modern] '88 XJ40 Sovereign A/C Controls

In the Haynes Manual on Page 3.11 at item 12.9 it is stated:

‘On 1988 and 1989 models, if the climate controls do not respond to any
driver input, check with your Jaguar dealer before renewing the ECU or
control panel. A service part is available (a resistor, #JLM 1901) that can
be installed at one of the control panel terminals that may fix the problem
without any other parts being renewed. Instructions are included with the

Does anyone know what this resistor does? I have got hold of one but
instructions were NOT included with it! Does anyone know where and how it
should be fitted? Has anyone tried this and did it do any good?


Paul. '88 XJ40 Sovereign. London NW7.