Matt1969 Posted August 16, 2020 Report Share Posted August 16, 2020 Hi, A few problems with my OD control column switch. 1. Its permanently live, even when the ignition is turned off, not a major issue, but not sure this is correct. 2. The switch is not working, unless I earth the body of the switch against a part of the car (eg steering column). So I assume that the earth connection has failed and needs rewiring? Can I just bodge in a local earth? Or I should I do it properly? Thanks! Matt Quote Link to post Share on other sites
RobH Posted August 16, 2020 Report Share Posted August 16, 2020 (edited) Can you give us a bit more information about the system and the fault please Matt? Is this a A type or J type? Is the OD fitted with a 'logic circuit' or is it standard ? How do you know the switch is live with the ignition off if it isn't working? As standard the switch is not connected to earth, but if this is an A type then earthing the switch connections can bypass the gearbox interlocks and operate the relay regardless of which gear you are in. Not a good plan. Perhaps the wiring is not standard? If earthing the body of the switch pulls in the relay, it sounds as though there is something very wrong with the switch. Edited August 16, 2020 by RobH Quote Link to post Share on other sites
Matt1969 Posted August 16, 2020 Author Report Share Posted August 16, 2020 Its a Type A. The gearbox has a series of 25mm dia round switches in the top of it, but not sure if they are logic circuits? Quote Link to post Share on other sites
RobH Posted August 16, 2020 Report Share Posted August 16, 2020 (edited) No those are the transmission interlock switches. The standard circuit is below: You can see that the on/off switch has no connection to earth - it just connects between the relay coil and the interlock switches so earthing the switch body should have no effect. If doing that allows the relay to pull in, it sounds as though there is a short inside the switch. The interlock switches are 'open' until the car is in 2nd, 3rd or 4th gear, so you shouldn't be able switch the OD on until one of them is closed. Edited August 16, 2020 by RobH Quote Link to post Share on other sites
Matt1969 Posted August 16, 2020 Author Report Share Posted August 16, 2020 I think a new switch is in order.... Quote Link to post Share on other sites
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