Efuentes Posted June 21, 2021 Report Share Posted June 21, 2021 Hello everyone. Greetings from Spain. My OD decided to stop engaging. Clearly an electric problem, as I didn’t hear the solenoid clicking. I have tracked down the issue to the gearbox switches or the gearbox ground wiring, as there is no current coming from the yellow cable that goes from the gearbox to the OD switch in the steering column. I removed the yellow cable coming from the gearbox from the connector that joins it with the yellow cable going to the switch and substituted it with a cable to ground (ie: by passed the gearbox switches), and the OD engages when I activate the switch. That implies that the relay is good, the solenoid is good, the column switch is good and the wiring that goes to the relay from the switch (green / yellow), from the ignition switch (white), from the Control Box (Brown) and to the OD solenoid (yellow / purple) is also good. The yellow cable that links the gearbox switches which, in turn, are connected to earth, with the OD switch in the column, seems fine, so the issue seems to be in the gearbox switches or their ground connection. By the way, thanks to everyone in the TR register forums, as all the above was knowledge I obtained from it, myself being a complete ignorant on the matter before consulting the forum…. If the issue are the gearbox switches, that would require a gearbox cover removal and a prayer that the issue is just the outside connections rather than those inside the selector box. Before going that route, however, I had the hope that maybe the issue is the wire that connects the gearbox switches to ground (which I checked in other posts in the forum and learnt is via a wire, not with the gearbox case), and also hoped that such connection may be visible from below, not requiring to remove the gearbox cover. Does anyone know and, if possible, have a picture of how and where the gearbox wiring connects to ground?. Many thanks in advance Quote Link to post Share on other sites
RobH Posted June 21, 2021 Report Share Posted June 21, 2021 Second half of this video shows the actual wiring. I don't think you will get at it without taking the transmission cover off. Quote Link to post Share on other sites
Efuentes Posted June 21, 2021 Author Report Share Posted June 21, 2021 3 hours ago, RobH said: Second half of this video shows the actual wiring. I don't think you will get at it without taking the transmission cover off. That’s very useful, thank you. It looks like the black wire goes from the switch to the front, presumably to an earth connection in the body of the car, above the bellhousing. I agree it looks like a transmission cover off work… I will peep from underneath and from the engine compartment to see if I have any luck… Quote Link to post Share on other sites
Efuentes Posted June 22, 2021 Author Report Share Posted June 22, 2021 Given that currently, and not for long, is TR4 time in Spain (that is, weather not too hot to drive the TR4), that I have an excursion planned for this weekend and that I have no time before the excursion to tackle the gearbox switches issue, I was thinking of temporarily bypassing the Gearbox switches so I can use the car this weekend. I normally only use OD in 4th gear and will put a sticker in the dashboard to remind me to disconnect it before I engage reverse or 1st gear. I do have an OD on indicator light, which is key. Should I forget to disengage OD when on the road, is there any risk if I bypass the switches and I reduce to 3rd gear from 4th?. I have done that some times in the past, but, while the light stayed on, I am not sure if the OD disengages temporarily automatically when changing gears (ie: disengage when I move the gear lever, and engage again when the new gear is selected), which would not happen if I bypass the switches or if it remains on. If it does disengage, is there damage risk if I change gears with the OD on?. Quote Link to post Share on other sites
Hamish Posted June 22, 2021 Report Share Posted June 22, 2021 to be honest i would just disable the OD and not risk the muscle memory of using it and risking the reversing catastrophe Quote Link to post Share on other sites
tthomson Posted June 27, 2021 Report Share Posted June 27, 2021 Efuentes, The gearbox switches are connected in parallel and the ground wire connects from one switch to the other and then normally connects to one of the bolts holding the gearbox cover in place. If the problem occurs for both switches, then it it is probably a problem in a connection in the ground. These are normally crimped connections, and any crimped connection subject to oil, water ingress and dirt, can become resistive, which will exhibit the fault you are experiencing. If this is the case, don't be tempted to solder the connection, that just adds an electrolytic corrosion option into the mix. Crimping is still the better option for this. Quote Link to post Share on other sites
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