TractorMechanic Posted April 30, 2021 Report Share Posted April 30, 2021 I'm sure that this subject has been covered before but I can't find any reference to it. I want to add a reversing light switch to my 4a gearbox and wanted to know who else had done and how it was achieved. Thanks Quote Link to post Share on other sites
RobH Posted April 30, 2021 Report Share Posted April 30, 2021 Welcome to the forum TM. I believe the answer is going to depend on whether your car still has its original gearbox and what the top cover looks like as there were several variations. The later boxes had provision for fitting a reversing switch in one of two positions. This link is about overdrive inhibit switches but there is some info about the reversing switch too: https://static1.squarespace.com/static/5c6dec53b10f25d4edf0b3f7/t/5d0195838ed02e0001596bc0/1560384900296/OD+Isolator+Switches.pdf Quote Link to post Share on other sites
TractorMechanic Posted April 30, 2021 Author Report Share Posted April 30, 2021 RobH, Many thanks this is a great start. Looking back at a picture of my gearbox I can see that there is a third position to put the switch. I only wish I had thought about it when it was out of the car! Thanks again. Quote Link to post Share on other sites
jpmf Posted April 30, 2021 Report Share Posted April 30, 2021 AFAIK, and can remember, the reverse switch is opposite the blanking plug in the top cover where the OD joins the GB in your picture above. As I have the top cover off I can have a better look tomorrow, unless I'm beaten to it.... Quote Link to post Share on other sites
RogerH Posted April 30, 2021 Report Share Posted April 30, 2021 This where I fitted my rev light switch Make sure that the selector 'fork' has the correct profile to actuate the switch Roger Quote Link to post Share on other sites
TractorMechanic Posted April 30, 2021 Author Report Share Posted April 30, 2021 (edited) Hi Roger, thanks for confirming with your photo what is the correct profile on the selector fork I am looking for? what is the thread size I need to cut into the gearbox cover to accommodate the new switch? jpmf, If you could post the picture of your gearbox cover that would be helpful to. Thanks Rupert Edited April 30, 2021 by TractorMechanic Quote Link to post Share on other sites
peter clarke Posted April 30, 2021 Report Share Posted April 30, 2021 correct thread is 16mm course Quote Link to post Share on other sites
RogerH Posted May 1, 2021 Report Share Posted May 1, 2021 9 hours ago, TractorMechanic said: Hi Roger, thanks for confirming with your photo what is the correct profile on the selector fork I am looking for? what is the thread size I need to cut into the gearbox cover to accommodate the new switch? jpmf, If you could post the picture of your gearbox cover that would be helpful to. Thanks Rupert Hi Rupert, I can't find a pic with the fork profile but it would be obvious when you get access to it. As Peter states the tap used is 16mm x 2mm (12.7tpi) - this works well but not the actual size. It should be 5/8"UNF x 13tpi. However this is a special size not readilyt available. At least one restorer has the correct size. Why did they use a thread size that is odd!!! Roger Quote Link to post Share on other sites
Z320 Posted May 1, 2021 Report Share Posted May 1, 2021 See here all about Quote Link to post Share on other sites
qkingston Posted May 1, 2021 Report Share Posted May 1, 2021 Hi Rupert, I have just done this. 12mm drill and M16 tap. When you drill the hole go carefully, the reverse selector rod is just underneath; I slid some thick gasket paper over the selector rods to capture any swarf and provide a little protection. The M16 tap works fine with the thread of the isolator switches. The reverse selector rod has a small indent cut into it so that in fwd gears the ball bearing of the switch sits in this cut-out, when reverse is selected the full profile of the rod depresses the ball bearing and makes the switch. Easy to check that works ok when installed, with an resistance meter Hope it goes ok David Quote Link to post Share on other sites
TractorMechanic Posted May 1, 2021 Author Report Share Posted May 1, 2021 Peter, Roger, David and Z320 Many thanks for your help and time! Quote Link to post Share on other sites
tthomson Posted May 1, 2021 Report Share Posted May 1, 2021 After fitting the switch, wiring it in will need some thought. If it is to go to Earth, then the reversing lights will need a live feed and an insulated return to the switch. I chose a different option, I assumed that the switch would be earthed, but so too would one side of the reversing lamps (fewer wires running from rear), so I added a relay controlled by the switch that supplied the live feed to the lamps. TT Quote Link to post Share on other sites
Z320 Posted May 1, 2021 Report Share Posted May 1, 2021 Hi Tractor, on Roger's photo you see all switches have spades (bended) sideward, if you buy a new one they are probably indicating up, so bend them carefully down before you @€&?!()@ with the gearbox cover. You can call me Marco, Ciao Quote Link to post Share on other sites
stuart Posted May 4, 2021 Report Share Posted May 4, 2021 I do have the correct drill and tap FWIW. Stuart. Quote Link to post Share on other sites
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