Pasha Posted July 25, 2022 Share Posted July 25, 2022 Just got my 97 car back from restoration. Had rear end TIG welded to get rid of all traces of the unsightly spare wheel carrier and had CC LED lamps fitted. All good, except the reversing lamp didn't operate.So some investigation tonight has resulted in this note. Forgive me if it's been posted before. Also excuse brevity and acronyms, in a rush here.The old bulb style RL relies on a permanent 12V and the earth is switched by the gearbox switch.The new LED one needs 12V and shares its earth with the number plate lamp.The supplied connector on the LED RL wire fits the existing loom plug fine, but the pin that expects 12V is connected to the earth. So no RL.As the other wire on the loom is 12V permanent, if you change things so the LED RL wire connects to that you get a permanently illuminated RL (ask me how I know).So what's needed is a single pole single throw (SPST) 12V relay. Connect the car loom across the coil, so the relay energises as the original bulb would have done. Siamese one side of the relay switching contacts to the permanent live you just used for the coil, and connect the LED lamp wire to the other pole of the relay switching contacts. So the coil fires when the old RL would have, and closes the contacts, therefore sending 12V to the LED lamp. Link to comment Share on other sites More sharing options...
SM25T Posted July 25, 2022 Share Posted July 25, 2022 Useful stuff. Someone was struggling with this recently Link to comment Share on other sites More sharing options...
Leadership Team SLR No.77 Posted July 26, 2022 Leadership Team Share Posted July 26, 2022 Pasha, is your solution following the same thinking as the diagram in post #25 in this thread a while ago? If it works it would be ideal to create a proper diagram to add to the site guides.Stu. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted July 26, 2022 Member Share Posted July 26, 2022 Yes, it would be very helpful to have a Technical Guide on this.That thread includes several possible solutions, including that use of a relay...Jonathan Link to comment Share on other sites More sharing options...
John Vine Posted July 26, 2022 Share Posted July 26, 2022 Re #3:Yes, it does look like it. And if so, a plug 'n' play sub-loom would be even better (#49 in the same thread)!JV Link to comment Share on other sites More sharing options...
Leadership Team SLR No.77 Posted July 26, 2022 Leadership Team Share Posted July 26, 2022 #5 Perfect Link to comment Share on other sites More sharing options...
Pasha Posted July 26, 2022 Author Share Posted July 26, 2022 Thank you everyone. That other thread is exactly what I have designed whilst looking at the back of th car, beer in hand. Have ordered the relay so it'll be sorted in the next couple of days. Luckily pre 2008 cars don't need a reversing lamp for the MOT.It's an easy fix, I just wished CC supplied something in the box. Any car with a single pole gearbox switch will have this issue.Thanks again. Link to comment Share on other sites More sharing options...
John Vine Posted July 26, 2022 Share Posted July 26, 2022 Well played, Pasha. How would you fancy the idea of documenting your design and its implementation in a Site Guide?JV Link to comment Share on other sites More sharing options...
Pasha Posted July 26, 2022 Author Share Posted July 26, 2022 I would John, the only proviso being that the other thread referred to here seems to have this already. With the exception of the solution to put a 2 pole gearbox switch in, everyone has sketched, drawn, imagined, and postulated the exact same thing. It should only take me about 30 mins with a crimp tool and some industrial velcro to get this thing up the nearside of the fuel tank and the job is done. I wouldn't have minded if there were a note in with the new lamps saying there was an incompatibility.On the plus side, the new lamps are awesome, the only issue which I thought the MoT would bring up, is the fact that if the rear lamps are supposed to have inbuilt reflectors (for the folk who don't have to use the blanking pieces and reflective strips) then they're the worst reflectors I have seen in a while. The MoT man seemed OK with them though, but in honestly even a cat with no eyes would laugh.Paul Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted July 26, 2022 Member Share Posted July 26, 2022 A *Guide would be a lot better than the two threads. Possibly something like: The problem, with photos Possible solutions, and why choose the relay solution The old circuits The new circuits Components and sources How to make the subloom, with photos How to fit the relay and subloomJonathan* And a multiauthor wiki even better! Link to comment Share on other sites More sharing options...
John Vine Posted July 26, 2022 Share Posted July 26, 2022 ...the only proviso being that the other thread referred to here seems to have this already.It does, I agree. I think the main reason TechTalk folk write Guides is to collate and publicize guidance that would otherwise be hidden away in obscure threads. Of course, writing a Guide is purely voluntary! JV Link to comment Share on other sites More sharing options...
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