Ed White Posted May 29, 2023 Share Posted May 29, 2023 Changed the scruffy rear wings on my old ex racer. Unplugged lights, plugged back in, all good but no brake lights. It passed mot last weds so I'm assuming they worked then. I've put a multimeter on one side of the pedal switch and it only shows a fraction of one volt? With the pedal down and the switch open it reads the same voltage at the other side. So it's like the switch isn't getting a 12 voltage feed, but is getting a very small feed. Help please, I'm lost now? Cheers Ed Link to comment Share on other sites More sharing options...
Area Representative Paul Richards Posted May 29, 2023 Area Representative Share Posted May 29, 2023 Faulty switch is a very common problem. Remove both wires from switch and with ignition on touch them together. If lights work switch is broken. Replace with a better quality one from Car Builder Solutions. Link to comment Share on other sites More sharing options...
Ed White Posted May 29, 2023 Author Share Posted May 29, 2023 Thanks Paul, I'll try it, but the lack of voltage at the switch makes me wonder if it that? Link to comment Share on other sites More sharing options...
Ed White Posted May 29, 2023 Author Share Posted May 29, 2023 It's not getting power to the switch, so maybe just a fuse. Bypassing the switch directly brings the ights on. Link to comment Share on other sites More sharing options...
Jonathan Kay Posted May 29, 2023 Share Posted May 29, 2023 "It's not getting power to the switch, so maybe just a fuse. Bypassing the switch directly brings the ights on."That's with a test jump wire to the lamp unit?Jonathan Link to comment Share on other sites More sharing options...
Jonathan Kay Posted May 29, 2023 Share Posted May 29, 2023 1 Incandescant lamps or LEDs?2 Do you have the wiring diagram and fuse layout, and if not would you like a copy?3 Did you remove the fuse before doing the work? Check that it's there, seated and not blown4 As above: Ignition ON then connect the two wires at the switch... do the lights come on?5 Ignition ON: what's the voltage between the input side of the switch and a good earth? With the same setting what's the reading across the battery?6 Ignition OFF: set the meter to some resistance range and measure the resistance across the switch with the plunger relaxed and then pressed.7 While you're there watch the action of the pedal on the switch: does it look adequate? And does the switch feel smooth when you close it by hand?Jonathan Link to comment Share on other sites More sharing options...
Area Representative Paul Richards Posted May 29, 2023 Area Representative Share Posted May 29, 2023 "Bypassing the switch directly brings the lights on."Dies this mean you are running a feed direct from the battery to somewhere? Not sure I understand. Link to comment Share on other sites More sharing options...
7 wonders of the world Posted May 29, 2023 Share Posted May 29, 2023 Linky for the CBS switch: https://www.ebay.co.uk/itm/281855443589?hash=item419fe4c285:g:LvMAAOSwd4tT0N2u Link to comment Share on other sites More sharing options...
SM25T Posted May 29, 2023 Share Posted May 29, 2023 You do have ignition on ? Link to comment Share on other sites More sharing options...
Ed White Posted May 31, 2023 Author Share Posted May 31, 2023 Turned out to be a fuse, thanks folks, but didn't come across as a fuse as during my first test with the multimeter it recorded a small amount of voltage? Never mind, all sorted. I learned a bit from reading previous posts. I now know how to check resistance. Every day is a school day Link to comment Share on other sites More sharing options...
Jonathan Kay Posted May 31, 2023 Share Posted May 31, 2023 Well done. And thanks for adding the answer.That small voltage might have been the result of something connecting through an unusual route at very low current.Jonathan Link to comment Share on other sites More sharing options...
ChrisC Posted May 31, 2023 Share Posted May 31, 2023 The low voltage on the brake light switch could be a sign of a bad earth, and the circuit is earthing back through the brake lights (and the other bulbs). It may be worth removing the fuse again popping the meter on the switch and seeing if you can remove that small voltage with a cleanup of the rear light earth connections. Link to comment Share on other sites More sharing options...
LouisFeakes Posted June 7, 2023 Share Posted June 7, 2023 Just had exactly the same issue.Fuse replaced and all working fine...but only after ordering a new switch!!! Link to comment Share on other sites More sharing options...
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