Napoleon Posted April 25 Report Share Posted April 25 Please could someone advise me on how to fit this kill switch? It has two connectors for large cables and on the base two connections marked '1' and another two marked '2'. I want to fit it in my 1958 TR3A, now negative earth with an alternator and dummy regulator box. I will be putting it in the cockpit within easy reach in case of an emergency (there's nothing like the smell of burning plastic in the morning . . . ) I'd like it to completely shut down all the electrics. Many Thanks Rod Quote Link to post Share on other sites
Charlie D Posted April 25 Report Share Posted April 25 Rod, If you want it to cut everything off then fit it in the earth lead from the battery. One of the big connectors goes to the battery, the other to the car body (Where the other end of the earth lead had been.) Does that lever come off? (Some do). If so I'd glue it on permanently or pin it. The last thing you want before the apocalypse is to find your knob has dropped off. I'd just ignore the two smaller connectors. Charlie Quote Link to post Share on other sites
RobH Posted April 25 Report Share Posted April 25 (edited) The switch has two separate functions. The heavy connections are to isolate the battery from the electrical system, but that won't stop the engine if it is running since the alternator will continue to supply power to the car, and if that is the case it will also be powering any electrical short that might have occurred. The smaller contacts are intended to be wired into the ignition system so that switching off also removes power from that circuit so stopping the engine and any output from the alternator. The contacts labelled '1' are closed with the switch off and open with it on. The contacts labelled '2' are open with the switch off and closed with it on. Most of the manufacturer's fitting instructions show the main switch wired in the live lead from the battery to the solenoid. That scheme is not entirely safe because if some metal item comes in to contact with the battery live terminal or wiring before the switch, and also touches the bodywork (or if in the event of a crash some deranged bodywork touches that terminal), there will be a short circuit. The better scheme is as Charlie says, to put the switch in the battery earth connection. That is safer because when the switch is off the battery is then 'floating' so that earthing either terminal to the body cannot cause a short circuit. Auxilliary switch '2' can be wired in series with the supply to the ignition coil so that power is cut with the switch off. The easiest point to do that is probably in the power wire to the coil itself. Contacts '1' can be used to earth out the supply via a high-power resistor but that isn't really necessary except for alternators having a battery-sense connection, where removing the connection suddenly can damage the alternator from a voltage spike. Lucas ACR alternators do not need this. Edited April 25 by RobH Quote Link to post Share on other sites
Lebro Posted April 25 Report Share Posted April 25 (edited) Click on to enlarge I have the same switch, I switched the live battery terminal, as shown. The small terminals interrupt the volts going to the coil, to ensure the engine stops when switched off even if ignition switch is still on. The switch lever is positioned below the glove box for easy access. Bob Edited April 25 by Lebro Quote Link to post Share on other sites
iain Posted April 26 Report Share Posted April 26 Revington do a kit designed to fit under the dash https://www.revingtontr.com/product/rtr8319k/name/kit-cut-out-under-dash-tr2-4a I guess you could copy the bracket design. Iain Quote Link to post Share on other sites
Charlie D Posted April 26 Report Share Posted April 26 Bob, I notice that you have a small wire that goes off somewhere that is connected directly to the battery earth even when the switch is switched to “off” . I would guess tracker or something similar, but what other devices may need to always be alive? Charlie. Quote Link to post Share on other sites
Ralph Whitaker Posted April 26 Report Share Posted April 26 54 minutes ago, Charlie D said: Bob, I notice that you have a small wire that goes off somewhere that is connected directly to the battery earth even when the switch is switched to “off” . I would guess tracker or something similar, but what other devices may need to always be alive? Charlie. Clock?, or memory to a radio. Ralph Quote Link to post Share on other sites
RobH Posted April 26 Report Share Posted April 26 (edited) 59 minutes ago, Ralph Whitaker said: Clock?, or memory to a radio. Decadence ! This is a sidescreen car . A period radio would be manually-tuned and any clock would be wind-up. Seriously, if you leave something like that connected you haven't really isolated all the electrics, so it depends on what you are trying to achieve. If there is a radio which needs continuous power you can't put the battery switch in the earth lead because the radio probably earths through its mounting bracket. Edited April 26 by RobH Quote Link to post Share on other sites
Ralph Whitaker Posted April 26 Report Share Posted April 26 16 minutes ago, RobH said: Decadence ! This is a sidescreen car . A period radio would be manually-tuned and any clock would be wind-up. Seriously, if you leave something like that connected you haven't really isolated all the electrics, so it depends on what you are trying to achieve. If there is a radio which needs continuous power you can't put the battery switch in the earth lead because the radio probably earths through its mounting bracket. Only suggesting !, I don`t know what Bob has wired up. I do have a clock in my 3a , though no radio. Ralph Quote Link to post Share on other sites
Charlie D Posted April 26 Report Share Posted April 26 30 minutes ago, RobH said: ...If there is a radio which needs continuous power you can't put the battery switch in the earth lead because the radio probably earths through its mounting bracket... Maybe that's why Bob put his switch on the live side of the battery. 31 minutes ago, RobH said: ...any clock would be wind-up... So... Tell us about the last time you saw a wind up clock in a TR Quote Link to post Share on other sites
RobH Posted April 26 Report Share Posted April 26 5 minutes ago, Charlie D said: So... Tell us about the last time you saw a wind up clock in a TR Well not in a TR Charlie, but back in the '70s I had one in my AH Sprite. Couldn't afford a 'leccy one. Quote Link to post Share on other sites
Lebro Posted April 26 Report Share Posted April 26 17 minutes ago, Charlie D said: ...If there is a radio which needs continuous power you can't put the battery switch in the earth lead because the radio probably earths through its mounting bracket... Maybe that's why Bob put his switch on the live side of the battery. Nearly. It was to keep my tracker alive in the event of me leaving the car somewhere with red key out. If you look carefully at the close up photo of my switch (above) you will notice a thin red wire on the left hand big (live) terminal. Bob Quote Link to post Share on other sites
Napoleon Posted April 26 Author Report Share Posted April 26 Thank you everybody for this very helpful information :-) I can now start fitting it for extra peace of mind/safety - A long time ago (late 1970s), I had an under bonnet electrical fire in a fairly new Stag and ever since I have carried two good fire extinguishers. Fortunately, I've been lucky in never having to use them on my own cars but on a couple of occasions they have come in handy for other motorists to use. Thanks again Rod Quote Link to post Share on other sites
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