Richard Pope Posted October 25, 2020 Report Share Posted October 25, 2020 I’m adding a J type overdrive unit to my USA spec J type gearbox. The USA spec gearbox has a ‘neutral’ switch as well as a reversing light switch. In fact this ‘in neutral’ switch only senses if one is in 1st or 2nd (presumably safety assumes one can never start the engine in 3rd or 4th). So with a simple circuit I can inhibit the O/drive engaging in 1st, 2nd and Reverse. This removes all hassle in locating position, adding a 3rd / 4th switch, drilling, tapping, etc, especially as each selector picture I look at has a different switch location. The two switches appear very simple spring plunger triggered on/off but I cannot get a continuity in either of them. OK, both could have failed but surely unlikely. They appear non-damaged and spring plunger feels fine. Question. Are they just a simple switch with plunger down against spring = Off / no continuity? Yes, cheap to buy replacements but am I missing something? I’m puzzled! Quote Link to post Share on other sites
stuart Posted October 25, 2020 Report Share Posted October 25, 2020 Quite often those switches suffer a bit of corrosion on the contacts inside, they are easy enough to carefully ben the tabs up and open them up. Clean the contacts and remove the old dried out grease and re-grease and fit back together and they will last for years. Stuart. Quote Link to post Share on other sites
SpitFireSIX Posted October 25, 2020 Report Share Posted October 25, 2020 It will not help using a Multimeter that can only push a couple of mA at best. Try checking with 12v and a 21/5 Watt lamp as a load. Quote Link to post Share on other sites
Waldi Posted October 26, 2020 Report Share Posted October 26, 2020 I measured the resistance with a simple multimeter. I was surprised how many switches were not ok. Contact spray fixed most of them. Checking resistance is a better way to check switch condition that a lamp, i feel, especially if you activate the switch several times and check if the readings are consistently low. Waldi Quote Link to post Share on other sites
Mike C Posted October 26, 2020 Report Share Posted October 26, 2020 Clean with contact cleaner then check with a multimeter. Some people might not agree, but if a switch sticks I lube it with silicon lubricant then confirm it's still working afterwards with the multimeter. Quote Link to post Share on other sites
Richard Pope Posted October 26, 2020 Author Report Share Posted October 26, 2020 Thanks. OK, I'll open them up and nothing to lose anyway. I had wondered if oil had got inside and caused the problem. We shall see. Quote Link to post Share on other sites
SpitFireSIX Posted October 26, 2020 Report Share Posted October 26, 2020 14 hours ago, Waldi said: I measured the resistance with a simple multimeter. I was surprised how many switches were not ok. Contact spray fixed most of them. Checking resistance is a better way to check switch condition that a lamp, i feel, especially if you activate the switch several times and check if the readings are consistently low. Waldi An old analog type meter might be better than a DVM. DVM tests at very small currents. 1mA. I have never had a problem using a DVM. Quote Link to post Share on other sites
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