billy l Posted December 17, 2009 Report Share Posted December 17, 2009 Hi Guys, I am going to change the polarity on my TR3 to neg earth, I know about changing the leads around on the ammeter and coil and changing the polarity on the dynamo, but I am sure that I read in TR action some time ago that the fuel gauge leads also needs to be swapped around. Is this correct or did I just dream it? I'm sure all you electrik boffins out there will know the answer. Thanks for your time, Bill. Quote Link to post Share on other sites
ianc Posted December 17, 2009 Report Share Posted December 17, 2009 Hi Guys, I am going to change the polarity on my TR3 to neg earth, I know about changing the leads around on the ammeter and coil and changing the polarity on the dynamo, but I am sure that I read in TR action some time ago that the fuel gauge leads also needs to be swapped around. Is this correct or did I just dream it? I'm sure all you electrik boffins out there will know the answer. Thanks for your time, Bill. Yes, on the TR2/3, one needs to swap the connections on the fuel gauge as well as the ammeter. Not necessary on the TR4 because that model has a hot-wire type of fuel gauge. See Section J4 of Technicalities CD which, in the preamble to the description of changing to an alternator, I mention the changes required to the instruments. Ian Cornish Quote Link to post Share on other sites
Andrew Smith Posted December 17, 2009 Report Share Posted December 17, 2009 Hi Bill, Have a look at Teri Ann's site: http://www.tjwakeman.net/TR/polarityConversion.htm Cheers Andrew Quote Link to post Share on other sites
billy l Posted December 18, 2009 Author Report Share Posted December 18, 2009 Hi guys, thanks for your replies, now I have a problem, Ian's reply says the leads are to be swapped but andrews reply says not. What do I do Hellllllp! Quote Link to post Share on other sites
ianc Posted December 18, 2009 Report Share Posted December 18, 2009 Whoops - I had forgotten about the coil (which is mentioned by Teri) - that does require its connections to be swapped or you will have problems with the engine (it won't run very well as the sparks will be jumping in the wrong direction at the ends of the plugs). That's something I missed when I wrote my article back in the 1970s. I haven't got a TR2/3 to hand to be able to check on the fuel gauge, but the gauge is measuring a small current, which is under the control of a variable resistor in the tank's sender unit. Hence, if the leads were not swapped at the gauge, the needle would be driven in a negative direction (i.e. below empty). So, I'm sticking to my guns on this one! Mind you, if I were wrong, the gauge is very accessible! Ian Cornish Quote Link to post Share on other sites
Andrew Smith Posted December 18, 2009 Report Share Posted December 18, 2009 Billy I'm rewiring TuRK over the Crimbo period (pos earth) and me and 'electrickery' don't necessarily get on that well, so wish me luck! Anyway, I'm sure 'Trevor S' will not mind me sharing this negative earth wiring diagram he sent me for a neg earth conversion - hope it helps? Cheers Andrew Quote Link to post Share on other sites
mike ellis Posted December 19, 2009 Report Share Posted December 19, 2009 I have recently changed my TR3A to negative earth, but did not swap the fuel gauge leads. The gauge still reads correctly. Quote Link to post Share on other sites
ianc Posted December 20, 2009 Report Share Posted December 20, 2009 Thanks, Mike, that's very useful - but puzzling! I'll have to think why this should be. Ian Cornish Quote Link to post Share on other sites
TR 2100 Posted December 20, 2009 Report Share Posted December 20, 2009 (edited) I have recently changed my TR3A to negative earth, but did not swap the fuel gauge leads. The gauge still reads correctly. Thanks, Mike, that's very useful - but puzzling! I'll have to think why this should be. Ian Cornish I guess if the tank is empty . . . . . .?! To change the polarity, don't you also have to change the polarity of the generator - easy enough, I recall, but being worse than useless with electrics, I won't try to explain. AlanR Edited December 20, 2009 by TR 2100 Quote Link to post Share on other sites
foster461 Posted December 23, 2009 Report Share Posted December 23, 2009 Hi Guys, I am going to change the polarity on my TR3 to neg earth, I know about changing the leads around on the ammeter and coil and changing the polarity on the dynamo, but I am sure that I read in TR action some time ago that the fuel gauge leads also needs to be swapped around. Is this correct or did I just dream it? I'm sure all you electrik boffins out there will know the answer. Thanks for your time, Bill. I dont know anything about polarity but I was stung by a bee while following a TR3 this summer (sorry, those other people made me do this) Quote Link to post Share on other sites
ianc Posted December 23, 2009 Report Share Posted December 23, 2009 I dont know anything about polarity but I was stung by a bee while following a TR3 this summer (sorry, those other people made me do this) This is an apology from Cornish regarding the fuel gauge on the TR2/3/3A! I consulted Tony Thomson and he reminded me (golly, I ought to have remembered!) that moving iron meters are NOT polarised, and can be used on direct or alternating current, always reading in the same direction. Hence, the connections to the fuel gauge - a moving iron meter - do not need to be reversed (but if they were, it would make no difference to the reading!). The ammeter is a moving coil meter, hence is polarised and MUST have its connections reversed. Tony has added some useful information about the coil, as follows: According to Tony Tranter in Haynes "Automobile Electrical Manual", ignition systems are designed to have negative polarity at the centre electrode and if reversed can be up to 40% less efficient. Coils for both Positive and Negative earth vehicles were produced, but who would know if anyone has changed a coil for the wrong type in the history of older vehicles, so it is wise to check polarity of the spark (see below for testing polarity using a lead pencil). With early coils, swapping the CB and SW leads will switch polarity of the spark. Later coils are marked + and - but the requirements are the same. To test the spark direction with a lead pencil, interpose the writing tip of a lead pencil between the spark plug top stud and the HT lead, leaving a small gap either side of the pencil tip. If the polarity is correct, a flare between the pencil and the spark plug will be seen as the engine is cranked. If the flare is between the pencil tip and the HT lead, then the polarity is reversed. Since all modern vehicles use a negative earth system, almost all replacement coils will be marked +/- and will expect the vehicle to be negative earth. Almost all in-car entertainment systems are designed for negative earth, as are almost all in-car electronic devices. There may be validity in keeping a positive ground in an older vehicle for the sake of authenticity, but if it has any modifications, switching to negative earth is to be highly recommended. Thanks, Tony, for teaching Grandpa to suck eggs! Ian Cornish (now where did I put that darned rocking chair?) Quote Link to post Share on other sites
tthomson Posted December 23, 2009 Report Share Posted December 23, 2009 Thanks, Tony, for teaching Grandpa to suck eggs! Ian Cornish (now where did I put that darned rocking chair?) No problem Ian! I hope it is useful to others out there in TR land Meanwhile Happy Christmas and New Year to all of you. Anyone have any suggestions for another TRAction article - I had one person suggest a delay wipe system, and I have a working design. Any interest? TT Quote Link to post Share on other sites
TR3BGeorge Posted December 23, 2009 Report Share Posted December 23, 2009 I dont know anything about polarity but I was stung by a bee while following a TR3 this summer (sorry, those other people made me do this) AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH!!!!!!!!!!!!!!! Quote Link to post Share on other sites
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