StevedTR4A Posted June 5, 2011 Report Share Posted June 5, 2011 Hi all Can you help clarify please. My 1959 3A is poitive earth. 1950's Lucas service literature states that its coils are wound for positive earth. I have a new Lucas DLB100 coil as a spare and in a recent Lucas specification sheet it states that it is for TR2's and TR3's. I am aware that these newer coils have + - on the cap rather than CB and SW. Also from previous threads that for positive earth cars the + terminal should be connected to the distributor. Does this mean that these newer DLB 100 coils are still wound for postive earth? Steve Quote Link to post Share on other sites
Ashley James Posted June 5, 2011 Report Share Posted June 5, 2011 I don't think it can matter which way round they are connected, but if a car is positive earth I always put the postive to the distributor (which means to positive) and the negative to the ignition switch. Ash Quote Link to post Share on other sites
Ian Vincent Posted June 5, 2011 Report Share Posted June 5, 2011 Years ago when I had an A-H 3000 it was positive earth. I wanted to fit a radio/cassette player and they didn't make them with anything other than negative earth. It was a half hour job to swap the battery terminals, swap the coil and reverse the residual polarity of the dynamo field coils by sparking it on the battery - job done and henceforth the car was negative earth. Same coil, same everything in fact - as far as I am concerned there is no difference in a coil for +ve or -ve earth. Rgds Ian Quote Link to post Share on other sites
StevedTR4A Posted June 5, 2011 Author Report Share Posted June 5, 2011 Thanks Ash and Ian, Good to know Steve Quote Link to post Share on other sites
ianc Posted June 5, 2011 Report Share Posted June 5, 2011 If a coil is marked +/-, then at the coil the positive must be positive and negative must be negative! If the car is a TR2/3/4 with positive earth (i.e. not converted for use with an alternator), then the feed from the ignition switch should go to the -ve on the coil, and the distributor should be connected to +ve. If the coil is connected the wrong way about, the spark (HT side) will be trying to jump the wrong way and the power output, performance and fuel consumption will suffer. You can find more information on this subject on the Forum by doing a Search. Ian Cornish Quote Link to post Share on other sites
kiwi-jim Posted June 6, 2011 Report Share Posted June 6, 2011 Thats the great thing about this Forum, i have just been playing round with the timing on my car because I wasnt particularly happy with it, and following your post Ian, i checked and found I had my coil wired up the wrong way round, I know previously fuel cnsumption was very poor and running not 100% it will be interesting to see what happens now i have changed te leads over. Thanks for spelling out whats required otherwise i would probably still be running round with the wires back to front. cheers Jim Quote Link to post Share on other sites
StevedTR4A Posted June 6, 2011 Author Report Share Posted June 6, 2011 Thanks Ian That explains all. Steve Quote Link to post Share on other sites
John McIver Posted June 10, 2011 Report Share Posted June 10, 2011 Like kiwi-jim, I too checked the terminals on the Bosch coil fitted to my TR by a PO. The car is wired as original with +ve earth and, sure enough the power lead was on the +ve terminal. All this after I had replaced the complete loom some months back and had simply reconnected the leads as they were. One never stops learning. Thank you Ian. Quote Link to post Share on other sites
ianc Posted June 12, 2011 Report Share Posted June 12, 2011 I knew that the ever-helpful Tony Thomson had sent me information some 18 months ago on a simple test for coil operation, but it was only last night that I remembered where I had buried it - don't laugh, you'll suffer this problem when you're in your 70s, but at least I remembered eventually! So, for the record, here it is: "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 (if the flare is between the pencil tip and the HT lead, then the polarity is reversed)." Thanks once again, Tony, Ian Cornish Quote Link to post Share on other sites
TomMull Posted June 13, 2011 Report Share Posted June 13, 2011 If a coil is marked +/-, then at the coil the positive must be positive and negative must be negative! If the car is a TR2/3/4 with positive earth (i.e. not converted for use with an alternator), then the feed from the ignition switch should go to the -ve on the coil, and the distributor should be connected to +ve. If the coil is connected the wrong way about, the spark (HT side) will be trying to jump the wrong way and the power output, performance and fuel consumption will suffer. You can find more information on this subject on the Forum by doing a Search. Ian Cornish Ian, I always thought it went p tp p and n to n on the coil regardless of earth polarity. Have I had it wrong? Tom Quote Link to post Share on other sites
ianc Posted June 13, 2011 Report Share Posted June 13, 2011 Tom: Yes + to + and - to -. However, remember that in an unconverted TR2/3/4, + on the battery is connected to earth (bodywork). So, if the coil is a modern unit marked +/-, then - must be fed from the ignition and + should be connected to the distributor so that, as the contact breaker closes, this end will be positive (i.e. earthy). Ian Cornish Quote Link to post Share on other sites
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