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MG TD TF 1500 - Coil Wires

When I discovered my TD was switched to negative ground, I had read several threads about switching coil wires. Seemed to be optional. However, months later when I was researching a sooty exhaust, I came across a connection to the coil wiring. I believe it was Bob Jeffers that said you won't get full spark if you do not have the coil/distributor polarity correct.

From what I read, the coil wire (I have no colors left, so wire colors mean nothing to me :-) should go to the ground side of the coil. Mine was still hooked to the + terminal of the coil, so I switched it to the - terminal and the wire from the harness on the + terminal. Just confirming that this is correct. Thanks.

Larry

L Karpman

Sorry, meant to say, "the distributor wire should go to the ground side...."

Larry
L Karpman

Larry - For a negative ground car, the wire from the distributor should go to the terminal marked SW (or -) and the wire from the ignition switch should go to the terminal should go to the terminal marked CB (or +). This is assuming that you have an original coil, or a coil intended for a positive ground car. Let me know if you have a different coil and I'll dig out the information that I have on determining what coil you have. Cheers - Dave
David DuBois

Dave:

There's not a single identifying mark on the coil. I'd have to say it looks to new to be original. Just the small +/- on the plastic front.

I will say this, the car doesn't seem to run any better, and it is harder to start since I swapped. makes me think it was correct before.

Larry
L Karpman

Larry - With the + / - on the coil you should have the + terminal attached to the ignition switch and the - terminal to the diatributor for a negative ground car. You may have to re-time the ignition a bit to correct the hard starting, since you are now triggering on a positive going pulse rather than a negative going pulse, but I've not heard of that before. Cheers - Dave
David DuBois

In some cases the bottom of the coil case will be stamped with markings such as "L12" or some such. Sometimes with a date.
J Delk

Thanks Dave. It gets more interesting by the minute. Car starts and runs better hooked up backwards. I'm not savy enough to understand your "positive going pulse rather than a negative going pulse" but I'm suspect of the points, as perhaps one of the contacts is more coated than the other and changing the direction has brought that into play. That would make sense to me. Going to check tomorrow.

I'd like to run a hotter spark no matter what, as the car runs a little rich, and my mech said that he has adjusted the carbs to their limit right now. I was looking at the Lucas Sports Coil, as I have no other reference for a hotter coil for the TD other than Moss, etc. I realize that these type coils shorten the life span of other components to some degree, so I was wondering of the experiences of those in the group that use them. Benefit and drwback answers would be greatly appreciated. Thanks.

Larry
L Karpman

Carbs a bit rich?

Lower your fuel level in your float bowls by dropping your floats a tad (bend the tab in the float bowl lid so the float rises slightly less before the needle valve is shut). Fuel level should be 1/8 to 3/16 inch below the bridge... tough to see, but lowering the fuel level should allow you to drop your jets a couple of flats and achieve a proper mixture. The starting point for our carbs is six flats down on the mixtures. If you are all the way up, you don't have any adjustment.

warmly,
dave
Dave Braun

Thanks Dave: I don't want to throw this thread off the "coil" track, so can you send your email address to me at:

lkarpman at tx dot rr dot com. I have a carb question or two if that's OK.

Larry
L Karpman

L. Karpman -- I've been running the Sports Coil marked SP-12. The primary resistance is 3.2 ohms. The turns ratio is 89.1 (original TD coil was 48.7). Now because the coil gives me more voltage I run NGK plugs
BR6HS-10 (see article in the Oct. 97 TSO ). These are resistor plugs and come with a gap of .035" and I run with that. Engine starts so fast it will scare you. The negative is that the rotor I had in there at first broke down and developed an internal short to the cam. The one thats in there now has been there two years so far so good. Also the points have to switch more current so I am running pertronix ignition. Haven't had to touch the timming in 3-4 years.
Hope this helps.
Cheers,
Bob
R. K. (Bob) Jeffers

Larry, see http://www.ttalk.info/Tech/pertronix_igniters.htm.
Bud Krueger

Thanks Bob and Bud. Yes Bud, I have seen your great Pertronix page and instructions before. I am considering the Pertronix, but need to know the difference between the two that Moss has.

As for the Sports Coil Bob, I assume that the SP-12 pre-dates the current Lucas DLB105. What would be the reason to choose one over the other? Also, I have run NGKs in my Jag V12, and have always been happy with them, but alas I have no access to the TSO articles. If I were to set mine up as yours, would timing need to be adjusted. Without a crank to get to TDC to start, I'm a bit handicapped in that regard right now.

I have the Lucas Bumble Bee wire on my shelf, and that is one of this weekends projects to swap over my ignition wiring to that. A good start I believe.
L Karpman

L Karpman -- To choose between the SP-12 and the DLB105 I would guess that you have to make a decision, do you want the latest and newest or a period assessory? The period assessory may be old and tired and quite on you while that is unlikely with the modern part. Your choice.

The SP12 is a coil with an aluminum case, a brown plastic high voltage terminal that has ripples in it to give a longer path to prevent arcover's. Also had the screw-in type connector for the coil output. Mine had the Lucar connectors on it for the distributor and ignition connections. I made some adaptors to use the TD type ring terminals. So I did not have to modify the harness.
Cheers,
Bob
R. K. (Bob) Jeffers

Larry, put the car in top gear, and with the spark plugs out, push the car foward in lieu of a crank, to find TDC (a helper will be handy in this case)

warmly,
dave
Dave Braun

Thanks Dave. I managed to use 2 hands to move the pully to TDC.

Larry
L Karpman

You're right Bob. I didn't even think of the DLB105 not accepting the Lucas screw on connectors and having to modify that end for a push on. That said, I have no idea where to look for a SP12. A/S has a "Lucas Sports Coil, Original" for a whopping $95!!

Larry
L Karpman

This thread was discussed between 12/12/2006 and 14/12/2006

MG TD TF 1500 index

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