Coil Wiring

[CaptDon01]

On my TR3B, still negative ground, my Lucas coil is marked "CB" on the side that connects to the wiring harness, and "SW" on the side which runs to the dist. Anyone know which side would be the + and - sides for a negative ground system?

Thanks,

Don

 

[LastDeadLast]

Have you seen this?

https://www.advanceautowire.com/tr24a.pdf

 

[Don Elliott]

Don - You write "still negative ground". My TR3A has always been positive ground.

Don Elliott, Original Owner, TS 27489 LO

https://www.britishcarforum.com/ubbthreads/photopost/showphoto.php/photo/1977/cat/517

 

[CaptDon01]

My mistake.....my TR3 still has the positive ground....

Don

 

[Andrew Mace]

[ QUOTE ]
On my TR3B, still negative ground, my Lucas coil is marked "CB" on the side that connects to the wiring harness, and "SW" on the side which runs to the dist. Anyone know which side would be the + and - sides for a negative ground system?

[/ QUOTE ] The "CB" is for Contact Breaker (points), which go to ground. The "SW" is for switch...the "hot" side. If you stay with original positive ground, then "CB" is + and "SW" is -. If you change to negative ground, reverse those two. {Apologies for my mistyping before; the above is now corrected. Thanks for catching my mistake!}

 

[Keoke]

NO Andrew. If the car is POS GND then CB goes to the Dizzy and SW goes to the IGN SW. Or CB=+ and SW=- .___Fwiw---Keoke

 

[Geo Hahn]

i.e. Capt Don... yours is connected backwards... and it does matter. The engine will run fine for awhile like that but the points will soon be roasted.

 

[Keoke]

HI GEO, HE Jest might roast the Rotor, Distributor cap and High tension leads too.---Keoke /ubbthreads/images/graemlins/laugh.gif

 

[CaptDon01]

OK....I just checked my TR3B which has + ground, and as best I know, it's the original coil, and the points and condenser have been in for years, and are in good shape. The white wire from the ignition switch goes to the coil terminal marked "CB", and the other coil terminal is marked "SW", which is a white wire with a black tracer, and it runs to the distributor. The reason I'm asking is that I met a local guy with an unbelievable original 62 TR3B, (TCF 530 L). It's been in his family since new, and only has 40K miles on it! He was doing a tune-up and couldn't get any spark. The coil that was on it was a replacement, and it checked open from the + to the - terminals. He bought a new coil, and it is also marked + and - . I was checking his ignition over, and we get 12 volts to both sides of the coil, and to the terminal in the distributor when the ignition is on. But there is no spark from the secondary side of the coil, and when you turn the engine over, no slight spark as the points open and close. If you check a coil with an ohm meter, what resistance readings should I get between the low voltage terminals, and the low voltage terminals to the high voltage side?

Thanks for the answers, I hope I didn't confuse anyone.....

Boy, this guy has a GEM of a TR3B....everything original, still has all the tool kit, the felt pad in the trunk, and there is still red paint inside the wheel wells!!!!! Absolutely NO rust!!!!

Thanks again,

Don

 

[Dave Russell]

[ QUOTE ]
OK....I just checked my TR3B which has + ground, and as best I know, it's the original coil, --- The white wire from the ignition switch goes to the coil terminal marked "CB", and the other coil terminal is marked "SW", which is a white wire with a black tracer, and it runs to the distributor. --------- I was checking his ignition over, and we get 12 volts to both sides of the coil, and to the terminal in the distributor when the ignition is on. -------- If you check a coil with an ohm meter, what resistance readings should I get between the low voltage terminals, and the low voltage terminals to the high voltage side?
Don

[/ QUOTE ]
Hi Don,
As Andrew, Keoke, & Geo said, your coil is connected backward. The terminal marked "CB" (contact breaker) should go to the points & the terminal marked "SW" (switch) should go to the ignition switch. It really won't hurt much of anything but the spark plugs will require about 20% more voltage to fire with this connection. I guess this could put additional voltage stress on the rotor, cap, & wires. For a negative ground system with this same old coil, the connections would be reversed.

If the points are open, you would read 12 volts on both sides of the coil. (CB & SW) With the points closed you should read near zero volts on the points side & 12 volts on the supply side.

The Ohmmeter should read around 3 Ohms between the two small terminals, & 7,000 Ohms from either small terminal to the center high voltage terminal.
D

 

[CaptDon01]

Thanks guys.....just want to make sure I've got it right then.....SW = negative and CB = positive. (for a positive ground car)

Thanks again!!!

Don

 

[dklawson]

Minor addition to Dave's closing paragraph above. Mark and disconnect the low tension wires from the coil when measuring across the two small terminals. If you don't remove the low tension wires you may be measuring the resistance of other components on the car while you're trying to measure the coil.

Make the coil connections as Dave and Keoke said. In the case of a positive ground car, a later coil should have its (+) terminal connected to the dizzy/points and the coil(-) terminal should be getting supply from the ignition switch.

You can test the coil w/o the distributor. Remove the low tension wire from the dizzy side of the coil. Place one of your regular spark plug leads (with plug) in the center (tower) terminal of the coil and rest the spark plug on the block. With the ignition switch turned on and a jumper wire on coil (+)... tap the free end of the jumper to the chassis of the car. Remember, tap, not hold. You want to make and break the ground connection with the jumper to simulate the points opening and closing. If your coil is operational this will give you healthy sparks on the plug.