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TR6 TR6 / Pertronix / Ballast Resistor / etc

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brucebotti

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I've got a few questions for you experts. I'm installing a Pertronix in my 1974 TVR (TR6 motor).

1. Is it okay to use the Lucas Super Coil? It seems to read 3.0 ohms which means it should be okay.

2. My coil has two leads on the + side of the coil. I can't find (see) a ballast resistor, but the voltage reading at this point is 9.3v with the ignition on, about 8.6v while cranking, and 12.2v once started. Does this sound normal? Both wires are the same color, a greasy beige. I can't really trace them without an enormous amount of work.

3. Do you think I can hook up the Pertronix as is?

Thanks in advance!
 
I have been running Pertronics successfully for a year with the Lucas Sports coil, but I didn't read those instructions.
Either I'm running on luck or they are compatible.
 
Thanks Doug. I figured that they would be compatible. I just wish I knew what the two wires on the + side of the coil were. I know one is either from the ignition or the ballast resistor. Sure wish TVR had a reliable wiring diagram /ubbthreads/images/graemlins/confused.gif
 
Bruce, for the TVR one wire comes from the starter solenoid and the other comes through the ballast resistor. This provides unballasted voltage when cranking and ballasted otherwise.

edit: On my car the ballast resistor is on the passenger side below the heater box. See a photo below.

ysmgreen.jpg
 
Thanks Hayden. I don' see a ballast resistor, unless its hidden really well. I'll go back for a second look. The strange thing is that my voltage reading is 9.3 v with the key on (not running), 8.6v while cranking, and 12.2 while running!? Almost like an un-ballast resistor /ubbthreads/images/graemlins/confused.gif!
 
I may be fuzzy on this but I think my 74 TR6 has a resister wire; you cannot see a resister because it looks like a regular wire.
 
Typically a ballast resistor will drop the voltage to 6 volts at the coil while running, while leaving it a full 12 during start. If you have 8.6 cranking volts (measured where?) then you likely have one of three issues. The starter has high resistance, the battery is weak, or one of the battery cables has high resistance from crud inside it.
 
As mentioned above, a lot of Lucas wired LBCs with ballast ignitions use a resistor wire (typically pink) from the ignition switch to the high-side of the coil. You may not find an external resistor.

WARNING: There are a couple of things you have to be careful with when working with Pertronix. First: Do not leave the ignition switch on for prolonged periods without the engine running. The chip in the Pertronix will overheat. (Ignitor II is different and not affected by this) Second: Use the right coil/wiring as you noted. If the current flow through the Pertronix module is too high you'll cook it.

You can run a non-ballast coil on a ballasted ignition system but it will have a weak spark in normal 'run' mode. Since you have a volt meter, set it to ohms. Disconnect the coil (+) wire coming FROM the ignition switch. Connect one end of the meter to the wire you disconnected from the coil. Connect the other meter lead to the fuse box and switch on the ignition. This will allow you to measure the resistance of the wire supplying the coil. (DO NOT mistakenly connect either meter lead to ground or you'll give the meter a power-enema and its white smoke will leak out). If this measurement shows something close to 1.5 ohms, you have a resistance element somewhere between the ignition switch and coil and you need a ballast ignition coil. (Be sure to check the resistance of your meter leads to each other... mine measure about 0.6 ohms and this would be subtracted from the total measurement). Note in your Pertronix instructions that ballast ignition systems require you to connect the red wire to a full +12V switched source, not to coil (+).
 
Bruce, what's your chassis number again? My parts guy's 77 had the same green ballast resistor as my 74 (I know this because he sent me a NOS one for free saying it's TVR only, TR6's didn't use it and I was his only TVR customer at the time). You might check the passenger side tunnel area pictured for the little clamps in my picture that hold it, it could have been bypassed by a DPO or something.

edit: the 8.3V while cranking is kind of meaningless, because that same current running through the ballast could be 5V or something, that starter can draw a lot of current. Also, if you look at the starter there are 2 small wires connected. One comes from the key and the other is white and goes to the coil. Try disconnecting it and see what your voltage is when you crank then, that will help tell if you have a ballast in the system.
 
Thanks guys.....you've givenme food for thought!

Hayden, my chassis # is 3054TM....I'll look a little closer as my crazy work schedule allows.

Bruce
 
Hayden,
Thanks, but no need to bring the Fluke on my account. I'll have it sorted out by then....just need to get the time to work on it. See you at Carlisle!
 
I just completely bypassed the stock harness (with resistor wire) and came straight off the fuse block with a dedicated wire for the Sport coil.


Bill
 
Thanks guys. Got the Pertronix / Lucas Coil in and evrything is runnin fine.

Next question....how far do you open up the plugs with the Pertronix. I know you can open the gap, just not sure how much.
Thanks!
 
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