Triumph Repair: TR5 hot starting problem, ballast resistor, triumph tr 7

Question
My TR5 (fuel injected)has always overheated in standing traffic, the solution for which I know is possibly the electric fan! However, I've just fitted the Pertronix electronic ignition system (supplied by Moss) to the car and it starts and runs fine at normal temperature. However, when it gets hot in traffic, is turned off when stopped and eventually restarted(very reluctantly)it comes to dead halt in about 300m. Lifting the bonnet reveals a very hot coil (attached to the block as normal,)which when cooled with cold damp rag allows normal service to resume, until the next traffic jam of course!!! The coil is also a new one from the same supplier. Any ideas???

Answer
Hi Peter,

I don't have a diagram of the TR-5 and even though I worked for many years in Triumph dealerships in Florida USA, I only seen one TR-5. So I don't remember what coil was used. However, all cars back it those days did the same thing. They either used a 12v coil or a 6v coil with a ballast resistor and a bypass circuit to power the 6v coil directly with 12v only in the "Start" position.

All coils operate the same way and that is, points close and ground the coil in the distributor (or an electronic ignition system grounds the coil) The coil needs to be grounded to build a electronic field inside the coil. Then when the circuit is broken either by points or by an electronic ignition. The field then collapses and the field transfers to the secondary in the coil, which is connected to the coil wire, cap and spark plug where the field jumps to ground thus a spark.

Some electronic ignition systems require a 6v coil. Which then require a ballast resistor and some even require a power resistor also. The Triumph Spitfire and the Triumph TR-7 both use two resistors. The ballast resistor is used to drop the voltage to the coil and the power resistor is used to drop the voltage to the electronic ignition system.

If a 6v coil is used without a resistor the coil overheats which will destroy a coil. If a diagram didn't come with the Pertronix system, you need to contact Moss Motors to find out how it must be wired and what coil needs to be used and what resistor to use.

As far as the cooling system over heating in traffic, I found while working in Florida that almost all of the old British sports cars did overheat in traffic and I agree with you on the added electric fan. I always added the electric fan in front of the radiator to blow through the radiator and leave the original fan on too.

Be sure to check the thermostat for it's temp rating and to see that it operates at the correct temp.

Howard