Triumph Repair: starter solenoid perhaps, starter solenoid, triumph spitfire

Question
Hello Howard,  I have a 1965 Triumph Spitfire equipped with the starter solenoid with the test button to start the car from under the hood. This works fine, and the starter motor spins fine, and the car starts with the ignition turned on.  But when I attempt to start the car with the ignition key, intermitently, the starter will not operate, have you any suggestions...solenoid or ignition switch; or maybe something else...?

Answer
Hi Kevin,
Intermittent problems are the hardest to find unless you add a monitor to be able to see when current is not going where it is suppose to.
Attach a small wire to the connector with the White wire with a red stripe on it on the solenoid and run it out from under the hood and attach a test light to the end of the wire and ground the lead of the test light. Tape the test light to a wiper blade so you can see the light from in the car. Be sure the wire is not pinched anywhere along the rout. Now, every time you turn the key to start, you will see the light come on. When you get your failure, note the test light. If it is on as usual then the solenoid is failing. If you have no light than you need to test the same at the ignition switch. (white with a red tracer)
let me know how you do.
Howard