QUOTE(targa72e @ Aug 15 2022, 12:54 AM)
New cars never touched by me are assumed to be perfect
Just saw a newish Jeep Gladiator going on the flatbed yesterday - blocking traffic of course.
As you've noted, new cars don't guarantee that they will never be on the back of a flatbed.
Quite the opposite. A failed crankshaft sensor will leave you walking without warning. They go from OK to Not OK in a fraction of a second. I use that as only one example of where modern electronics can fail and leave you stranded.
Old (pre-80's) cars on the other hand, I can usually jury rig a solution to get me home.
A few examples:
Broken throttle cable -- replaced by using shoe laces tied together to pull the throttle linkage by hand.
Broken clutch cable -- creative shifting to avoid stopping. Having to start the car in 1st gear at the few lights I couldn't time or get though on a slow roll. Not good for the starter or battery but got me there.
Distributor center cap with failed carbon button. This was the only instance I've ever had on a carburated car where it just quit running without warning. Solution: Jammed some copper wire into the button pocket just about long enough to touch the rotor. It was misfiring bad but got me there.
Don't get me wrong, modern cars have a lot of advantages but jury rigging a fix to get you home is a whole lot harder than it used to be.
Moral of the story: Go drive that 914 on long trips!
To answer OP's question. VIntage CDI not easily tested DIY. Due to components inside the box (vintage switching components SCR/thyristor/transistors, and aging capicitors) CDI is subject to instantaneous failure just like any electronics on modern vehicles. Even if it tests OK today, a vintage component inside the box may fail tomorrow. If it were me, I'd replace the 50 year old part, putting it aside for someone concerned about originality, and replace with a more modern CDI that doesn't have 50 years of age / use on it. Modern electronic components like SCR's/Thyristors/Transistors/MOSFET's are generally more robust & durable than vintage components that perform the same function.
Here is a simplified schematic of what a CDI is (this is a motorcycle application with the stator supplying excitation to charge the capacitor)
Click to view attachment If this diagram has no meaning to you - move on. DIY testing is not for you.
If you want more info on actual Bosch CDI start at this link for more info.
http://forums.pelicanparts.com/porsche-911...schematics.html