Inductive Timing Light Won't Fire - Help?

[tom1394racing]

Getting ready for the first drive on my '70E restoration project. The engine is in the car and has been run in for 20 minutes at 2000 RPM. Seemed to run just fine. Smooth, no funny noises or leaks. Did the first oil change and decided to check the timing using my trusty Craftsman inductive light with dial in advance settings. This light has always worked well for me on my '73 and previous cars. Hooked the negative to the coil stud ground, the positive to a terminal on the 3 pin fuse and clamped the inductive lead to the #1 spark wire. No flash on the light. I double checked for 12 V to the positive and neg leads to the light and also tried another plug wire. Still no flash on the light. I also tried powering the light with my 12V power supply. Still no flash. It had been about 2 years since I had used the light so I fired up my '73 and connected the light as I always do and it worked like it should. I also put an in line spark detector on the # 1 plug wire on the '70 and it flashed as it should.

Anyone have any idea what my problem is? Are there certain types of plug wires that will not fire an inductive light? Could my spark be too weak to fire the light?

[xpensivewino]

That is odd Tom. My intuition would say it’s an issue with the positive lead to the fuse. I’m not sure why but not much could go wrong with the other connections. Perhaps try a different source for the positive?? You’ve verified spark to number one? Steve

[tom1394racing]

I verified power to the three pin fuse panel separately with my multimeter. I even tried powering my timing light with my separate 12 V power supply. I verified spark number to one with an in-line spark detector. And I tried the inductive timing light on other ignition wires. No flash at all. Very odd. Particularly considering that the engine seems to run really well......smooth, no backfiring, accelerates up the rev range. I haven’t driven the car yet. So I really haven’t put the engine under any load.

I am thinking that possibly I might just have too weak a spark to trigger the inductive timing light but enough spark to run the engine. Everything in the ignition system was rebuilt except I’m using an original used Bosch black CDI coil. I checked the coil resistances both primary and secondary and they were right within spec. I guess I might try an new MSD blaster coil and see if that makes a difference.

Any other ideas???

[xpensivewino]

Try swapping the coil from the 73 and see if it makes a difference, also swap the plug wire for number 1 from the 73 provided it’s not a CIS wire. That should eliminate several variables.

[tom1394racing]

My thoughts also...Thanks

[ejboyd5]

Double ditto on a trial swap of spark plug leads.

[edmayo]

Sounds to me like you have a bad light ! I have seen the wire connection in the inductive pick up break,,,take the induction clamp apart and see if anything obvious.

[tom1394racing]

Ed...I tried the light on my ’73. It worked fine. That car has an MSD system and solid core wiring. Would that make a difference?

[edmayo]

Not really, inductive should work on either solid core or resistance core. But as an aside, I thought MSD wanted resistance plug wires? I can't see that if there is enough spark energy to run the engine that it wouldn't be enough to fire the light. Just for grins try a different ground point, I use the motor mount bolt since that is close to the fuse panel. I know, sounds silly, but give it a try.

[tom1394racing]

But as an aside, I thought MSD wanted resistance plug wires?

Yes Ed. The wiring on my '73 is spiral core. Not solid core