timing light with 4 leads

[Daves55Sedan]

My neighbor has a static timing light (not an inductive one) that has FOUR wires and alligator clips. Red (+) to battery, Black (-) to battery, Yellow to #1 spark plug....ANNNND a second black wire with alligator clip.
The timing light is relatively small, shaped like a gun, has a black plastic housing with a white pushbutton on the back of it. There is no identification of any kind on it.
I have only EVER seen several timing lights of both types with THREE leads.
Anybody know what the second black lead and alligator clip is supposed to go to???

 

[KULTULZ]

Never seen one (I don't think). I bet someone at HAMB would know. They have a few guys older than me over there ...

 

[craig]

So, if it's not inductive, the yellow goes to the spark plug, then the 4th wire would have to connect to the spark plug wire....maybe?

 

[Daves55Sedan]

So, if it's not inductive, the yellow goes to the spark plug, then the 4th wire would have to connect to the spark plug wire....maybe?

The older static timing lights came with a reducer spring that allowed connecting the large end of the spring to the spark plug, while the small end would have the spark plug boot plugged into it. Then you clipped the alligator clip from the timing light around that spring. What good would it be to have a second wire for the spark plug?

 

[Daves55Sedan]

I've been using timing lights since the early '70's and they have all had 3 leads. My first timing light was a static type. When I got my first inductive timing light in the late 1980's, I loved it because it doesn't require removal of the spark plug boot and messing around with that little spring and getting the alligator clip around it properly to get a good reading.