Gregory Bender

Ignition coil operation test

Moto Guzzi V700, V7 Special, Ambassador, 850 GT, 850 GT California, Eldorado, and 850 California Police models



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Thanks to Joe Jump who posted this information on the Yahoo! Loopframe_Guzzi news group in reply to a post from Jon (lennonjas). In Joe's own words:

Since it is so uncommon for an ignition coil to go bad, I'd recommend one last check to absolutely verify you have a bad coil. I'd recommend you isolate it down to ONLY the coil being tested. You could do this by...

  1. Disconnecting the low tension wires of the bike's harness from your coil - the switched hot lead from the ignition switch, the neg lead that goes to the dist, and the lead to the tach (if so equipped), and anything else that might be hooked up to the coil.
  2. Remove the high tension lead running from the from coil to dist and replace with one of the spark plug wires with a known functioning plug (lawnmower, good used plug, etc.). Lay the spark plug on the engine case somewhere so it gets a good ground.
  3. Connect one end of a scrap piece of primary wire (aprox. 16 gage, most anything will do) to the negative side of the coil. Strip the other end & twist the strands - you will be momentarily touching this end of the wire to a chassis ground. A test lead equipped with a couple alligator clips would be ideal.
  4. Connect another test lead from the battery pos post to the positive side of the coil. Once again, a test lead with alligator clips would be great.
  5. Momentarily touch the negative test lead to ground, then remove from the ground while watching the spark plug, looking for a spark. The coil should spark once every time the lead is lifted off the ground.

This set-up should eliminate all other variables & isolate your troubleshooting down to the coil. You won't be distracted by cranking the engine over or worrying about getting zapped - you can concentrate on watching the plug looking for a spark. If this test results in a spark at the plug, your problem is not in the coil. At that point I probably would reconnect the pos lead from the harness to the coil & try again. If good, add more components one at a time until you isolate where the problem is.