Re: 1977 150hp merc, only has spark to plugs when starter is enguaged
NOTICE: The trigger cannot be bench tested except with the CDI Electronics Trigger Tester P/N: 511-9710 (the tester can
also be used to test the trigger while on the engine). Be sure to follow the instructions at the bottom when lining up the
rotor and disk.
Dead or no spark until you let off of the key switch:
1. Clean ALL engine ground wires from the battery thru the engine cowling, splash pan, top cowl and support brackets.
2. Verify that there is at least 9-1/2 volts on the White wire going to the switch box (from the engine harness) while
cranking the engine.
3. Verify that there is at least 9 volts on the Brown wire going to the trigger while cranking the engine. If the voltage is
low and the voltage on the White wire from the harness is above 9-1/2 volts, disconnect the wires from the switchbox,
then check the resistance from the White terminal beside the Red terminal (from the White/Red wire on the CDI
Electronics switchbox) to the Brown terminal going to the trigger. You should read 60-76 ohms. A high reading
indicates a possible bad switchbox.
4. Check resistance between the White wire and engine ground. It should read less than 1 ohm. If it reads higher, make
sure the Black ground wire is connected to engine ground.
5. Connect a secondary ground wire (12 gauge) from the negative battery cable to the base (or case) of the switch box.
6. Using the 511-9710 Trigger Tester, check the output of the trigger according to the directions for the tester.
Only has spark as long as the starter is engaged: Usually indicates a bad trigger. Test per above.
