Expert: Jeff Grigg - 1/23/2008

Question
QUESTION: Hi Jeff this switch is a mercury magneto style.I have a manual and have checked the wiring diagram all wires are in correct places,this problem existed before i started working on it.This is also my first time on this site any other suggestions,thank you.

ANSWER: John, check the voltage going to the switchbox from the wiring harness, the red and white wires. You need at least 10VDC while cranking, 12+ volts with the key on. Any less and the engine will not start. Then check the voltage on the other side of the switchbox with the key in the cranking position, you should have 9V. in the wire going to the trigger in the distributor, brown.
If you have voltage then the trigger is probably bad. I do not recommend you trying to replace the trigger yourself. Find someone that is an expert in your area on the old Mercs. They may be hard to find. Someone with very little knowledge, no matter how good a mechanic will probably screw up the distributor.
This is one of the very rare instances where I offer my services in rebuilding distributors since I am an expert on the inline Mercury's.
Do the voltage tests and post back what you find. If you need my services post back with a private posting and your e-mail address.
Jeff

---------- FOLLOW-UP ----------

QUESTION: Hi Jeff i have 10 vdc while cranking on red and just shy on white.12v with key on and just 4.98vdc on other side of switchbox ( brown wire) Thanks.

Answer
More than likely your switchbox is bad. You should have 9vdc. If the voltage is not making it through the switchbox then it can't properly fire the trigger. Keep in mind this system is a battery operated ignition system unlike the later alternator driven ignition, ADI, systems, so proper voltage is critical.
Jeff