Re: Merc 115 1974 serial 3272927(no spark!!!)
Stan,<br /><br />Now we have to test a few things. First of all we'll disconnect the 'mercury switch'. No, this isn't a switch developed by Mercury. It has mercury inside it and when the engine is tilted up too far it'll shutdown the ignition system. So, disconnect it and check for spark. Oh, forgot to tell you where it lives, sorry. You'll probably find it bolted to the side of the engine block somewhere (my memory is a bit dim at times, been a few years since I spannered one of these engines),
but, it does have a wire running to the switch box, brown one. So, go to the left hand side of the switch box and you'll see 3 terminals, black, white and brown. The brown should have 2 wires on it. One goes to the dissy (with the black and the white) and the other goes to the mercury switch. Remove this wire and check for spark. No spark? Now we move to test the switch box. Now listen carefully 'cause it's easy to get this bit wrong, and I don't want you asking me to explain it again.
<br /><br />With a multimeter perform the following checks.<br />1. Connect the red lead (of the multimeter (MM)) to the white terminal on the 4 terminal side of the switchbox, and the black lead of the MM to engine ground. <br />2. Turn the igition key 'ON" and you should see 12 volts. If not, key is faulty.<br />3. Move red lead of MM to the brown terminal (still with the mercury switch disconnected) on the 3 terminal side of the switchbox. With the Key 'ON' you should read 12 volts again. If not, the switchbox is faulty.<br /><br />The rest of the tests require a thing called a "Direct Voltage Adapter", which I doubt you have.<br /><br />You could try a resistance check on the ignition coil. Remove the green wire from the switchbox and measure the resistance of the coil primary to ground. It should read just a few ohms. The secondary side of the coil can vary from a few hundred ohms to a few thousand. If you have a complete open circuit that could also be your problem. <br /><br />Best I can do 'over the phone' Stan.<br /><br />Chris.............
