1970 mercury 500 thunderbolt wiring ?

motor has not ran for 2 years. should there be 12 volts going to the distributor? or the switchbox?<br />I don't have voltage in either place. is the mercury tilt switch normally open? or normally closed? plugs are ngk BUHW have never seen plugs like these before are these the correct ones for my motor? I have 4 wires coming into the motor as follows.<br /><br />grey- electric choke (works)<br />red- connects to small box conected to flywheel stator leads (has voltage with key on or off)<br />yellowish- goes to switchbox (no voltage)<br />orangeish- goes to switchbox (no voltage)<br /><br />the red wire doesn't go anywhere else how does the distibutor get voltage?<br /><br />motor has no spark<br /> <br />I would greatly appreciate any advice from an old merc expert!<br /><br />billy sea

Re: 1970 mercury 500 thunderbolt wiring ?

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Re: 1970 mercury 500 thunderbolt wiring ?

Not real sure on those Mercs, but here's some good diagrams that may get you started until the Merc guys get on here. I believe the Mercury switch should be open when down and in the tilted position it grounds the ignition. BUHW is the correct plug. It is a "Surface Gap" plug.<br /><br /> web page

Re: 1970 mercury 500 thunderbolt wiring ?

Billysea, On my 72 thunderbolt Mercury (80hp) there are three wires on the distrbutor which I believe go: black=ground, white=12 volts and blue is the trigger voltage for the "Box" My trim tilt-switch shorts out upon tilting UP and that shorts the output for the distributor so that the spark stops completely. To test the tilt switch, just remove the wire from the ignition box where it parallels the blue wire from the distibutor. Hope this helps... Jim Reed

Re: 1970 mercury 500 thunderbolt wiring ?

Hey thanks Jim got the diagram and that helps. I just have one question does the salmon wire that goes to the blue connection on the switchbox carry voltage? if not how does the distributor get the 12 volts it needs to fire the plugs?<br /><br />billysea

Re: 1970 mercury 500 thunderbolt wiring ?

I really need to thank rick for the wiring diagram<br />so thanks rick I greatly appreciate your help. I am just trying to figure out how voltage gets to the plugs. Is there a magneto in the distributor?<br />Does the stator provide the fire , or is that just a charging system. <br /><br />this is a great forum<br />billysea

Re: 1970 mercury 500 thunderbolt wiring ?

There are two ignitions listed for the 1970. Does your switchbox have red, blue, white & green terminals (and that's it)? If so, is the orange wire (salmon?) from the remote control connected to the blue terminal on the switchbox, just as the brown wire from the tilt switch is? If so, the orange wire is just a ground - that is, kills the ignition by grounding it, just as the tilt switch does. <br /><br />Be careful - if it does start now, you have no way of stopping it (choke it, or be ready to ground that blue terminal again). If you've got the switchbox described above, your ignition is self-energizing & doesn't need a battery to run. <br /><br />The 'self-energizing' part all takes place within the distributor-looking thing, which merc calls the ignition driver. Merc doesn't call this a magneto, though it clearly has magnets swinging around inside the "ignition driver". (They do call the earlier ignition "magneto".) No points. There's 8 poles inside the driver & two coils. If you've got a scope, the voltage between either red or white, relative to blue, is sawtooth, 4 cycles per engine revolution. A capacitor (inside the "switchbox") charges on each upswing (tooth), and an SCR goes conductive each downswing, sending juice (140V) to the coil. The coil output really packs a punch on these, so watch it if you're messing around with it.

Re: 1970 mercury 500 thunderbolt wiring ?

I mean if you disconnect the orange wire, you'll have no way of stopping the motor.

Re: 1970 mercury 500 thunderbolt wiring ?

Hello and a big thanks to ledgefinder I am really getting somewhere now. I have been trying to start my motor with a battery off a 25 h.p. tracker, is the battery too small? The motor is turning over kinda slow I even tried jumping it off my truck. Do I need a bigger battery?<br /> thanks again ledgefinder<br /><br />billysea

Re: 1970 mercury 500 thunderbolt wiring ?

I'd just rope start it.

Re: 1970 mercury 500 thunderbolt wiring ?

I have a question for you about a motor I have. I think I have the same distributor (if you have the switchbox with the red, blue, white & green terminals). When you turn the pulley on the distributor, does it move smoothly or sort of snap-though? I can turn mine a little due to slack in the drivebelt, and it snaps through to another position so that the drivebelt is now tight on the other side. I can't tell if it just some magnets lining up inside the distributor, or whether I've got a bearing problem. <br /><br />I've had two other of these motors (a 71 and another 74) and never noticed this behavior. The thing ran fine for a week of vacation last summer - whatever it is doesn't seem to be getting any worse. I'm probably going to sell it & don't want to pass on something that'll just bust on the next guy. Thanks!