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Please Help 1978 500 50 hp thunderbolt won't start

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Proudpotter

New member
My 1978 500 50 hp has ran great for the last two years I adjusted the throttle cable a little the other day and it started fine. The following day I went to the lake and nothing. Like it has no spark at all. I noticed the ground on the mercury switch had corroded off so I bypassed it and just grounded to the case. Still nothing. Anyone have any suggestions. By the way it is a 4 cylinder with thunderbolt ignition. Thanks in advance for any help out there.
 
..." I noticed the ground on the mercury switch had corroded off so I bypassed it and just grounded to the case."

Ah hah! You sabotaged yourself! Remove that wire and don't bother replacing the switch--it's worthless.

Jeff

PS: Thanks for a good laugh.
 
Well I removed the wire and still won't start seems like there is no spark plenty of fuel and good compression.
fastjeff said:
..." I noticed the ground on the mercury switch had corroded off so I bypassed it and just grounded to the case."

Ah hah! You sabotaged yourself! Remove that wire and don't bother replacing the switch--it's worthless.

Jeff

PS: Thanks for a good laugh.
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Yes... try disconnecting the orange wire at the switch box then see if you have fire to the spark plugs. The orange wire paths that particular post on the switch box to ground when the ignition switch in the off position and is "open" from ground when the ignition switch is in the on position.

kimcrwbr1 - what would be the cause or source of the tar / goo are you mentioned? ...shorted wiring?
 
The reason I asked about the goo... I just recently acquired a 1978 model 500. It was missing on the #2 cylinder so after doing some troubleshooting (using the CDI documentation) i replaced the switch box and now it is running great. Although the continuity checks I did indicated the trigger assembly and stator to be okay, I do see where some goo has seeped down from the stator where the wiring harness comes out of it. That said, I probably need to go ahead and replace the stator too or else it's highly possible the new switch box will become toast like the old one did.
 
I feel like I have made some progress I removed the orange wire and it fired right away. What should I do next? Search for a short in that orange wire? Thanks so much for all your help I am really new to outboard motors and you guys have been amazing.

kimcrwbr1 said:
http://maxrules.com/oldmercs/Wiring/1966ona/500_76_78eL.jpg
With a volt meter check for power at the orange wire at the switchbox key off and key on if it has power the switchbox is probably fried. Disconnect the orange wire at the switchbox and see if you get spark if it starts the ignitin switch is bad or there is a short in the kill wire to ground. Otherwise you will need a DVA adaptor to troubleshoot the ignition. Go through the wiring complete clean all connections and sand all grounds metal to metal. Look under the flywheel and see if there is any tar like goo dripping down. It takes a special puller for the flywheel do not try and use a jaw type puller you will need a new flywheel. Disconnect the battery and go through the wiring then get back with us. Oh yea have you checked the compression?
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Tested the orange wire at the switch and no voltage reading at all. So i assume it's a bad wire or a bad ignition switch. Is that correct?

Proudpotter said:
I feel like I have made some progress I removed the orange wire and it fired right away. What should I do next? Search for a short in that orange wire? Thanks so much for all your help I am really new to outboard motors and you guys have been amazing.
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Well I found some really bad wires and repaired them she fired right up and purrs like a kitten without the orange wire and as soon as I touch it to the terminal it kills it. Anyone have any ideas?
 
Got it!!!! Orange wire was off the ignition switch soldered it back on everything works great. Thanks again for all the help. And at least I got some old corroded wires fixed in the process.
Proudpotter said:
I understand that but with the key in the run position it should not kill it correct?
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