1977 Merc 500 -- everything's grounded out!

[fullthrottle_man]

I've been trying to get my 50hp going and have no spark. The whole system is grounded out on the motor side. I know it's not the mercury switch because if I take it off and test the resistance it's fine. As soon as I bolt it back on, it's grounded out. I checked all the wiring and all is in good condition/connected where it was last time I took it out and ran it (about 2 years ago). It cranks just fine, I just have no spark due (I think) to the system being grounded out and I have no clue as to where to go from here. The switchbox is grounded out on most of the terminals, as are the coils. Anyone have any ideas or suggestions besides investing money in a manual and waiting for weeks for it to show up?

 

[cannonford57]

Re: 1977 Merc 500 -- everything's grounded out!

if it fires w/o the mercury switch,dump it if not check the ign switch.....with age comes corrosion frayed,broken wires,also what kind of shape Are the wires in the internal harness in...if the covering on them is shot it could be there....hope it helps.

 

[fullthrottle_man]

Re: 1977 Merc 500 -- everything's grounded out!

It doesn't fire with or without the mercury switch. The ignition switch tests out good (continuity to the spots it's supposed to with the key in the corresponding position). But when I tested the motor side of the harness, the orange cutoff wire's post has continuity to all the other posts except one. The trigger tests good, the stator tests relatively good (the ohm readings were slightly higher than they were supposed to be but not by much). Would a bad rectifier cause the whole harness to be grounded? I haven't found a way to test the rectifier yet... Any ideas?....

 

[cannonford57]

Re: 1977 Merc 500 -- everything's grounded out!

there is an ohm test for the rectifier,sorry dont remember the #s....somewhere here does i'm sure....just disconnect the darn thing and see.what can it hurt?you can disconnect the harness from the control box to the engine,disconnect the black wire w/yellow tracer from the switchbox(i think,somebody back me up)with a jumpbox spin the engine if it fires the prob is up front.