Merc Starting Trouble??

[southernpride72]

I have a 1978 mercury 500 (50hp) that is haveing starting trouble. I have narrowed it down to the rectifyer ground wire. All of the insulation is burnt off. When I try to crank it, the moter BARLEY spins, and the wire gets really hot. I tested the wire to see if it was getting voltage during cranking, and it is receiving 10v. Not Good! Why is the groung getting power? I have tested the rectifyer, and it is good. ANY help would be GREATLY appreciated!

 

[southernpride72]

Re: Merc Starting Trouble??

I just hand-cranked the engine to check a few things...i checked the voltage of the rectifyer ground wire (against the main ground)while it was running and it showed 170v (yes 170!!). i checked the battery as it was running, and it is overcharging at 22-27v. Hope this info helps. Thanks!!!

 

[southernpride72]

Re: Merc Starting Trouble??

anyone?

 

[ricksrster]

Re: Merc Starting Trouble??

It looks like you have a serious wiring problem. Check all yours wiring for broken, cracked, loose wires and dirty connections. you can repair or buy a new internal harness. The voltage numbers you have look like HS and LS stator coil's peak voltages. A manual will help you sort everything out.

 

[southernpride72]

Re: Merc Starting Trouble??

So am I getting kickback voltage through this ground wire from the stator?

 

[ricksrster]

Re: Merc Starting Trouble??

Check your wiring and see if anything is grounding out.

 

[ricksrster]

Re: Merc Starting Trouble??

What wires did you get the 170v and 22 - 27v from?

 

[southernpride72]

Re: Merc Starting Trouble??

170v when checking the rectifyer ground wire against the main ground, and 22-27v at the battery (both taken) while the engine is running.

 

[ricksrster]

Re: Merc Starting Trouble??

Disconnect the blue and the blue/white at the switch box.<br />1) connect a multimeter to these wires and check resistance. You should show 5800 - 7000 Ohms. <br />2) check resistance between blue and ground. Should have no continuity.<br />3) Now disconnect the red and red/white wires from switchbox. Check resistance between the two wires. It should be 30 - 90 Ohms.<br />4) Check between red and ground. Should have no continuity.<br />5) Disconnect yellow wires at rectifier. check resistance between these two wires. You should have about .75 Ohms.