78' Merc 1150 switchbox problems

[Davem1754]

This time last year I replaced my switchbox with a used one and it got me spark back and ran fine until the 2nd time I started it this year, back to no spark. Last year I also replaced my ignition switch because on occasion, when I turned the key off, the motor stayed running. The new switch did not fix this problem and I am beginning to think I have a short somewhere. I have ordered a new switchbox but want to make sure something else is not taking them out.
I have replaced bad corroded wires on the motor itself and ohmed the wiring back to the switch but am un sure if it is an intermittent short somewhere or just another bad swichbox.
Any suggestions will be surely appeciated.

 

[verado7]

Re: 78' Merc 1150 switchbox problems

buying a used switch box is a big gamble - they are just a type of part that can fail tommorow or in ten years .

 

[Chris1956]

Re: 78' Merc 1150 switchbox problems

If that motor has a distributor, you must have +12VDC on both the red and white wires on the starboard side of the switchbox, in order to have spark. Power on the white wire comes from the ign key. I recommend you check these connections.

 

[Davem1754]

Re: 78' Merc 1150 switchbox problems

I do have 12v on red and white wire, drops to 11v on dist. side when the key is turned.
Thanks

 

[Davem1754]

Re: 78' Merc 1150 switchbox problems

I am still wondering if the issue of turning the key off and the motor staying running contributes in anyway of the switchbox failing.
This time I ordered a new switchbox but want to make sure I dont have a short between my key switch and motor.
Can anyone shed some light on this for me?
Thank you for your time.

 

[Chris1956]

Re: 78' Merc 1150 switchbox problems

Dave, When the ign is switched off, the white wire should drop to 0 volts, and the motor will stop. Since you know your ignition switch is acting up, I would suggest you repair it first, before installing another switchbox.

 

[Davem1754]

Re: 78' Merc 1150 switchbox problems

Chris, I found some more bad wires in my controller unit, hopefully I have it taken care of.
Thanks for your time and suggestions.