Ignition Switch Bad?

[Kargh]

Hello Again,

1977 Mercury 1500

I bought the boat home this past weekend and decided to do some work on it. When I put the key in and turned it on, I had no power to any instruments, tilt, etc. Thinking it might have been the absolute disaster of wiring at the battery, I went through and cleaned everything up, organized it, replaced any bad ends, etc. Put key in, turned it on, and no power.

I believe sometime in the past, someone replaced the original throttle shift lever and such. The ignition switch looks like:


I've noticed that when the key is off and I connect a multimeter to the red wire and ground it, I have 12+ volts. When I turn the key to on, I have 0 volts. I'm not sure if that is what is expected or if I should have voltage on another line. Is there a way to test the switch? Does anyone else have any thoughts on why I'd have no power with key on?

I'd appreciate any thoughts or suggestions so I can get this fixed and move on to something a bit more... fun.

Thanks!

 

[Chris1956]

The red wire should have voltage to it at all times. If voltage goes to zero when the key is on, either you have a bad supply of voltage to the switch (likely), or the ign accessory wire is shorted to ground. If you have a short, normally you would observe some heat, at the site of the short.

Check the red wire on the switchbox on the motor for power. Then check the quick disconnect plug for dirty or broken contacts. Obviously, the positive battery cable connects to the red wire at the motor. This is the power supply for both the ign switch and the switchbox. Check this internal connection.

You could connect a jumper wire from the +12VDC side of the starter solenoid to the red wire on the switchbox, and see if that fixes it.

 

[Kargh]

Hello Chris,

Thanks for your reply, I really appreciate it. One of the issues I'm facing is that in the past this was all rewired and whomever did it, well, it looks like they ran all their own wiring and none of the colors really make sense. In fact, it almost looks like he used whatever he had lying around. I have red wires that connect to ground, black that go to positive, some change colors several times as it looks like he was using left over pieces, etc. I'd really love to tear all the wiring out and just redo it properly, or at least in a manner that I could understand and trace.

If I'm understanding you correctly, the power from the battery actually runs to the motor first, then to the ignition key? So if there is something shorted, dirty, broke, etc between the battery -> motor -> key, then the key wouldn't work and if that doesn't work, then the accessories wouldn't get power?

Thanks for your time. I don't really have a clue how this is all connected, and as I said, it is such a mess that it is difficult to even begin to get some sort of mental picture. At least understanding HOW it should be hooked up will help in tracking what goes where.

 

[Kargh]

One more thing, and sorry if this comes across as sounding like a complete idjit. What would the expected results of connecting the jumper wire be? I'm guessing that it would eliminate the connection between the battery -> motor plug -> switchbox as being bad (assuming that the jumper wire didn't change anything)?

 

[Kargh]

Okay, I tested voltage at the switchbox and there is 12.45v w/key off and 12.35v w/key on. voltage at the ignition switch drops to 0.06 w/key on.

 

[Kargh]

So, apparently I now have power again. maybe it was just a dirty connection at the motor. I noticed one of the male ends was fairy crappy looking so I cleaned it up as much as I could.

 

[Chris1956]

Obviously the voltage to the switchbox should be steady and at least 12VDC. It sounds like you have some issues in the engine wiring harness. Since the motor cranked well, I suggested the jumper from the hot side of the solenoid, since it clearly has good voltage, to the switchbox to help make sure the ign system has good voltage. As you suspected, the battery cable runs from the battery to the starter solenoid, and there is some internal connection to the power wires on the engine.

You might spring for a new engine harness. They are a bit pricy, but avail. Check surplusunlimited's web site.