2005 4.3 liter Mercruiser ignition trouble

[Pmt133]

You should have 12v at the starter. Possibly a fusable link there then that ties up to the circuit breaker as a red/purple then goes to the 10 pin. From there if it visually looks fine check the red/purple at the dash. Obviously any point you can test it, if it tests good while cranking then drops testing at the next point you've found your issue.

See posts 3 and 4 here for diagrams that will be similar. Mercruisers are all pretty standard as far as color code and wiring.

 

[nola mike]

What’s the voltage drop test that I haven’t done. Where else am I checking it? Is there something between the ignition switch and the coil? I was assuming it was the same purple wire between ignition switch and coil which was telling me the switch

Voltage drop test is measuring the voltage on either side of a connection when it's under load. With your meter on DCV, you probe each side of the connection. The voltage should be close to zero. If it's higher than that it means there's significant resistance across the connection, either because of the component (eg ignition switch), bad connections, or bad wire. You can also do it on the ground side of the circuit, and you can test larger sections/multiple connections first and narrow it down if there's a drop. Keep in mind that your voltage drop is not necessarily because of a positive connection. Aside from grounds (helm, cannon plug, main ground), positive connections that I can think of off hand:

1. Battery to starter
2. Starter to circuit breaker/across breaker
3. Breaker to cannon plug
4. Dead man switch
5. IGNITION FUSE (esp if you have the glass fuses)
6. Ignition switch

EDIT: Also, since you have an electric fuel pump, and this is during cranking, you could also potentially have problems with the yellow/red wire (if it's tripping the starter though, it would have to be either at or past the slave solenoid) or the purple/yel wire from the starter across the oil pressure switch. Note that some of these connections are more likely culprits than others...

 

[alldodge]

10 pin engine connector visually looks immaculate. Not sure how or what to check with volt meter.

Pull the connector off and look at the pins, many times the pins become corroded

Anyone have a diagram of this? I need a map

This is where it's good to know actually which 4.3 your have. Being a 2005 and you saying it's a carb than most likely has a TKS

 

[kepruno]

Pull the connector off and look at the pins, many times the pins become corroded


This is where it's good to know actually which 4.3 your have. Being a 2005 and you saying it's a carb than most likely has a TKS

I did pull the connector. There is no corrosion of any kind. It looks brand new. For some context this boat has spent most of its life in a garage that never gets below freezing in the winter. Most if not all connections have little to no corrosion. I will check all that I can find but a “bad connection” or “bad ground” is probably not my issue. Important to note that this started while the boat was running. I get that it can still be a connection issue it just seems unlikely to me given the condition of the things I have checked.

Ignition switch looked ok aside from the voltage drop and there is nothing wrong with the 10 pin visually. Any suggestions on next step? Just check as many connections as possible for corrosion and voltage drop? What’s before and after the ignition switch?

 

[Pmt133]

You could check 12v into the ignition switch since you're losing it there. If the supply side of the switch is fine your problem is the switch. If it also dips you'd have to start running down the line then back to the 10 pin and engine harness. There may also be splices up under the dash.

I suppose a bum electrical component on the circuit could also cause it but again, you need to isolate if its the feed coming in or what. Since you have the same 4v cranking at the key though, I'd start at the key supply and work my way back to the engine...

 

[alldodge]

Ignition switch looked ok aside from the voltage drop and there is nothing wrong with the 10 pin visually. Any suggestions on next step? Just check as many connections as possible for corrosion and voltage drop? What’s before and after the ignition switch?

The key switch purple wire has 12V with key ON and 4V when cranking.

The red/purple wire comes from the 50 amp breaker on the motor, to the 10 pin connector, to a 20amp fuse/breaker at the helm, to the key switch

You have a bad connection either the key switch or something else between key switch and 50amp motor breaker

 

[kepruno]

Ok. I get it now. I’m so used to black and white I think all the colors were scrambling my brain. But it’s a switch so I need to check both sides, which I have now done.
The supply on the ignition maintains 12 volts while cranking the purple wire does not.

 

[kepruno]

New switch same problem.
I have every wire disconnected except red/purple supply. Turning key to start results in zero voltage at the purple wire tab. So this either means the new switch is junk or it’s not supposed to be supplying power to that wire during cranking

 

[nola mike]

New switch same problem.
I have every wire disconnected except red/purple supply. Turning key to start results in zero voltage at the purple wire tab. So this either means the new switch is junk or it’s not supposed to be supplying power to that wire during cranking

that red/purple is always live. it isn't a problem with the switch if you're losing power at that wire when cranking.

 

[kepruno]

that red/purple is always live. it isn't a problem with the switch if you're losing power at that wire when cranking.

Please read the post again. That’s not where the power loss is.

 

[kepruno]

To clarify. The supply wire never loses power. The tab where the purple wire is supposed to be connected is what loses power when the key is turned to start

 

[nola mike]

Please read the post again. That’s not where the power loss is.

sorry, I misread it. so you do have 12v at the red/pur when cranking

 

[kepruno]

sorry, I misread it. so you do have 12v at the red/pur when cranking

Yeah. Every wire except the purple has or gets 12 volts when the key is turned to start. To further clarify, every single wire is disconnected except the power.

 

[nola mike]

Yeah. Every wire except the purple has or gets 12 volts when the key is turned to start. To further clarify, every single wire is disconnected except the power.

so test the resistance across the terminals is the ignition switch and see if you're getting continuity between b and i/s when in run/start

 

[alldodge]

To clarify. The supply wire never loses power. The tab where the purple wire is supposed to be connected is what loses power when the key is turned to start

Including when the key is turned to start?

If correct
Post a pic of the back of the key switch with wires on it

 

[kepruno]

Including when the key is turned to start?

If correct
Post a pic of the back of the key switch with wires on it

I was today years old when I learned (I) is for ignition.
Been testing the wrong lead. The A connection also has a purple wire but it’s purple/red. The (I) connection almost looks maroon but either way I’m a dumbass and back to checking connections and grounds.

 

[kepruno]

I was today years old when I learned (I)View attachment 410666 is for ignition.
Been testing the wrong lead. The A connection also has a purple wire but it’s purple/red. The (I) connection almost looks maroon but either way I’m a dumbass and back to checking connections and grounds.

You can see the purple wire I should have been checking in the back. The red wire that is coming off the same lead goes to the warning squealer.

 

[kepruno]

You can see the purple wire I should have been checking in the back. The red wire that is coming off the same lead goes to the warning squealer.

The switch must kill the accessories to save voltage while starting the engine

 

[alldodge]

Purple on I

 

[JustJason]

Get a 12-14 gauge jumper wire with alligator clips and clip one end to the same terminal on the key switch, the other end to the positive terminal on the ignition coil. Just run the wire right across the boat. Bet it starts.