Using automotive coil in 3.0L marine motor

[EcToCrUsHeR]

I was looking online on autozone and found that the coil from a chevy 5.7L (1993-1997) has the same housing and appears to be the same as the 18-5443 coil in my 3.0L mercruiser motor. The part number for the coil is C846. Any suggestions on fitment?

 

[NetDoc]

Re: Using automotive coil in 3.0L marine motor

A coil is a coil. Most any that will fit will work. That's a pretty common GM HEI coil and if the electrical plugs match, you will do fine.

 

[achris]

Re: Using automotive coil in 3.0L marine motor

A coil is a coil. ....

Not quite true. Some coils run on 12v, some on 7v. The ones that run on 7v have a ballast resistor in the circuit. Unless it's written on the outside there is no way to tell the two coils apart!

What is the ignition system on the Mercruiser? Points, EST or DDIS?

 

[EcToCrUsHeR]

Re: Using automotive coil in 3.0L marine motor

looking at the wire diagram, my ignition system appears to be the EST. I know the coil is a 12V, now the last question i have is about the resistor that's tha's supposed to be on the purple wire by the alternator. What are the specs supposed to be on that resistor, seeing my last one was in bad shape and i have to replace it.

 

[thumpar]

Re: Using automotive coil in 3.0L marine motor

The wire is the resistor.

 

[EcToCrUsHeR]

1999 Mercruiser 3.0 alternator purple wire voltage

1999 Mercruiser 3.0 alternator purple wire voltage

After searching and not being able to find a solid answer i figured put this out there. First my coil is not putting out a spark even after i replaced it so i checked the purple wire on the plug and with the ignition switch on it gets only 1.9mV. The ignition switch and battery both get around 12.5V, but if i check where the purple wire connects to the alternator i get only 1.9mV (same purple wire that goes to the coil). The large orange wire and the red wire on the alternator all get 12.5V and the ground wire checks out so i'm thinking maybe the part of the alt that the purp wire connects to is bad. BTW the boat is a 1999 Bayliner 1950, 3.0L Mercruiser with EST ignition system.

 

[EcToCrUsHeR]

Re: Using automotive coil in 3.0L marine motor

The wire is the resistor.

And at what voltage will this resistor wire have to be? I've read 7V, 8V, and 9V...not sure which to believe. I'm going to head to West Marine to pick one up, just need to know specs.

 

[EcToCrUsHeR]

Re: Using automotive coil in 3.0L marine motor

I also wanted to add that i installed the new coil and still the same issue so i started testing the wires. I'm getting 12.5V everywhere except the purple wire connected to the coil where i'm only getting 1.9mV. I traced the purple wire back to the alternator where i also only get 1.9mV at the alt. lead.

 

[Bondo]

Re: 1999 Mercruiser 3.0 alternator purple wire voltage

Re: 1999 Mercruiser 3.0 alternator purple wire voltage

Ayuh,... The purple wires are the ignition power from the keyswitch...

 

[EcToCrUsHeR]

Re: 1999 Mercruiser 3.0 alternator purple wire voltage

Re: 1999 Mercruiser 3.0 alternator purple wire voltage

Ayuh,... The purple wires are the ignition power from the keyswitch...

Yeah, I tested where the purple wire meets the ignition switch under the dash and it's getting 12.5V there. Where i'm talking about is the back of the alternator where there are 4 wires (orange, red, black, and purple) The ground is good, the orange reads 12.5V, and the red reads 12.5V, but the purple only reads 1.9mV. The purple end that goes to the shift switch also gets 2.0mV. To add to all that, i only get them reading of 1.9-2.0mV when i ground the other end of the multimeter to the battery. when i use the engine ground stud i get nothing. I know the engine ground stud is good though because i get power when using it for other componenents like the starter, and orange alternator lead.

Just checked everything again... everything on the back of the alternator gets power except for the purple plug. Can i just connect the purple where the red power is?

 

[Don S]

Re: 1999 Mercruiser 3.0 alternator purple wire voltage

Re: 1999 Mercruiser 3.0 alternator purple wire voltage

When was the last time new points and condenser were installed. They are just maintenance items on boats, and 99% of the time a no spark condition is caused by bad points.
Thousands of perfectly good coils get changed yearly due to bad points.

 

[achris]

Re: 1999 Mercruiser 3.0 alternator purple wire voltage

Re: 1999 Mercruiser 3.0 alternator purple wire voltage

The purple wire will only have 12v when the key is ON. If the key is ON and you still have no power check the fuse behind the dash, in the keyswitch wires. If the ignition system is EST you will not have a resistance wire. But if you are using a 'standard' tower type coil it sounds more like a Kettering system (points and condenser).