1980 OMC 140hp electrical

[Troubled1]

I’ve been slowly getting my 1980 Starcraft 18’ in working order. Figured out the tilt/ trim issues but now I’m having ignition issues. The engine fire while cranking but won’t keep running. If I run a jumper wire from bat.+ to the + coil terminal it fires right up. I also noticed while doing this that the oil pressure buzzer would not work until the jumper wire was attached. I know I should be getting 8-10v at the coil with the key on.
From what I understand, OMC used a resistor wire in the ignition circuit. Does anyone know where I should start looking for it? I don’t want to run it with a jumper for any length of time as I don’t want to damage the new points. There is a separate solenoid mounted close to the starter, is this part of the start/run circuit? I’ve been trying to find wiring diagrams for OMC and Starcraft but haven’t had any luck.

 

[Scott Danforth]

Resistor wire should be the section of wire between the coil and choke

 

[Troubled1]

Resistor wire should be the section of wire between the coil and choke

I don’t have electric choke. From what I have found searching around, the resistor wire is fed from 12v switched power off the alternator and then spliced to the resistor wire. Would it be possible just to bypass the resistor wire and run a 1.5 ohm ballast resistor?

 

[Redrig]

Would it be possible just to bypass the resistor wire and run a 1.5 ohm ballast resistor?

I would imagine so. That's how my Ford 302 is set up.

Full battery voltage to the points while cranking.
Then with key in "run" position it is fed through a ballast resistor.

 

[RocketFox650]

I don’t have electric choke. From what I have found searching around, the resistor wire is fed from 12v switched power off the alternator and then spliced to the resistor wire. Would it be possible just to bypass the resistor wire and run a 1.5 ohm ballast resistor?

I'll chime in with a possible yes- you can't just through whatever resistor in there which I'm sure you're aware, but if the resistor wire is only supposed to be 1.5ohms, then yes, that would work. In your case, I'm curious because your voltage change is supposedly 10-25% less than your supply voltage, which is a pretty steep change that 1.5ohms probably won't achieve. Do you know any of the basic laws of electricity? Ohms/Watts Law? Not being condensing, seriously, do you know the formula? Because if you know what you're supposed to get for voltage, the amperage of the circuit, you can determine the power of the circuit and the resistance needed to make that change with a few seconds on a calculator, and if you still don't want to bother with it, LITERALLY just reply how many ohms you need, and I'll give you the color code for your resistor or the how to read what each band means, and you can make this as challenging as possible.

Idk the wiring off hand, I'd have to see at least a picture of this other solenoid to give a useful answer there mate, sorry. That could easily go either way.

 

[Scott Danforth]

I'll chime in with a possible yes- you can't just through whatever resistor in there which I'm sure you're aware, but if the resistor wire is only supposed to be 1.5ohms, then yes, that would work. In your case, I'm curious because your voltage change is supposedly 10-25% less than your supply voltage, which is a pretty steep change that 1.5ohms probably won't achieve. Do you know any of the basic laws of electricity? Ohms/Watts Law? Not being condensing, seriously, do you know the formula? Because if you know what you're supposed to get for voltage, the amperage of the circuit, you can determine the power of the circuit and the resistance needed to make that change with a few seconds on a calculator, and if you still don't want to bother with it, LITERALLY just reply how many ohms you need, and I'll give you the color code for your resistor or the how to read what each band means, and you can make this as challenging as possible.

Idk the wiring off hand, I'd have to see at least a picture of this other solenoid to give a useful answer there mate, sorry. That could easily go either way.

you obviously do not understand points type ignition systems

standard resistors do not work for ignition systems. no color coding as found on 1/4 watt and 1/2 watt resistors will help you here. you need an ignition ballast resistor which is ~ 1.5 ohms (and about 200 watts), or you need about a foot of 14 gauge ballast resistor wire.

and yes, the 1.5 ohms will give you about 9-10 volts to the coil when running which is what you need to not burn up the points.

 

[Troubled1]

getting away from the resistor wire for a bit. I put my volt meter between battery neg and the terminal on the alternator that feeds the voltage regulator. Key off, no power. Should it have power to the regulator with the key on? Either way I have none. I then pulled the pos terminal off the coil and measured the resistance (battery disconnected) from the yellow wire on the back of the alternator to the end of the wire I removed from the coil. The reading I got was 100 ohms. Should I have disconnected the connectors to the front of the boat when measuring? Should I have removed the yellow wire from the alternator? Could I test the resistor wire by running a jumper lead from battery pos to the yellow terminal on the alternator and then take a voltage reading at the pos terminal on the coil?

 

[MUNDA]

I just went though this - I wired my own external resistor. Find the ignition wire coming from the back of the ignition switch, spice a wire into the ignition wire. Grab another length of wire and run it to the positive side of the coil - make sure that you remove the existing faulty resistor wire from the circuit.

Also make sure that you have a wire coming off of the starter solenoid to the positive terminal of the coil as well. This wire provides 12 volts to the coil during cranking.

 

[Troubled1]

I’m not sure if the resistor wire is bad. I do not have power coming from the alternator to the regulator. Does the engine need to be running to have power where the yellow wire attaches to the alternator?

 

[Troubled1]

Ok. After looking closely at the wiring diagram, I realize the power comes from the ignition switch to power up the field and the coil. I had power coming into the switch but nothing at the coil. I put a jumper wire between battery pos on the switch and the run terminal. My meter was attached to coil pos and ground. I got power to the coil. New ignition switch has been ordered.

 

[Scott Danforth]

Test before you buy

Have you checked the MOB switch? Have you checked the wiring connections?

 

[Troubled1]

Test before you buy

Have you checked the MOB switch? Have you checked the wiring connections?

I tested the ignition switch. Gives power to the starter but nothing when in the run position. Jumping between power and run on the switch gives power to the coil.