Yanmar Starting Issue – Ignition Switch Problem

[Homer Shannon]

My friend Gordon recently purchased a 1988 Freedom 36. He and his wife sailed it home from Stamford CT to Newburyport MA without any significant issues. When Gordon went down to the boat on Friday, it would not start. Today, Sunday, he spent a number of hours chasing the problem. I have fairly good electrical skills and I volunteered to assist if he needed me. We worked the issue for about two hours and left the boat stumped.

After sorting out some issues with a rather cheapo multimeter and difficulties finding reliable grounds for checking voltages, we got to a point where we were getting consistent, if not understandable, results. The boat has a Yanmar diesel (I don’t know the model) and it equipped with a standard Yanmar ignition panel and wiring harness. The battery bank on the boat consists of four batteries in a house bank and single battery as a starting battery. There is a standard A/B switch for the batteries. The batteries are not in great shape. They show about 12.2v on the instrument panel, and although this is low, it does not seem low enough to totally kill the system – even with the switch in the “both” position.

The primary symptom is that the engine does nothing when the ignition switch is switched to on and the start button is depressed. Gordon said that normally the panel will buzz when the ignition is on but the engine is not running. The panel is not buzzing at all.

We traced the wires from the ignition panel back to the motor, starter, circuit breaker, A/B switch and batteries. Using the multimeter we determined that all the wiring was good and that there was 12.0v at the ignition switch. The actual key switch has two connectors on it: one with a large, about 10G, red wire, and the other with two smaller wires, perhaps 14G, one red with a black stripe and one white. The white wire goes to the starter button. With the switch in the off position there is 12.0v at the large red wire and 0.00v at the white wire. When the ignition is switched to “on”, the voltage on both connectors becomes 0.10v. Depressing the starter button does not change the voltage reading. We tested the starter switch for continuity and it is OK. Gordon had tried another ignition switch earlier in the day, so I did not get involved in replacing the switch itself, but the switch seems good. We tried moving the white wire to the lead with the large red wire, effectively hot-wiring the boat. The same situation persisted; the voltage dropped to 0.10v. No buzzer, no starter.

Finally we went and got another battery – not a very good one but it had 12.37v as tested with the multimeter. We used jumper cables to connect this to the starting battery. Again we tested the voltage at the ignition switch. This time we had 12.0v in off position but 0.008v in the on position – less than with the starting battery alone.

That is where we left it. We are stumped as to what is happening and don’t understand the 0.10V reading out of the ignition switch at all. Does anyone have any suggestions?

[Wotname]

Originally Posted by Homer Shannon

....
Using the multimeter we determined that all the wiring was good and that there was 12.0v at the ignition switch. The actual key switch has two connectors on it: one with a large, about 10G, red wire, and the other with two smaller wires, perhaps 14G, one red with a black stripe and one white. The white wire goes to the starter button. With the switch in the off position there is 12.0v at the large red wire and 0.00v at the white wire. When the ignition is switched to “on”, the voltage on both connectors becomes 0.10v. Depressing the starter button does not change the voltage reading. We tested the starter switch for continuity and it is OK. Gordon had tried another ignition switch earlier in the day, so I did not get involved in replacing the switch itself, but the switch seems good. We tried moving the white wire to the lead with the large red wire, effectively hot-wiring the boat. The same situation persisted; the voltage dropped to 0.10v. No buzzer, no starter.
...... Does anyone have any suggestions?

OK, first the short answer.
You have made an error while checking the wiring initially. The large red 10G wire and it's associated connectors / fuses etc is not good. The voltage on this wire should remain at around 12V when the switch is ON. Until this is sorted out, nothing else will work.

Longer answer coming shortly...

[Wotname]

Longer answer...

Older Yanmar panel wiring typically has a positive power wire (about 10G) red wire going to the ignition switch. It originates from the engine loom and usually has a inline fuse (often near the alternator or stater motor).

Typically the circuit is Battery +ve pole, main master switch (1/2/both ect), starter motor solenoid, alternator B+ terminal, inline fuse (say 30A), engine loom multi-pin connector, panel connector (if extension harness has been fitted) and finally the ignition switch.

Anytime the master switch is ON, there should be battery volts on the wire and it should stay roughly the same regardless of whether the ignition switch is ON or OFF.

The fact you see 12V on this wire when the switch is OFF but not when it is ON suggests there is a high resistance in the above circuit - likely to be corrosion in a multi-pin connector or in the inline fuse terminals.

This red power wire supplies the +ve feed to the buzzer, idiot lights, tacho, start switch and the starter motor solenoid. Any defect in the red power wire will stop all of these items from working.

I would recheck your trouble shooting by measuring the volts on the big wire on the starter solenoid with the ignition switch ON - should be ~12V. If so, now measure the voltage on the red wire on the ignition switch (with the switch ON) - should be the same (within say 0.5V) of the previous voltage (i.e. ~12V). If not, find out why .

As a proof, you could run a temporary jumper wire direct from the battery +ve pole to the ignition switch and I'm sure the buzzer will now work and if the start button is pressed, the engine will start.

There is another common Yanmar start circuit defect and others may post about them but at this stage, that isn't your problem right now although it maybe so in the near future

[Wotname]

A picture is worth a thousand words...

This is a typical Yanmar small engine harness - your's might be slightly different but not by much.

[wingssail]

Originally Posted by Wotname

A picture is worth a thousand words...

This is a typical Yanmar small engine harness - your's might be slightly different but not by much.

The OP owes you a consulting fee

[Wotname]

Originally Posted by wingssail

The OP owes you a consulting fee

If the advice resolves the OP's problem, I sure his mate Gordon will buy a round of drinks or a bottle of fine red next time he is down-under...

[Homer Shannon]

Wotname, it figures I could count on you for solid advice. Thank you.

We did check the voltage along the power line that you describe. The fuse is good and there is power into it and out of it. The line next goes to a connector by the transmission and it has power. We didn't disconnect the harness connector at the panel, which is another point of resistance. We should definitely look at that. Perhaps more careful testing with an ohm meter can pinpoint the problem. In any event, I think your suggestion of bypassing the whole lot with a wire from the battery directly to the ignition switch is a good one. I think bringing down a battery with a full charge would also be a good idea.

Gordon's still a working man (has to pay for his new boat, you know) but I'm sure he'll be anxious to give this a shot.

[Wotname]

^^ Thanks for the kind words Homer.

I have made the assumption (possibly false) that you have a solid 12V on the starter solenoid when the key switch is ON but if you don't, then the problem lies further back towards the battery (cabling / master switch etc).

I'm sure you have a good grasp of basic electrical troubleshooting so it's not my position to tell you how to proceed however allow me to tell you how I would do it.

I have found that measuring resistance (ohm meter) is problematical when dealing with intermittent faults - results are inconsistent and Gordon's fault is somewhat intermittent. It has been working but isn't right now.

I prefer to make voltage measurements to find where the voltage drop occurs BUT this only works if you make the measurements while the circuit is under load. Open circuit voltage measurements are nearly worthless IMO.

To reiterate, the voltage at the key switch must be close to battery volts (12V) at all times when the switch is ON.

Wish Gordon all the best in his trouble shooting!

[GordMay]

Wotname has given you very good advice.
Remember, a nominally 12V LA battery should show an open circuit (on, but no load) voltage of about 12.7+ Volts at full charge. An OCV of 12.2 is about 50% discharged.

[Sailmonkey]

Remember when troubleshooting electrical curcuits that a wire may display voltage until a load is applied. If the voltage plummets when a load is applied this indicates a high resistance connection somewhere within the circuit.

[Homer Shannon]

We're going to give this thing a go again this afternoon. We will be bringing a fully charged battery and a length of 10G wire sufficient to bypass the whole run.

My one question is this: At one point we disconnected the buzzer lead and moved the white starter lead from it post and put it directly on the hot post of the starter switch. I'm pretty sure we were then seeing the 0.010v. The button was not being depressed, so what was the load that was causing the voltage reading to drop from 12.0 to 0.10?

Perhaps we ran the test wrong - we can look at it again. At least now we are armed with some good knowledge and a schematic of the wiring.

[Captain Bill]

I agree that the problem is likely a high resistance problem from the battery to the switch, but don't discount the possibility that the problem is in the battery. I once had a cracked battery post that acted just like the OPs description. I spent hours trying to find the problem in the wires. I finally found it by checking the voltage directly on the battery posts when a load was applied.

[keepondancin]

I think most of us who do their own repairs have been through this. As others are saying, you have weak batteries, even the extra one you brought.. that and probably some less than good connections, caused by being loose or corroded, and you are not getting full power to the system. Happens to all of us. Chased a similar situation on a tractor, and it was just corrosion at a fuse. You will find it.

[Wotname]

Originally Posted by Homer Shannon

We're going to give this thing a go again this afternoon. We will be bringing a fully charged battery and a length of 10G wire sufficient to bypass the whole run.

My one question is this: At one point we disconnected the buzzer lead and moved the white starter lead from it post and put it directly on the hot post of the starter switch. I'm pretty sure we were then seeing the 0.010v. The button was not being depressed, so what was the load that was causing the voltage reading to drop from 12.0 to 0.10?

Perhaps we ran the test wrong - we can look at it again. At least now we are armed with some good knowledge and a schematic of the wiring.

Very good question and not being there, I can only speculate.

There might be other circuits that a previous oner has added to the ignition circuit somewhere or perhaps there are other faults like a partial short to ground (i.e. battery -ve).

[Wotname]

One thing I have found over the years is that Ohm's law is never wrong. If something doesn't appear to make sense, it is always me that is lacking understanding of the circuit (or of the fault), it's never Ohm's law changing changing it's mind.