Rectifier connections on 115 V4

[AK115V4-93]

In regards to installing a rectifier on a 1993 115HP V4 115BET, does it matter which way the green wires go? The rectifier has terminals as follows when viewing from its installed position:

B (Black) G (Green1)
R (Red) GG (Green 2)

Here is an image of a unit like mine: Link
The rectifier part number is: 6G5-81960-A0

Who knows if the previous owner messed with the connections before I purchased the engine. I just want to ensure I connect it correctly as I understand you can easily damage the rectifier if wrong. My service manual doesn’t give any useful information regarding its connections.

The reason why I am changing my rectifier is my brand new tacho bounces randomly when the engine is running anywhere from 1000 to 6000 RPM while settling every so often. Also testing with 2 other gauges shows no tacho response at all.

I was told my rectifier is on the way out by my Yamaha dealership and I need to replace it. Voltage also seems higher than usual (15.5 volts).

[boscoe99]

It does not matter which way the green wires go.

For point of reference, I am seeing one green wire from the lighting coil and one green/white wire from the lighting coil. But again, it does not matter which connects to which of the two input posts. Lighting coil is outputting AC voltage.

By the way, does one of the green wires from your lighting coil have a female bullet connector included with it?

[AK115V4-93]

Good to know. Thanks.

I will have to check on the wires, I am working off memory at the moment. If I recall correctly, I believe there is 1 black wire, 2 red and 3 green connected.

From memory I believe there are no bullet connectors near the rectifier, just ring terminals which connect to the rectifier posts. I will verify. Is this where I should be looking?

I assume the tach lead is connected here (i.e, is one of the green wires leading away from the rectifier) which is sent down the loom to the 703 remote. Thus can I correctly conclude you can hook the tacho signal wire straight to one of the green terminals on the rectifier in order to test if the 703 loom is ok? I did test with a multimeter on AC at the 703 remote control box green tacho wire end and was seeing 2.3VAC which increased as RPM increased. Only 1 of the 3 tachs I tried responded with an erratic movement.

I'm concluding that either the signal is out of spec or is weak hence pointing the blame at the rectifier. Engine starts and runs fine.

[boscoe99]

You can blame excess or low voltage on the R/R but it can't be blamed for the tachometer signal.

Tacho signal comes from the lighting coil in your model I believe.

[rodbolt17]

a quick way to tell?
look at the size of the green wires.
if you have two large about 10ga and one small about 16ga the lighting coil provides the tach signal.
with a NON US market motor that is about all I can say.

[AK115V4-93]

Appreciate the advice. Thanks.

Any ideas if not the regulator/rectifier what could be causing the erratic tach?

• The battery charges (at a bit high voltage ~15v at battery terminals - Note: Yamaha told me today this is simply too high thus regulator/rectifier not working correctly)
• All grounds and connections are good
• I have tested with a known good tach (no response) in addition to a new dash tach (jumps but shows correct looking RPM at different engine speeds)
• Tachs have been connected to a separate battery for ease of testing
• Engine runs well in the lake

Rodbolt, I will check the wire sizes.

[boscoe99]

On that model of that vintage I don't think Yamaha US would say the voltage is too high. Are any devices shutting down or flashing a caution due to excessive voltage?

If a new RR does the same you can apply an electrical load which should bring the voltage down a tad.

Given the miniscule output of current from your model a battery should not suffer any harm. Particularly if a group 24 or larger lead acid type.

[AK115V4-93]

I have no devices besides gauges and a fuel pump on the boat. A depth sounder is on the cards in the future. So nothing is shutting down due to voltage as they are just gauges.

From further discussions with outboard mechanics and Yamaha in my area today, all agree that erratic tach stems from a dying R/R unit as "it provides a reference ground to the tach" or a bad tach itself. I was also informed not to continue running the motor until the R/R is replaced as it could catch fire!

As I mentioned I see 2.3 Volts AC at idle on the tach wire. I was also told this should be at least 5 volts minimum. I can’t find any figures published in my OEM service manual for this output.

Rodbolt, I have attached a couple of photos of my R/R. It appears all the green wires are of similar size, no larger/smaller wires. Also there are no bullet connectors, just rings as per the photos.

From looking at the wiring diagrams, it appears the downward facing green wire exiting the R/R in the bottom right corner is the tach signal wire to the 703 remote. Does this sound correct?

This motor I believe is known as C115TR in the US.

[99yam40]

there is a difference in the green wire sizes, 2 are larger than the 3rd

[AK115V4-93]

Yeah in the picture it does look like 2 larger and 1 smaller, I agree. Looking at it in person it is very hard to see a difference between all 3 and all look the same size. It was kinda dark so probably didn't help me there!

In either case from my understanding it appears tach signal is sent from the lighting coil to the R/R, then possibly the R/R provides a half-wave tap signal via the bottom right G G terminal to the 703 remote for tach connection.

From my tracings it appears either:
1. Lighting coil is going bad (unlikely as battery is charging well - Yamaha says too well!)
2. Damaged wiring/connectors (all look fine and well)
3. Faulty/out of spec R/R (thinking this is the issue)

[99yam40]

Tach should be reading pulses from Lighting coil. could be bad connection on or to lighting coil or coil failing

[AK115V4-93]

Tach should be reading pulses from Lighting coil. could be bad connection on or to lighting coil or coil failing

Well that sounds like fun. That's a whole new stator isn't it?

The battery charges just fine. Wouldn't a failing lighting coil have issues charging the battery? Guess I should test the two green leads with a ohmmeter to see if it is in spec.

Ive ordered a rectifier based on what the Yamaha dealer mechanic suggested. I guess we will see if that solves the issue. By the way, the testing procedure outlined in my service manual for the R/R fails the continuity test. Might be a sign.

[AK115V4-93]

Update:

I discovered that my regulator rectifier was faulty.

How did I find this out?

• I had issues with my tachometer – One would bounce, another would show no reading.
• My voltage was high. Before I was getting 14 volts at idle, and 15 volts at 2000RPM.

After I replaced the regulator rectifier:

• Tachometer works correctly
• Voltage sits at 13.8 volts, maxing out at about 14 volts after many hours on the water with a fully charged battery.
• Lighting coil tested in spec based on Yamaha Service Manual

Problem solved!