Wiring kit cost for A4

[alcodiesel]

The cockpit gauges wiring might be able to be prettier but what a difference! Color coded. Easy to trace.
The engine wiring came out well. The harness comes out just below the blower. The oil pressure, temperature, low oil P alarm all run along the port side. The big wires all run along the stbd side. All purple or ignition wires go directly to the coil, etc.

Hung the broom from the yard arm: Clean sweep! everything worked,100%. No arcing or sparking or insulation melting. The god of electrons smiled down on me.

I get about 3/4 of a volt more charging to the batts. which was why I started the whole adventure by removing the ammeter from the circuit and went with a V meter.

I feel this is much more reliable than the 45 year old wiring- even though the old wiring caused me very little trouble- Preventive maintenance. Very important to me as my two goals are safety and reliability.

[edwardc]

Three quarters of a volt is a huge difference! Congrats!

[ndutton]

With your improved wiring and reduced voltage drop the question now emerges, do you have electronic ignition? If yes, it's time to redo your coil input voltage→coil internal resistance→ignition system current calculation to make certain you're below 4 amps current. In my experience, 3.3~3.5 amps is the sweet spot.

https://www.moyermarineforum.com/forums/showpost.php?p=44875&postcount=1

[alcodiesel]

Thank you. Yes to electronic ignition.

Neil, you won't come up with something else once I get the amps figured out will you?

[sastanley]

Neil's question is the exact problem that arose when I re-wired my engine several years ago. I did the exact same process you did...Ammeter delete & re-wire..next thing started blowing coils.
Just need to do a little calculation and maybe a little extra resistance.

[ronstory]

Great job and looks great. Regarding the coil, the one MMI sells has the correct resistance (~4.25 ohms) and no extra resistor to deal with.

Yes, they do cost a bit more than the everyday Napa UC14SB, but are great quality and will last a lifetime... unless, of course, you leave your ignition on with the motor off for extended times. ;^)

[ndutton]

Neil, you won't come up with something else once I get the amps figured out will you?

It must seem like I derive a perverse pleasure dropping little bombs into folks' projects but when something triggers a memory I figure it's better to raise the issue now rather than read about an overheated coil and engine shut down later. As I read your rewiring success, Shawn's experience came to mind.

[alcodiesel]

Just joking, Neil. Reliability is a top concern. If I need that engine to run, I need it to run! I appreciate your suggestions and help. You have always ( 6 years) been there for me. Thank you.

Here's what I came up with:


Voltage at the coil [ + ] terminal at cruising RPM 7.4 Volts

Primary winding resistance of the coil 3.9 Ohms
(terminal to terminal, [ - ] wire removed)

Recommended resistor -1.7 Ohms
No Resistor Recommended

[ndutton]

Well, you're not gonna like this. At 7.4V to the coil your engine shouldn't even be running. Years ago when we were doing testing to establish a practical trip threshold for the EWDS we found engine performance dropped off significantly just under 9 volts - - - and that was at idle! Please repeat the coil input voltage test between coil + and a solid block ground. For the re- test, twist or 'drill in' the test probes to eliminate the resistance of engine paint, grime, corrosion and rust. Be aggressive with the probe points.

While you're at it, please measure the alternator output too. It should be somewhere around 14 volts. That will establish confidence in the alternator, test technique and meter accuracy, a good baseline.

[alcodiesel]

Woah, I measured between Coil + and coil -. Sheesh, do I feel like a dummy.

[ndutton]

I thought you might have. It's correct for measuring coil resistance (wires removed as you said) but not voltage. Despite how it is identified, the small coil '-' post is not a ground.

Run the calculation again with the new voltage measurement. Voltage is expected to be in the range of 13~14 volts. I expect the end result to be the same, "resistor not required."

[alcodiesel]

Neil the Atomic 4 Whisperer:


Voltage at the coil [ + ] terminal at cruising RPM 13.5 Volts

Primary winding resistance of the coil 3.9 Ohms
(terminal to terminal, [ - ] wire removed)

Recommended resistor 0.1 Ohms

Major feeling of confidence. Thank you

[ndutton]

Bill, I wouldn't fuss with an added resistor if I were you.

Respecting good engineering practice, the calculator adds a 15% margin of safety below 4 amps (3.4 amps target) and your setup calculates to 3.46 amps. You're good right where you are.

[alcodiesel]

Thank you Neil. I was thinking the same thing. Gee wiz a tenth of an ohm? What's that like? a breath of warm air vs. cold air?

This E ignition comes from Indigo and has a resistor strapped to the coil. All PO stuff. Tom was saying it should be OK. Now I know it is OK.

[ndutton]

In that case I defer to Indigo Electronics. It's best that they specify the recommended amperage for their product. The advice and calculator I provided here pertain to the EI product Moyer Marine offers following the manufacturer's published advisement and our testing. Indigo may choose to follow the same specification but that is for them to say.