Starter current draw on ’56 Big Twin 30

[wet-willie]

I’d like to know how many amps the starter draws while cranking so I can determine what the minimum gauge wire has to be for the battery cables.
FWIW, the spec sheet for the motor doesn’t have this information.
Thanks!

[frankr]

Diagram says #4 cables

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[wet-willie]

Thanks Frank. Excellent schematic! Looks like I’ll be ordering some 4 gauge battery cables.

After examining the schematic, I have 2 more questions you, or someone else, may be able to answer.
Re: the black wire that runs to the mercury safety switch. Where does the current or signal go from there? It doesn’t show a ground or the completion of a circuit.
I also notice the battery is 6 volts. Am I doing any harm by using a 12 volt battery? As I’d expect, it spins the starter very nicely and stays charged too.

Thanks again.

[mini-motors]

The black wire is the ground. The red wire is the hot.

[chris-p]

The starter will handle the 12 volts fine. The choke solenoid will fry though. You can convert the wiring to run on a 12 volt battery, and starter solenoid. Or, you can wire in a resistor. Your choice. I like to wire them for 12 volts, then sub in a 12 volt battery, 12 volt starter solenoid, and a 12 volt choke solenoid from a ’57 and up motor.

The Mercury switch is the ground, when the throttle is at the START setting, other wise not, and the motor will not start.

[wet-willie]

I knew the black wire was the ground. I also knew the purpose of the mercury switch. What I was asking about is why the schematic doesn’t show the mercury switch being grounded. Just curious.
I’ll have to contact the PO of my motor and see if the starter and choke solenoids have been converted. If not, I’ll consider myself very lucky that I haven’t fried either one.

[Mumbles]

The mercury switch finds ground thru its housing and clamp screw, same as the choke solenoid does.

[frankr]

quote Mumbles:

The mercury switch finds ground thru its housing and clamp screw, same as the choke solenoid does.

That does bring up a good point. Early models had problems with intermittent grounding of the mercury switch circuit due to reliance on making good contact through the throttle shaft gear which is loose enough to rotate freely. (Edit: A flat spring, #68 in the inset box, was supposed to make the shaft ground.) On later models, a ground wire was added between the mercury switch and steering bracket. Also, the steering bracket has a ground wire (#72 in the inset box) to the motor frame, which is not shown on the diagram. That ground is necessary because the steering bracket is mounted on the rubber mounts.

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