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I have a horizontal shaft Briggs model 190407 8hp electric start points ignition engine. and it has duel alternators. I have it wired to the exact key switch in this diagram and followed the diagram. It starts shuts off and appears to charge. But the gauge pegs past 15 amps while the engine is running. I have a very small battery and it starts the engine fine. I havn’t ran the engine very long because I’m not sure if the pegged amp gauge is causing damage. I was reading about a diode. I think mines under the flywheel? can someone tell me at what voltage and amps this engine should make to safely charge my battery? And the other alternator is the lights?

See the alternator there? It is actually 2 separate windings, where one winding is of fewer turns but a larger gauge wire and powers the headlights through AC current, and the second winding has more turns and thinner gauge wire, except it has a diode to rectify the AC to DC and charge the battery. 15 amp rate of charge for a simple diode alternator does sound high, and if it was in fact charging the amp meter current should start to drop pretty fast. It sounds like there is a short to ground somewhere on the charging wire path. What happens when you have the key on but it isn't running?

artemjemmy said:

See the alternator there? It is actually 2 separate windings, where one winding is of fewer turns but a larger gauge wire and powers the headlights through AC current, and the second winding has more turns and thinner gauge wire, except it has a diode to rectify the AC to DC and charge the battery. 15 amp rate of charge for a simple diode alternator does sound high, and if it was in fact charging the amp meter current should start to drop pretty fast. It sounds like there is a short to ground somewhere on the charging wire path. What happens when you have the key on but it isn't running?

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The amp gauge pegs when I turn the key to on not start position. When starting it drops near zero and when the engine starts the gauge automatically pegs again. I have followed that wiring diagram perfectly. I also let the battery charge all night and it’s new. the charger kicked off before morning. Plugged it all in and the gauge is still pegged when running. I looked through the wiring and couldn’t find anywhere it could short? Also does the amp gauge and key switch need to be isolated? I have it screwed to a metal dash. I don’t wanna melt wires or get shocked or something.. Edit: I don’t even know if the wiring diagram is right for my horizontal 8hp

I was looking at the wiring how does the amp gauge peg when it’s on the ac line? The engine is not running?? The ac line goes directly from the diode wire to the key switch with a gauge in between it all.. how could I get a bunch of amps through that line when it’s not running?

If it pegs even when it isn't running then you have your amp meter installed backwards or you are reading it wrong. Since the alternator cannot possibly be doing anything when it isn't running then that current must be from the battery discharging. Assuming that diagram is 100% accurate, then current is flowing back through the alternator, which could really only mean your diode is shorted and is conducting both ways.

artemjemmy said:

If it pegs even when it isn't running then you have your amp meter installed backwards or you are reading it wrong. Since the alternator cannot possibly be doing anything when it isn't running then that current must be from the battery discharging. Assuming that diagram is 100% accurate, then current is flowing back through the alternator, which could really only mean your diode is shorted and is conducting both ways.

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Just went out and Hooked up the meter backwards. It just pegged the other way.. so there is amps running through the ac line while not running. The diode is under the flywheel right? It doesn’t hang external to the engine block? I’m using a six post switch. I have a five post switch I can test but don’t know if this wire is needed or not for the four post switch.. It’s blocked unlike all the other solid running connections.

Briggs10102 said:

Just went out and Hooked up the meter backwards. It just pegged the other way.. so there is amps running through the ac line while not running. The diode is under the flywheel right? It doesn’t hang external to the engine block? I’m using a six post switch. I have a five post switch I can test but don’t know if this wire is needed or not for the four post switch.. It’s blocked unlike all the other solid running connections. View attachment 58506

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I have no idea where a diode would be on the engine you have because of how old it is but newer intek vertical shaft engines have the diode just a little ways back from the engine electrical connector, next to the dipstick.

Have you considered that the amp gauge is faulty ?
I seriously doubt that your alternator could pump out 15A if it's life depended upon it
Next Amps is a measure of flow so you only get 15 Amps coming off the alternator if there is a load that can draw 15 A
So either the amp gauge is toast , the battery is toast or their is a direct short to ground on the charging circuit.
Easy test is to get a auto globe of known wattage then undo the alternator wire that goes to the solenoid and hook the globe up to it .
Divide the wattage of the globe by 12 ( volts ) and that is what the amp gauge should show
Blinker globes would show around 2A for example

bertsmobile1 said:

Have you considered that the amp gauge is faulty ?
I seriously doubt that your alternator could pump out 15A if it's life depended upon it
Next Amps is a measure of flow so you only get 15 Amps coming off the alternator if there is a load that can draw 15 A
So either the amp gauge is toast , the battery is toast or their is a direct short to ground on the charging circuit.
Easy test is to get a auto globe of known wattage then undo the alternator wire that goes to the solenoid and hook the globe up to it .
Divide the wattage of the globe by 12 ( volts ) and that is what the amp gauge should show
Blinker globes would show around 2A for example

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I think he was saying that the amp meter pegs even when the engine is not running, so there is current flowing through the charging circuit even if it isn't charging, which must be the battery discharging.

If the amp gauge was fried, it might read current where there is none but it wouldn't be able to detect being hooked up backward (pegs the other way) unless there was something to detect.

Diode is most certainly toast. Might be other problems too.