1 Topic by Lemon_Newton-Metre (edited by Lemon_Newton-Metre 2023-12-25 11:25 AM)

  • From: Elverson, PA
  • Registered: 2017-08-15
  • Posts: 1,132

Topic: Alternator wire to starter (follow-on question)?

Creating a separate thread because of my ignorance (though I think the previous: (Starter Switch) is a really useful discussion, I have at least one follow-on question as I'm looking into a push-to-start system right now):

What's the purpose of a wire from the alternator to the _starter_?

Do all/most vehicles have such a wire? Is it that a battery doesn't have enough energy by itself to start a vehicle, and it needs an assist from what little an alternator produces until the engine runs?

Clearly, I've never traced all the wires from an alternator.

I thought - as a general rule - a battery is an energy store which would power a starter and an electrical system, including an engine control and ignition system if there is one (I have a predilection for diesel vehicles) until the engine is running, at which time the alternator would take over, power the electrical and ignition systems, and recharge the battery.

I'm ignorant about a lot of things, and I don't have experience enough to know generalities about vehicles except the ones I have personally - I'm not a mechanic.

A wire from the alternator to the starter surprises me.

I see - on one vehicle I have - a stock ammeter voltmeter (thanks Zacks) in the dash which shows voltage, and that voltage isn't immediately at full potential until "a while" after the engine's running smoothly. As an aside, it's a diesel vehicle, but I don't think that's the key difference. I could be wrong.

2 Reply by Zacks (edited by Zacks 2023-12-25 11:06 AM)

  • Zacks
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Re: Alternator wire to starter (follow-on question)?

I'm guessing you have a thick high amp wire from battery to starter and starter to alternator with both terminals stacked on the starter post to effectively tie the battery to the alternator using less wire.

Most vehicles tie the battery to the alternator and the battery to the starter (so wires meet at battery.   It shouldn't matter, basically depending on the physical layout of the parts in the car one way uses less wire than the other and we are talking thick high amp wire so kinda expensive.

The alternator doesn't provide power until engine is spinning.  Probably just after starting the battery is "low" and demanding enough power it takes a sec for alternator to catch up.  Some vehicles control the alternator using a pcm signal so may not command charging at full voltage until rpm is stable to prevent spikes, but I didn't think Saturn did that...

For the record an ammeter is different from a voltmeter, if your dash displays volts its not an ammeter.

Most vehicles also get power to the fuse box and then modules after the battery.  ie battery is in between the alternator and fuse box because the battery is true DC power and will help absorb ripple left over from rectifying the AC current produced in the alternator.

  • From: Elverson, PA
  • Registered: 2017-08-15
  • Posts: 1,132

Re: Alternator wire to starter (follow-on question)?

Got it - thanks.

My question more related to the description of the wiring diagram in the referenced thread.

I know that an alternator connected to a battery, and the battery then connected to the starter, makes the alternator connected to the starter - I get that.

And I haven't seen an alternator wire as thick as the cables from a battery bank to a starter, or the cables connecting two batteries.

I was just confused by a description of a diagram showing an alternator wire directly connected to the starter.

But I admit, I've seen some strange directions printed recently; including directions that asked me to mount a bracket effectively 'backwards' according to the diagram, but the picture of the bracket was - as best as I can guess - a mirror image of the actual bracket. It mounted properly and works, but the diagram was wrong.

4 Reply by Zacks (edited by Zacks 2023-12-25 06:44 PM)

  • Zacks
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Re: Alternator wire to starter (follow-on question)?

Yeah I mean I assume the battery is NOT directly connected to the alternator but instead the starter is connected to battery and then the alternator picks up power fro. The hot lug on the starter.


I just pulled the wiring diagram, and yeah that's how it works.  1 wire from battery to starter, and 1 wire from alternator to starter.


Battery---‐----------------starter-----------------------alternator

But that's a hot all the time wire, unrelated to your issue, solenoid control wire (hot in start only) comes from the relay and is the purple wire.

The diagram doesn't show a ground wire because the starter is case grounded to the block.

  • From: Elverson, PA
  • Registered: 2017-08-15
  • Posts: 1,132

Re: Alternator wire to starter (follow-on question)?

Thanks, but my question related to the discussion by jimbooth in the referenced thread regarding his diagram from his starter relay issue; it's not my issue.

I posted my question because I was confused, and frankly, because I'm ignorant about general electrical connections and the starter on vehicles I haven't seen.

It was more a question for me to learn some big picture concept, not about a problem I have.

In general, what you wrote supports much of what I've seen.

And shortly I'll have a push-to-start kit, so I'll be able to read the instructions and look at the diagram. And hope it's better than the one I referenced above.