Dumb Starter/Battery Question

[88911coupe]

OK...I've been reading dozens of threads on starter issues (there are a zillion) and one thing eludes me. I'm fine with mechanical things but electricity still confuses me so here goes, hopefully my question makes sense. How/where does power for the starter ('88 Carrera in my case, if that matters) flow from the battery to the starter? I've been looking at diagrams that may as well be hieroglyphics (sp?) and can't really picture it in my mind. It's not from the "yellow" wire is it? What causes there to be power delivered to the starter when starter in "start" position? What is the circuit that's completed?
Maybe a dumb question but I had to ask since I'm fighting random non starts on my car.
TIA,

[Joe Bob]

BIG RED CABLE, is your direct lead from the + side of the battery and connects to the solenoid. Terminal 50, energizes it thru the ignition switch.

Looking at the solenoid, the BRC is at 9 0'clock, terminal 50 at 12.

[911pcars]

As JB says.

An add'l explanation: The ign. switch energizes the solenoid which acts like a HD switch (lots of current flow from battery to starter motor). It also extends a gear to engage the engine as the starter motor begins to rotate.

Sherwood

[Joe Bob]

Yeah, the solenoid is a BIG relay. The click you hear is the solenoid getting power, extending the drive gear....(edit not shaft) out, coming in contact with the ring gear, the end of the shaft extends into the trans and hopefully a good brass or bronze bushing keeps it from flexing......

Solenoids have a dielectric grease that can turn to mud....hot start issues can be fixed by rebuilding or replacing the solenoid or adding a "Hot Start" relay that bumps voltage to a higher level. I'm not a fan.....of the relay 'fix'.

[88911coupe]

OK, thanks...so when people refer to poor connectivity or voltage drop on the yellow wire it is hindering the power to the solenoid, not the starter, per se. The solenoid's functions are powered by the yellow wire...correct?

[Joe Bob]

The yellow wire turns the solenoid on so that the red wire can do it's job.....the red wire provides the juice from the battery...hence cranking power.

Have you ever used a screwdriver to jumper the two posts when the ignition switch is bad?

[911pcars]

Originally Posted by 88911coupe

OK, thanks...so when people refer to poor connectivity or voltage drop on the yellow wire it is hindering the power to the solenoid, not the starter, per se. The solenoid's functions are powered by the yellow wire...correct?

At some voltage level below a threshold voltage (normal is about 12V), the solenoid will not energize via the ign. switch (yellow wire). This is exacerbated by the long distance from ignition sw. to solenoid and/or loose/dirty connections in this electrical path.

An "add-on" relay can operate at reduced voltage to, in effect, provide a shorter electrical path from battery to solenoid. Recall that the large battery + cable is poised at the large solenoid post waiting for the solenoid to engage. This also provides a voltage source to help energize the solenoid.

Sherwood
Remote Starter

[Joe Bob]

The dumass way to check a starter.....

[Joe Bob]

[911pcars]

I get it, but why do so many YouTubers have only one arm/hand? Do only the physically challenged contribute?

The fumbling around to proceed through an obvious two-handed task doesn't inspire a lot of confidence. The "head peeking over the fence" intro. is typical. A $10 tripod would make a world of difference. There were some edits, so the videographer had some rudimentary skills.

A slight correction to the last video which otherwise provides some good info.
The drive gear assy. they show is not a "Bendix" drive but an "over-running clutch".

Bendix drives are used on Ford-type starter motors (not shown in video) He shouldn't have tried to fake it. The solenoid (aka HD relay) is remotely mounted (typically in the engine compartment) and merely provides the switching in the battery + cable to the starter. Will save the Ford-oriented description for the GT-40 crowd for another time.

I won't mention the grease-infused parts (but I just did).

S

[Joe Bob]

Didn't mention the shortcomings of his commentary but your points are valid.

BTW, The hot start relay fix for both the Bosch SR17 and 68 starters....was actually a Ford relay.

[Joe Bob]

What I used to do on VWs......

[88911coupe]

Wow, very useful explanations and the video is great as well.

[911pcars]

Originally Posted by Joe Bob

What I used to do on VWs......

In the above modified circuit, a HD Ford-type "solenoid" isn't necessary. A light duty, 30A relay will suffice (Bosch or otherwise). All the starter solenoid needs is a reliable source level of 12V to energize. High current not required to do that.

S