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The relay benefits the starter by bypassing the ignition switch. It's a shorter more direct path from the battery to the starter than through the ignition switch.

Harold
This is not exactly accurate. The relay benefits the ignition switch by reducing the current draw across the switch when the starter motor is engaged. The solenoid itself is a relay, but the current draw to activate the solenoid is still substantial. By inserting a relay in the circuit, the current through the ignition switch to activate the relay is reduced considerably, a significant benefit to the ignition switch.

A relay consists of an electromagnetic switch that, when activated, causes a usually open switch to close that allows heavier current to flow through a second circuit that activates the target device (in this case the solenoid).

The Opel GT has a similar flaw in its horn circuit that does not use a relay. The horns draw a fairly heavy load and the result is the horn contact ring on the steering column becomes burned and pitted, to the point where it becomes inoperable. Installing a relay in this circuit is a fairly simple exercise that is well worth the small amount of time and cost.
 

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What i read that you wrote was that the starter benefits because the relay provides a shorter path for the electricity to flow. Given that electricity travels at roughly 186,000 miles per second, the length of the path is of little consequence. The importance of the relay is that it reduces the current load on the switches involved.
 

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What i read that you wrote was that the starter benefits because the relay provides a shorter path for the electricity to flow. Given that electricity travels at roughly 186,000 miles per second, the length of the path is of little consequence. The importance of the relay is that it reduces the current load on the switches involved.
Never thought about the speed of electricity. Apparently it's almost as fast as light.
It does reduce the current load on a switch. The relay for the starter is typically installed close to the starter, closer than the switch and with heavier gauge wire. The shorter path means less voltage/amperage drop to the starter, correct?
I recall reading an article where relays were used for headlights. IIRC, there was at least a 1V increase and noticeably brighter headlights. The same can probably be said about using a relay with horns, making them louder.

Harold
 

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The shorter path means nothing to the starter. The electromagnet inside the relay that activates the Usually Off switch, requires far less current than does the starter solenoid. Thus, the wiring is set so that the ignition switch activates the electromagnet. By activating the electromagnet, the Usually Off switch inside the relay closes, allowing heavier current to flow from an electricity source to the solenoid.

The OEM wiring for the Opel's starter requires a relatively heavy current draw through the ignition switch, that eventually deteriorates the switch to the point where it no longer works. The same is true of the horns that do not use a relay, but instead are grounded directly through the horn ring on the steering wheel. A very small change to the wiring system at the front of the car will allow you to insert a relay into the circuit.

By way of illustration, I have attached a diagram showing the internal workings of a typical relay used for automotive purposes. In this particular case, it is the horn circuitry for my Triumph Spitfire4.
 

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You're putting way too much effort into this. The main draw is going through the relay, correct? The ignition switch activates the relay, correct? Usually the shorter the run, the less the voltage/amp drop is. I'll admit it may be minuscule. The path is shorter through the relay.

I've added more than one relay into a circuit most triggered by positive voltage and one by the ground for an Opel horn.

Harold

P.S. If I'm not smart enough to understand how they work then I'm probably not smart enough to understand your schematic. ;)
 

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You're putting way too much effort into this. The main draw is going through the relay, correct? The ignition switch activates the relay, correct? Usually the shorter the run, the less the voltage/amp drop is. I'll admit it may be minuscule. The path is shorter through the relay.

I've added more than one relay into a circuit most triggered by positive voltage and one by the ground for an Opel horn.

Harold

P.S. If I'm not smart enough to understand how they work then I'm probably not smart enough to understand your schematic. ;)
Sorry Harold, it isn't "distance" at all. The advantage of a relay is simply the capability of the contacts. A typical 12 volt Bosch-style relay only requires a couple hundred mA to be actuated, but the contacts can handle (depending on the model) 30, 40, 60 or even 80 amps.

A starter solenoid is essentially a heavy duty relay capable of transmitting up to 100 amps to the starter, except the Opel (and GM) starter solenoids also drive the starter gear into the flywheel ring gear. But the Opel starter solenoid can draw a dozen amps thru the ignition switch contacts, which history shows they are not designed to do repeatedly.
 

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The point I was trying to make is the travel distance of a lighter gauge wire through the ignition switch back to the solenoid vs a heavier gauge wire carrying the voltage directly to the starter solenoid. Yes one of the advantages of a relay is that a cheaper or lighter duty switch can be used to trigger the relay. Heavier duty relays are generally cheaper than the same amperage switches. The longer the electrical run the heavier the wire gauge needs to be especially if it's going to have a high amp draw. Otherwise I would run a lighter, cheaper less bulky wire to everything, even the relays.

Harold
 

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Voltage has nothing to do with the equation. If it did, you would need a cable as thick as your wrist to go from the coil to the distributor cap. It is the current draw, the amps, that matter. The OEM wires in the circuit are not the weak point -- the weak point is the contacts in the ignition switch that are subject to wear over time because because of the current load across those points. The fix is to insert a relay in the circuit so that the ignition switch contact points are carrying a much smaller amperage load. As for the other side of the relay, the side carrying the heavier current from a current source to the solenoid, you can put that anywhere -- distance does not matter. If distance mattered, why would the headlamp and dimmer relays not be up front closer to the headlamps?

Frankly, your earlier post suggested that you do not fully understand how a relay works, other than "by magic" and I thought an explanation would be helpful. As to my attached diagram, that others have found helpful, what is there not to understand other than the electromagnet, when activated, attracts the usually open switch to the closed position, closing the circuit between terminals 30 and 87? If you feel that I insulted your intelligence, knowledge and experience, then I apologize -- I was simply attempting to offer information.
 
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