Confusion!
That bulletin is a bit confusing because it swaps around the terms, "switch", "solenoid", and "relay" interchangeably.
Well, they ARE the same thing. A magnetically controlled switch IS a relay, and a relay IS a magnetically controlled switch, and when we are talking about automotive starters, both of those terms are interchangeable with the term, "solenoid". They are all the same thing.
(NOTE: Properly speaking, "solenoid" is not quite the same thing. A solenoid can be used as a switch,
and for many other things, but the automotive world has taken it to mean, "magnetically controlled switch". It's not very precise, but oh well.)
Okay, let me try to sort it out.
Remember what a relay does - it allows us to use a low-current circuit to switch a high-current circuit. The starter solenoid does exactly this - it's
functionally the same thing as the under-dash relay.
So why have two?
Wire size and current capacity.
Hold that thought, and let's go back in time a bit.
My parent's '48 Chevy that they had when I was little (it was old already, okay?), had a starter switch on the floor. When the key was turned, all that happened was that the ignition circuit was completed. The car could have been manually cranked over at that point, or push-started. Nothing happens with the starter motor.
When Dad stomped on that big switch on the floor, that humongous switch closed and current flowed to the starter motor.
There was no relay, no starter solenoid. All that starting current was handled by the starter switch. To handle that current, it had to be huge. WAAAY to big to fit in a keyswitch on the column!
As time when on, somebody decided to include a relay (solenoid) on the starter, so we could send some jolts to the starter motor via the key switch.
Great! Much easier!
But wait a minute. That solenoid is a big electromagnet, driving a spring-loaded electrical switch. It needs electric current to operate it. It doesn't require anywhere NEAR as much current as the starter motor itself, but it's still more than we can send through the key switch. Maybe it takes 20 or 25 amps or so. (Guessing here, but that's probably in the ballpark.) We really don't want to run that much current through the keyswitch. We'd need some big wires, and we'd have heat and size issues with the switch.
Hmmm. Okay, let's use a smaller relay to drive the solenoid. We can use a relay that needs only an amp or maybe a quarter amp to work, and still carry 30 amps or so of current. (A typical Bosch relay needs a quarter amp, and can be rated up to 40 amps.) NOW we can have small wires going to the keyswitch, and no heat or size problems with the keyswitch.
And we get enough current through that smaller relay to drive the big electromagnet in the solenoid.
So that's what we have in modern vehicles, including our CUCVs. We have a smaller relay under the dash (or under the hood somewhere), driving a bigger relay (
which we call the solenoid) on the starter motor. These are two different circuits which work together to turn the starter motor.
That 200 amp reference is ONLY talking about the circuit that provides current to the starter motor. This is switched by, and flows through, the solenoid. It does NOT flow through the under-dash relay.
Based on what I've read here about burned contacts in the OEM relay, it sounds to me like that relay was a bit undersized. That's why the Doghead relay cures the problem. It's built to handle a LOT more current than is required for that circuit. It's massive overkill, really. That makes it much more reliable than the OEM relay.
So, Doghead is right on the money. That bulletin has nothing to do with the Doghead relay. It's talking about the wiring from the batteries to the solenoid on the starter motor.
As to why electrical motors burn up - there are a few reasons that can happen.
- Too much voltage
- Too little voltage.
- Too much load.
That bulletin is really addressing #2, too little voltage. If your wiring is too small, you'll have too much voltage drop by the time you get to the starter motor. That makes them work too hard, and shortens the life.
