3 Wires along the firewall going to the starter for 1939 Cadillac Series 61, what are two smaller wires for?

[dennisspeaks]

On my 1939 Cadillac Series 61 the cloth taped 3 wires that go from the main engine wire harness that goes to the starter, there are two wires that look like 12 gage and one that look like 10 gage. 

My question is what are the two smaller wires for?  One of the previous owners done some wire modifications and it looks like the two smaller wires are disconnected.

Thanks in advance for your help.

Dennis

[Tom Boehm]

Here is how my 1940 Lasalle is wired. I have not yet installed the wiring harness. I was able to easily trace the temporary wires. I verified this is correct by consulting the wiring diagram in the 1939 Cadillac shop manual. 

There are 4 terminals on the starter. 

The 2 big ones with nuts on the starter solenoid:

     The one closest to the block is a copper strap to the starter.

     The other big one with a nut has 2 wires on it. One big cable to the negative battery terminal. One wire to the ammeter on the dashboard (10 gauge wire orig.)

Two smaller terminals with screws on the starter relay:

     Front one/right one goes to the middle terminal (generator) on the voltage regulator on the firewall. (10 gauge wire originally)

     Rear one/left one goes to the starter button on the dashboard. (16 gauge wire originally)

 

I am not good at electric but I imagine you could use a continuity tester to find where the loose ends at the starter are connected to at the other end. Then you can connect them to the correct terminals according to the instructions above. 

Edited February 26 by Tom Boehm (see edit history)

[Oldtech]

Reading your description I'm not sure about that wire to the GEN connector on the regulator.  If this is correct what does it do? Anyone? 

[Tom Boehm]

Another wire from the generator connects to the same terminal. 

[Brass is Best]

A shop manual and wire diagram would clear this all up.

 

[Bloo]

8 hours ago, Oldtech said:

Reading your description I'm not sure about that wire to the GEN connector on the regulator.  If this is correct what does it do? Anyone? 

I have a guess. To understand it, pretend for a moment it is a Buick with automatic starting (gas pedal start).

 

The connection at the back of the starter don't go directly to the solenoid. They are a relay coil. The relay triggers the solenoid. To engage the starter, you must provide power to one terminal and ground to the other. On a Buick, power is provided to one terminal by the vacuum switch and the throttle switch, in series. The throttle has to be depressed AND there has to be no vacuum for the starter to come on. I imagine you are familiar with all of this.

 

But, what if you are going up a steep hill with the throttle to the floor? Your foot is on the throttle and there is no vacuum. The starter might engage. Buick solved this in the mid 30s by adding an extra contact to the voltage regulator labeled "GRD" that is only grounded when the system is not charging. If you are barreling up a hill the generator should be charging, and the cutout engaged. The "GRD" terminal is disconnected from ground inside the regulator, and there is no ground for the second starter relay terminal. The starter can't accidentally engage.

 

Around 1939, those special regulators were no longer a thing, and Buick started connecting the wire that had been connected to the "GRD" terminal to the "GEN" terminal. When the generator is not charging, and the cutout is not engaged, there is a fairly low resistance path from the "GEN" terminal to ground through the armature windings and the brushes. The starter relay has a ground and the starter can work. Once the generator starts charging, the "GEN" terminal is at charging voltage, and there is no longer a ground for the starter relay.

 

I don't know why they would have bothered running the second starter relay terminal to the regulator on the Cadillac if they were using a starter button to provide voltage to the starter relay. It would prevent you from pushing the button and grinding the starter on an already running engine if you were underway, but if the car was slow idling, and the generator was not charging, you still could grind it if you hit the button accidentally. It seems like slow idle would be the most likely time for someone to hit the button, not realizing the engine is already running.

 

 

Edited February 27 by Bloo (see edit history)

[Tom Boehm]

Like I said in my first post, I checked my car against the wiring diagram in the shop manual to verify it is correct. 

Here is a quote from the 1939 Cadillac shop manual:

 

"The starter is connected back to the generator in such a way that when the generator is charging, a reverse current flows through the cut out relay, breaks the circuit, and prevents starter engagement. The ignition switch is connected in series with the relay so the ignition must be turned on before the starter can be operated."

 

Let's wait and see if dennisspeaks, the OP, question is answered before we muddy the waters more. 

[Oldtech]

Thanks. I'm sort of familiar with the Buick setup. Didn't think of Caddy using it. 

[dennisspeaks]

Thanks for all your replies.  I have the DETROIT IRON DPRGM16339SM Shop Manual  and DETROIT IRON DPRGM5339FB 1939 - 1940 Fisher Body Shop Manual ordered from rock auto, just waiting for them to get here, was just trying to get some insight ahead of time.  I hear you Tom, I am not that good at electronics either just wanted to see what I can do on my own. 

[dennisspeaks]

Well the two books that I found came in the mail, unfortunately the flu caught me and I can't do anything.  Well at least it's not covid or RSV.

 

Are there any other books on these cars available..