I will check my inventory of data on the old Snappers.
Are you replacing a Tecumseh engine with a Briggs or is it just replacing an old Briggs with a newer Briggs?
Gotta head to work now, so it may be tomorrow before I get back to this.

Are you replacing a Tecumseh engine with a Briggs or is it just replacing an old Briggs with a newer Briggs?
And, was the old engine electric start or manual start?
New engine electric start?
I have the answer but it will differ slightly depending on your answers to the above questions.

Thanks for your quick response. The original engine was a Briggs 11 hp and has been replaced by a newer 12 hp Briggs. Original engine was electric start + pull while the replacement engine is only an electric start.

That Red wire would go to the M terminal of the key switch and would provide shut down of engine if one of the interlock switches opened.
Since you referred to a "start button" your Snapper might not have a key switch with built in starter control. In that case, the key switch will be configured like the manual start version of schematic (where the key switch only controls engine shut down).
If you bought this Snapper "used", someone may have eliminated the Red wire circuit due to a failed interlock module (the thing with the red. yellow, and brown wires), or they wanted to defeat the interlock system.
Some of the earliest models differ in that a separate push button switch was used instead of a combo key switch to activate the starter.

Thanks again for the info. Checked the key switch and there is a single black wire to the engine; there is a separate push button to start the engine. The key switch does work to kill the engine. I am still confused as to where the red wire is supposed to attached to. It appears to be of the correct length to attach to the positive side of the battery --- does it attach there?

Thanks again for your help.

The single Black wire from the key switch is "likely" the kill wire to ground the coil. Is it grounded with the key OFF?

Typically, instead of connecting to the battery +, the Red charge output wire hooks to the + battery cable AT the starter solenoid. (same difference)
That's IF that is what the wire is-

Something else the wire may be is the "start" wire to the small terminal of the starter solenoid?

Possibly, if you list the old & new Model & Type numbers from the engines, we can determine which charging system they have.
Sometimes you can and sometimes.......

If you can take a couple more pictures, that can help. Sometimes when you get too close you can't tell where your looking at. (better focus would help too.)

I can guarantee that the red wire in question goes only to the circuit that is common to the M terminal of the key switch. M terminal, as in MAGNETO.
If your key switch has only a single wire going to it, that is the M terminal.
That is how the Snapper interlock set up works to kill the engine if you violate one of the parameters of the safety switches.
On your particular Snapper, the red wire of the interlock module probably made its connection to the magneto kill circuit on the engine throttle cable linkage plate.
On this linkage plate there is a nutted connector post where the kill wire from the key switch attaches. The red wire was most likely connected to this post, along with the wire leading to the magneto and the kill wire going to the key switch.
If the wire was not connected previously, it is because somebody disconnected it from the system.

This post was edited by mownie on Wed, Jul 24, 13 at 1:19

Thanks to all for you input. I will return to wiring this mower over the following weekend.

Monie is correct.

By the way joe3211. You have in your possion the best mower ever made. Don't loose it.

I appreciate all the above information which has helped me with lingering questions regarding my 3311X5S snapper I had bought used. It's equipped with an 11hp B&S engine with the exact carburetor linkage plate as shown in above illustration. On my engine I noted the single red wire coming from the interlock module had been disconnected from the carb linkage plate and has an alligator clip connected to it's end. My mower also has a two wired ignition switch with push button starter.

Question: I noted on the carburetor linkage plate illustration, a short white wire connected from the 'kill circuit stud' to a clip above the 'stud.' That wire is missing from my engine, but runs fine without it. Does anyone know the purpose of that wire connection? And what is that clip above the kill circuit stud? Thanks for any information.