Technical SBC runs and sputters for 10 seconds after keys shut off...

If you haven't started working on it yet. First disconnect the fan as suggested. If that doesn't fix the problem,try disconnecting the heater fan next. Like your Dad said.Simple things first.

 

This is likely one of two problems, too high an idle speed, or too much initial timing. Try setting down the idle first

 

IF you use the temp sensor, you will wire it a little different. You will wire the relay ground to the sensor. then, the power feed as usual and the 12v to ign or acc on. The sensor will trigger the ground circuit when temp comes up.

typically this style will try to maintain a certain temp, if it is a 180 degree sensor, any time the motor is over 180 it will trigger the fan. once below it will shut the fan off. These do not offer a true come in/turn off temp range. it is either above the turn on temp or below. the fan function follows.
I have run plenty of these as well as the style with the probe in the radiator. The benefit of the probe style is that they are typically adjustable to allow different temps to trigger them on. I was taught old school, meaning that I like my fan to come on fairly soon/cool. I typically turn them on around 160 or so.

However, if you do not run any temp sensor to turn the fan on, you can run it with the ignition on. Although this may draw a little more electricity if not needed and delay the engine coming to full temp, it is essentially no different than any old engine running a mechanical fan. It comes on with the engine/ignition and off with the ignition. Unless a customer specifies other wise, I run mine to shut off with the ignition.

 

Done properly, it does no harm and can do a good job of de-carbonizing an engine. Get the engine to operating temperature and vary the RPMs by hand from a fast idle to maybe no more than half-throttle. While doing this pour a slow trickle of water down the carb, no more than what you would get thru a soda straw. An empty pop can works well for the task. Can just plain water really clean that well, I hear someone asking? Look at the top of the pistons and the combustion chambers on an engine that's been torn down for a blown head gasket...

 

I think if you take a look at the diagram on relay, Battery power comes in 30 and when switched on goes out to fan thru 87. Do not ground 87a. That is an additional switched output.
Relay diagram will also show where ground connects. Either 85 or 86 can be switched, or both. (example: switch power on, ground thru sender)

 

I've used these on cars in the past, back when you couldn't get a temp sensor at a rated setting....they always gave you a range when they would come on. Also he's local to me.

http://hotronicsproducts.com/product_info.php?products_id=27&osCsid=c5f61a0be7f103ab8b5fb08f090b41e5

 

I hear you. Just worried about the "done properly" part. If you tell somebody who obviously is new at this to pour water down their carburetor, you never know how they'll interpret that. Not to mention that there really wasn't any proof that the engine was carbonized in the first place.

 

Yep, this gets my vote - if there is is an electric fan.

 

Engine run on or dieseling is caused by to much air-fuel or heat. Eliminate one of the 3 and its fixed.