Occam's Razor

[hcrisp]

Spring start up (late)

A4 won't start. Don't lay on the starter, start sleuthing:

Facet fuel pump no tick-tick. Zero pressure on fuel pressure gauge, just installed and for one second thought this was the cause.
Jump the OPSS. No tick-tick.
Connect fuel pump to starter solenoid: TICK-TICK.
Connect fuel pump to coil+. Tick-tick and A4 RUNNING.
Now we are down to the wire between the coil+ and the OPSS. Wait, I see a fuse in-line there...

[Al Schober]

So? Was it the fuse???
Helped my son with his Jacuzzi - fried wire between the contactor and the heater (220V, 30A). Heater tested good, but the connections were corroded.
Just for fun, I did a spreadsheet with different values of contact resistance to see what kind of power the resistance would generate. I was surprised to find how little resistance is need to develop significant heat - ie: less than 1 ohm developed over 100 watts of heat!
Perhaps a poor contact to the fuse developed enough heat to cause the fuse to pop?

[hcrisp]

Yes, it was the fuse. I think you are right, Al. The connection from the coil+ at the OPSS was very loose. It wasn't sloppy when I made that wire - Ancor connectors are very good quality and I will continue to use them.
Replaced fuse and connector.
It's possible I shorted when fussing with the jumper?
I switched to the electrical side of the problem when the A4 started immediately after I forced fuel to the carb (temporary squeeze bulb, now removed).
I ran the carb dry last Fall. Maybe it's better to leave fuel in the lines over the Winter?
In retrospect, even with the launch delay, the whole experience was enjoyable and also reinforced my essential tools to have onboard list.

[JOHN COOKSON]

I use a bit of dielectric grease (or what ever you call the stuff) on my OPSS connections to hold down the corrosion a bit.
It seems to me when there is two metals hooked together and they are passing electric current corrosion happens even faster.

TRUE GRIT