Because there should be a ground wire for the box.

"Chris" wrote in message
...
the brown wire does go straight to the tach for readings I would suppose.
How could the tach affect the functioning of the switch for the engine
running?



"Bill McKee" wrote in message
link.net...
The brown is probably the ground wire. So you should be very concerned
about the brown wire, that of the 3 wires you are concerned about, none
is ground for the box.

"Chris" wrote in message
...
In my case there's four wires on mine.
Red with power in.
Blue with a connection to the distributor
Brown which goes back to the tach I believe
Green which goes to the + on the coil.

I can verify the Red as 12 volts in.
The brown I don't care about
The blue though I'm not sure how I could test the output or whatever
with how it works.
The green to the coil I'd love to test with a test light, but I'm not
sure what really comes out of there.


"tony thomas" wrote in message
news:y2Mne.9908$xm3.2581@attbi_s21...
Technically there is no way that I know of. However, there is a way to
verify all the signals coming into it are there and if the spark is
there. If all inputs are right and no output then you have verified the
switchbox is bad.

--
Tony
my boats and cars at http://t.thomas.home.mchsi.com

-
"Chris" wrote in message
. ..
I've heard from some that there are tools at the merc dealers to test
switch boxes, however, when I went to an old merc dealer who tests old
motors he said that there was no way to test a switch box.

Specifically, 70's era switch boxes.

Is this true?