There are three styles of master switches on the market, all available from
Racers Wholesale and others.
I've been vintage racing for years and years and have never had this
experience at tech inspection. They always check to see if brake lights go
out, as Irv says.
There are some technical considerations, though.
1. Two-post switch: If you connect the alternator to the engine side, then
the engine will still run even with the switch shut off. Also if you turn a
running engine off with the master switch, there is the possibility of
creating a spike that is harmful to alternators. If you connect the
alternator wire to the battery side of the switch, then the wire to the
alternator is always hot. That means that when you take off the exhaust
manifold with the alternator still on the car (notice I said 'when' and not
'if') and you touch the post with a wrench it makes a beautiful blue flash
and damages all metal parts involved.
2. Two-post switch that has two big posts for the whole system and a
separate two posts for the alternator. It is the most practical. That is
the one I install on customer cars. This switch causes the wire to the
alternator to go dead. I suppose it can cause the spike if a running engine
is shut off with the switch but haven't experienced that if the engine is
just idling, and I always test it once to make sure the thing is wired
correctly.
3. The six-post switch has provisions for taking care of all that stuff. It
does this by having an external low resistance resistor that gets switched
into the circuit to lower the voltage spike on shutoff. Although I have
that switch on my car, it is unnecessarily complicated, takes a lot of
wiring, and is more bulky and has more stuff hanging off the back of it.
I've just left mine on because I'm to cheap to replace it before it goes
bad, and when I need to change it for some reason, I'll install the one
described in 2 above.
At 07:24 PM 4/21/2005, Tom Walling wrote:
>I am helping a friend get a TVR Grantura (OK - just for the sake of this list,
>drop the middle "V") ready for vintage racing this season. Almost there, but
>that's a topic for another time and another list...
>
>My question is -- if the emergency cut-off switch is employed whilst the
>engine is running, is there any damage being done to the alternator (diodes)?
>The car does not have a generator, but it has an alternator.
uncle jack
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