PROJECTS TO IMPROVE YOUR BOAT BY TOM NEALE
A BRIEF MOMENT IN TIME
Momentary switches make generators and engines start
at the push of a button. But when they don’t start, consider
the switch rather than the component itself
AMOMENTARY SWITCH CAN COME IN NUMEROUS FORMS. You’re probably most familiar with the little push button on your panel at the helm. Let’s use the button for the horn as an exam- ple. You push it in and the horn blows. You take your finger off, it pops back out, and the horn stops blowing. Suppose the horn
doesn’t blow, or blows erratically, when you push the button in. The issue may
be corroded connections at the switch terminals or elsewhere. This is easy to
fix so check connections at the switch, horn, and power sources, before going further. If you
see corrosion or other impairments such as a loose connection, fix that first. This may be as
simple as tightening a screw or disconnecting the connection, cleaning it with an abrasive,
adding a squirt of moisture-disbursing oil, and reassembling. If you don’t see a problem with
the wiring and connections, suspect the switch.
If your horn won’t blow,
or blows erratically, it’s
probably the switch
that’s the problem.
FINDING THE FAULT
The basics of a momentary switch are fairly simple. The button is essentially a plunger held in
the out position within its casing by a spring. At the other end of the plunger (inside the switch
housing) is a contact surface. This is a metal conductor attached to the plunger, or pushed by
PHOTOS: MEL NEALE
(a) Momentary switch from a
horn — the wires attach to the
terminals at the base.
(b) Carefully opening switch by
bending back tabs.
(c) Removing terminal plate
from switch box.
the plunger, so that it contacts (jumps) and
thus connects the back ends of the two wire
terminals. The circuit is completed and the
horn blows. When you remove your finger,
the spring pushes the plunger back out and
the contact is broken.
You can usually determine quickly if the
switch itself is the culprit by carefully jumping the wires, which are connected to the
terminals behind the switch. Simply remove
one wire from its terminal and touch it to
the other. This normally causes a spark, and
sparks cause explosions and fire unless the
area where you are working is completely
free of combustibles, including gases. You
can also get a small shock if you’re not
careful. Some mechanics use an improvised
jumper wire, which is a short piece of well-insulated wire with terminals at each end
and a positive on/off switch in the middle.
You turn the wire switch off, connect the
wire ends to the momentary switch terminals, turn the wire switch on, and this more
safely jumps the terminals. This wire and its
on/off switch must be heavy duty enough to
safely conduct the current involved. (If you
have any doubt, get a qualified professional
to do this simple check.) If the horn blows
when you jump the wires, your issue is probably in the switch.
You can also test the switch, in theory, by
removing both wires and using a volt-ohm