REPLACING THE OEM FANSTAT
The OEM fanstats in our beloved SabMags are set to conduct
electricity at 100C, or 212F. If you're interested in swapping
your OEM fanstat out for any of the ones listed here in the FAQ
as alternatives, the task is simple enough, but here's a few
things to be aware of.
First off, the OEM fanstats on the various vintage SabMags
came in at least two basic varieties: single-contact and
two-contact. In the single contact configuration, the fanstat
acts as a switch (like any fanstat), but the electrical path it's
switching is between it's single contact and ITS HOUSING. Thus,
if you put an ohm meter (DVM, multimeter, etc.) between the
fanstat's metal housing and the contact, you should read no
continuity (open circuit) at room temperature. However, in your
radiator, once the fanstat gets to its set temperature, it
conducts electricity through itself to the radiator that it's
In single contact fanstats, there's a ground wire brought to
the radiator housing itself. The purpose for this is simple; the
the radiator's mounting hardware is not designed to ground the
radiator to the bike's chassis, but to hold the radiator on. The
wire coming from the negative side of the battery grounds the
radiator. Thus, when your fanstat conducts electricity, it allows
that grounded radiator to send it's ground path to the fan. The
other side of the fan is always hot (+12vdc).
In the dual-contact fanstat, there's (obviously) two contacts.
This fanstat is "electrically isolated" from the
radiator, ie: there's no conductivity from either of those
contacts to the housing of the radiator, at any temperature. The
switch path is in one contact and out the other (doesn't matter
which way they're wired at all, since the switch is completely
passive). In this case, the negative side of the battery's wired
to one contact (ground) and the other contact is connected to the
negative side of the fan. When the fanstat conducts, it just
closes the switch and allows the ground path to flow to the fan,
If you are replacing a single-contact OEM fanstat with a dual-contact aftermarket version, simply take the one wire that's already going to the original fanstat and put it on one of the contacts of the new one. Take the other wire (that's going to the chassis of the radiator) and move it over to the other contact on the fanstat. A diagram for this is shown
If you're replacing a dual contact OEM with a single contact
aftermarket (not very common), just do the opposite of the
Now, some OEM fanstats had flat (blade) type "spade" contacts, while others had round (bayonet) types. If you buy a fanstat which has a different type of contact from what the wires originally had crimped on them, don't sweat it. Both sets of contacts are available from any auto parts store or Radio Shack. Just cut them off and crimp the appropriate ones on. If you don't have a decent electrical crimper, most hardware stores and all Radio Shacks sell them for anywhere from $8 to $200.
Unless you're planning on doing this regularly, buy a cheap one.