How To Replace the PMC Rotary Switch With a Toggle Switch
By Rob Robinette
The PFS Powertrain Management Computer (PMC), also known as EFI's PMS, comes
with a large rotary switch for changing boost to low, medium and high settings.
The switch is so big it is hard to mount. I decided to replace the switch with a
small, 3-position toggle switch installed in the ashtray.
The 3 position toggle switch
I pulled out the Ohmmeter to find out how the PMC's rotary switch worked.
The switch has 3 wires connected to it. A red wire connected to the center
connector, and a black and a white wire connected to two peripheral connectors.
I discovered that when none of the wires are connected electrically by the
switch, the PMC is in the low boost configuration. When the red and black wires
are connected, the PMC is in the mid configuration, and when the red and white
wires are connected the PMC is in the high boost configuration.
I then went to Radio Shack and picked up a Toggle Switch, Radio Shack Cat. No. 275-1545, Mini DPDT Toggle Switch
(center off position), for $3.99. The switch is small enough that if you shorten
the switches toggle lever, you can mount it in the ashtray for a clean, total
stealthy look.
Start the install by popping the ashtray out by simply pulling it straight
up. Then pull the top of the center console loose by pulling it straight up. I
grabbed it at the shift boot and popped it up and then pulled the corners up.
To allow the ashtray door to close, you'll have to grind (or cut) the toggle
switch's lever to 1/3 of an inch long (.33"). You can make it really short
and it's still useable. I held the switch lever with a pair of needle-nose
pliers and ground it down using an electric drill and a small grinding stone. A
Dremmel tool with a cutting disk would work too, just be sure to hold the switch
by the lever when you grind/cut it.
Upside down ashtray with toggle switch installed
The ashtray's bottom below the little shelf area inside the ashtray where I
wanted to install the switch isn't flat and the plastic is too thick for the
switch. So I ground off some plastic from the bottom of the ashtray to flatten
and thin it. If you don't remove some plastic the switch will extend too deep
and prevent the ashtray from fitting into its receptacle. I drilled a 7/32"
hole in the little shelf, then reamed the hole out just a little until the
switch screwed into the hole securely (remove the switches top cap nut and
washers, you won't need them). If you do it right you will get a nice tight fit
that doesn't require the switch's cap nut to hold the switch in place (see
photo). Doing it this way will prevent the switch from sticking too far below
the ashtray (which will keep the ashtray from fitting in its receptacle) or too
far into the ashtray (which will prevent the ashtray from closing).
Toggle switch wired and soldered
Drill a 7/32" size hole in the center console's ashtray receptacle at
the leading edge (see photo). Cut the rotary switch off the wire from the PMC
and run the wire under the left passenger seat rail, under the carpet flap just
below the console, then under the main console and through the hole in the
ashtray receptacle.
Solder the wires to the toggle switch: red in the center and the black and
white on either side (see photo and diagram). The toggle switch has 2 rows of
connectors, just choose a row and put all 3 wires on that side. Solder them with
the wire coming into the switch from the front side. If you attach them to the
bottom of the connectors the switch will be too tall to fit into the ash tray
receptacle (see photo)
.
The finished installation
Pop the center console back down, feed the excess wire into the console,
insert the ashtray and have fun.
Rob Robinette
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