DIAGNOSIS:
Fixing a bad backup light switch
PROCEDURES:
The Backup light switch is an expensive little beastie ($84
from Mr Badwrench) that is positioned high up on the ZF
transmission, making it difficult to get to. It fails more
often than it should. Here is a guide for the perplexed.
Why it fails:
The switch carries a fairly high current (4 Amps or more)
and is not protected by a arc-suppression capacitor or a
relay. Over time the contacts carbon up, and the resistance
across them goes from 0 to about 8 Ohms. As such the voltage
drop across the contacts is such that the Lights no longer
come on.
What a Fix involves:
While some have put a .22 Micro-Farad (uf) capacitor
across the switch wires, the only place to do it is under
the Instrument Panel (IP), and this reduces the efficiency
of the capacitor. The ultimate solution involves a $7
automotive relay from Radio Shack (275-226) which reduces
the current across the switch contacts to 0.16 Amps. As I
did this in conjunction with installing 50W Halogen backup
lights, I see this as the ultimate solution.
Replacing the switch (for shade tree mechanics):
As mentioned before getting to the switch is a bit of a
pain. You will have to jack up the drivers side of the car,
and put jack-stands under it. Unless you have very small
hands and are triple jointed, you will have to remove the
section of the muffler blocking your hand, and possibly the
2 nuts holding the clutch slave cylinder (requires a 13mm
LONG socket) to the bell housing. Use a 'seal pick'
screwdriver to raise up the tang on the weather-pack fitting
holding it onto the plastic switch housing and remove the
wires from the switch.
Al Kinder (USAZR1@aol.com) has built a special tool to
loosen the switch. If you wish to build your own, you will
require access to a machine shop and a welding facility,
otherwise borrow it from him). It consists of a 7/8" (22mm)
socket (normal length) that has been bored out at the socket
end to about .850" (big enough for the plastic to fit
through) and then welded to a 7" piece of 5/8" mild steel.
Assembled the tool has an L shape with the weld at the bored
out end of the socket. You will also need a 1 foot length of
steel pipe to use as a wrench 'extender'.
If you don't have the special tool, then remove the
muffler and go at the switch with a 7/8" box end wrench,
otherwise it should be sufficient to just remove the clutch
slave cylinder. Install the new switch, torque it up nice
and tight, replace the wires and anything else you removed,
and curse the design engineers who left you all that
clearance to get to it.
Installing a Capacitor or Relay:
To do this you will have to access the wires and
connectors under the passenger side of the Instrument panel
next to the Fuse box. You will need a 7mm socket and T-15
Torx socket to this. Open the fuse box panel cover and
remove it, use the Torx socket to remove the 3 screws
holding the fuse cover plate on. Switch to the 7mm socket
and remove the screw holding the plate hush panel. Look
inside the car and remove the other 2 screws holding the
hush panel. Undo the Velcro holding the carpeting to the car
and you now have access to the wires and connectors. Gently
squeeze the plastic hush panel to get it out. If you look up
at the connectors and wires, you will notice that some of
the connectors are loose, while others are connected via a
plastic prong to some un-named plastic sub-panel. It is two
of these that we are interested in.
One (black & gray) double connector (20 or 23 wires) has
a dark blue wire that carries the current from the 15A
backup switch fuse to the backup switch.
You can test this assumption (with a VOM) by removing the
fuse when the ignition is ON.
The other wire we are interested in is Light green that
is on a light blue 10 wire connector. This wire goes from
the (closed) backup switch to the lights.
Using quick connect wire splices (Calterm 61360)
available at you local automotive supply house, etc. you can
put a capacitor across the wires, or install a relay.
Relay installation is a bit more complicated, but anyone
with basic electrical knowledge should see that one has to
add a ground wire (look for the 2 screws holding a metal
plate below the fuse box), splice the Dark Blue wire to get
power, and split the Light green wire.
Depending on your skill, junk you have in your garage, a
solder-less connector kit, electrical tape or shrink wrap
tubing and some Black, Blue and light green wire along with
the appropriate tools will help speed the job along.
