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 ( 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.

Related Articles:

Jacking up the ZR-1. Scott Fabre

How to Jack-up a ZR-1. Michael Hom

Author: Steve Jasik

Posted in: Electrical
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