This past weekend my Switch pack module failed on my 2005 Elise.
I searched around and did not see any good write up on how to repair the unit.
First off my problem. When i switched on the headlights, the parking lights would not come on. The switch on the dash did nothing, and the center indicator in the switch would not light.
So the first thing I did was to try to isolate the problem. Since the Headlight and the parking light switches are the same I removed the lighting panel (There are two screws in the cubby hole below the lighting panel). Then I unplugged both the headlight and the parking light switch. then I plugged the parking light switch in the headlight connector, and the headlights could switched on and off with the parking light switch. So I knew that it was good.
The next step is a bit harder. to get at the switch pack module you have pretty much disassemble the dash.
Disconnect the battery before you do anything else!
Here is a good write up on how to remove the dash:
With the dash top removed, the Switch Pack Module is right behind the instrument cluster. I had to remove the instrument cluster to get at the two screws that hold it in place.
Now with the Switch Pack Module loose there are two connectors one shorter and one longer, both have a tab on them, push the tab down and pull on the connector, they should come right out.
Here is a picture of the Switch Pack Module (Not my module. My Module is # C117M0008F):
On the case there are four tabs, you can gently pry them up, and separate the two halves of the case.
Once opened, you will see the board. There are a number of relays on the board. Using the wiring diagram from Lotus and a multi-meter, I traced the relays down to their function.
I have labeled them in this image:
I suspected the relay (part number HG 4117/02 SH1S) may be the problem, I so I looked it up and found the spec sheet for it.
Relay Data Sheet
Here is a electrical diagram for the relay:
This relay is what is called a double pole single throw, which means that both sets of contacts are on at the same time. Lotus has wired both contacts in parallel to handle the current load of the lights.
I found that in my case the parking light relay's coil was open (> 300 Ohms). The other relays measured about 130 ohms across the coil. So now I knew what was broke, next was to fix this problem. Since I don't have rear fog lights (And most in the US don't either) I unsoldered that relay, and used it to replace the parking light relay.
I left the fog light relay pads empty, in case I ever order some replacement parts, I can fix it easier later.
Hope this helps some folks.