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"Multi-function" woes

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sd80mac7204

sd80mac7204

Jedi Warrior
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Had both low beam headlights fail on me Saturday night. After hours of trouble shooting it was discovered that the "multi-function column switch" had failed. A new one costs $500..."bad word"... Managed to find a reasonably priced new switch but it will take a week to get here. Looks like the Spitfire will be brought out of storage a bit premature...
 
Might be worth having a look inside the switch. On my Stag, the contacts were just metal rivets through a plastic arm. The contacts got a bit dirty, which caused them to heat up and melt the plastic arm. I was able to save the switch by gently heating the contact with my soldering gun, just until the plastic was soft enough to move the contact rivet back into it's correct location. I then cleaned the contacts and added a relay (so the original contacts only carry the relay coil current, about 80ma). Worked great (probably still would if I would get the engine rebuilt).
 
Anymore multifunction switches are just inputs to the Body contro module. Some are actually a small ECU linked to the main brain by serial bus cables. There's still contacts in there, but heat is not usually a factor anymore as the contacts only see milivolt signals and don't carry the current of the circuit like they used to. They're also a lot harder to take apart and inspect (I've done it) and are sometimes plastic-welded together, and can't be taken apart without breaking it.
At $500 I'm betting this one is of the ECU type.
 
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