Dino Saga 071103 _ Ignition Switch, 2007

Dino Saga 071103 _ Ignition Switch, 2007

Way back in 2005 I posted a Saga that talked about the few Dino electrical items that caused problems up to then. The ignition switch acted up at 55,000 miles. Problem was intermittent starter operation. Would often take two or three tries with the key to get the starter to kick in. Replaced switch, all OK, but problem started again at 80,000 miles. Decided to find the cause rather than just keep replacing the switch.

The electrical part of the switch is made by Bosch and was used on many high end cars. Mercedes, BMW, etc. The Bosch assembly comes off the lock with two slotted screws. The switch has a bakelite body and a separate rotor assembly attached by the two hollow rivets. I unrolled the ends of the rivets and carefully took the switch apart. Lots of pieces inside including springs and balls. There are 4 single contacts and one double contact staked into the bakelite body. The starter contact had been burned almost away. I found that I could unstake the contact and remove it. I brazed material back onto the tail of the contact and filed it to the original shape. Staked it back in, assembled the switch and all worked fine on the bench.

Went out to the car, shifted to neutral and jumped the white starter wire to the red battery wire. The starter turned and when I unjumped the wires there was a beautiful arc. I am a retired electronic engineer and have worked with relays of all sizes and types. You learn early about the kick you get when you open the coil of a relay. We always put diodes across DC relays to protect the device that is doing the switching. The starter solenoid is a monster relay, lots of inductance in the coil and a few amps going through it. There was the problem. Solution was trivial. Add a diode.

I used a 1N4004 silicon diode in a plastic case. Rated for 30 amps surge, 1 amp continuous, 400 volts. The 1N4000 series is found everywhere. Any last digit is OK since 14 volts is as high as the voltage is likely to get. Anything of 1 to 3 amp continuous rating is big enough. The only time it works is for the few milliseconds after the start switch is opened. Without the diode, the voltage can go to thousands of volts and create a beautiful arc. With the diode, the voltage stays at battery voltage and the diode absorbs all the energy stored in the solenoid coil. Radio Shack or any other electronic parts dealer has something that will work.

3-6 inches of flexible wire on the diode ends makes later service easier. My car has the white starter wire and a smaller brown wire crimped into the female switch connector. The brown wire is more flexible and easier to connect to. White band (cathode end) of the diode goes to the brown wire. Other end of diode goes to ground. Fix has been good for more than 100,000 miles and God knows how many starts. Lots of Dinos getting on in miles now and the starts add up. Switch will fail eventually. Folks are starting to ask.

Took a shot of the keys. I am on my second ignition copy. Mercedes blank. I cut off funny ear. About time to do it again. Not too hard to keep things going. Drive.

John
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