Evening all, does anyone know why someone would solder a diode in between the two wires that engage the starter selanoid ? I've just found one fitted to my 998 whilst tidying the wiring up and not sure why it was ever fitted. It has had an alarm/imobilzer fitted and removed at some time.
When you release the key and the power to the solenoid is turned off, the movement of the magnet inside the coil in the solenoid induces a reverse current (basically the opposite of operating the solenoid ie; motor vs generator), this can sometimes be high enough to fry the wires, the diode allows this current to pass harmlessly to earth.
Cheers guys, I can understand why a 999/749 would have one because they have a more complicated set up but my 998 has the simple push button which breaks the circuit when you release the button so any returning voltage shouldn't be able to go anywhere really ? But if its a std fit I best solder it back in then !
The voltage that can be induced will be thousands of volts (low current though), this can be enough to arc across the gap between the contacts in the push button allowing a circuit to form.
It's function is to protect the ECU from big negative voltages when the solenoid switches off and the field on the windings collapse
Diode supress voltage/current spikes from starter solenoid. Striped part on diode should be oriented towards + cable, black body towards -. However the one used seems to me to be on the verge of being underrated (as it is in DO41 package ?). Better equivalent would be P600M or 6A60. They are cheap, 20 pence/unit and can be bought from ebay/mouser for £1.50 in package of 10. if it says 1n4001,1n4004 or 1n4007 on package, get rid of it, as it may easily fail. The better (by order of magnitude) is to use transils. They look like diodes, but are vastly superior.
