Hi: In rewiring my 12v system on my car to an aftermarket fuse+relay panel, I found that my foglight and rear defrosters didn't work. The wiring was in place correctly because (in the case of the foglights) connecting the two wires (pink and pink w/ black) caused my fogs to turn on. When I started disassembling the buttons, it occured to me that there is really NO reason to make these switches so complicated. Near as I can figure it, the only reason to have these push button switches be a rectifier flip-flop based circuit triggering a relay instead of a simple mechanical switch is that the designers wanted the button to "feel" the same when activating vs deactivating. If you think back to other push button switches that have existed for decades (like on a PC case), a mechanical spring mechanism is what latches and unlatches the two wires. Grumbling aside, I set about replacing the ONE item which could conceivably break since the car was assembled in 1982 -- the old capacitor in the switch. 1) Gently remove the black plastic border around the button by pulling it forward (its held with tension on 4 plastic protrusions) 2) Put the button/spring, small metal contact plate underneath the switch, and the button surround in a ziploc bag. Image Unavailable, Please Login 3) Drill out the rivets; save the mounting tabs into the same plastic bag. When drilling out the rivets, I used a 1/8" drill bit and the goal was to remove the rivet head. If you drill out too much you COULD potentially damage the contact on the PCB. Unlike other designs, the electrical point of contact is on the surface of the PCB vs a sleeve going through the 2mm hole. You DON'T want to accidentally grind off the PCB's contact. Image Unavailable, Please Login 4) Gently push out the guts of the switch by pressing the two plastic tabs holding it on the side. You'll see it come out as 2 PCBs mounted at 90 degrees to each other withone holding the surface that the button pushes against and the old holding a relay and the cap. In this pic you can see one of the two solder points on the PCB desoldered already Image Unavailable, Please Login 5) Desolder the 25v 22uF cap (2 solder points on the bottom PCB) Image Unavailable, Please Login 6) Replace the cap with a new one. Pay attention to the direction the cap was installed (the negative leg was connected to the hole PCB closest to the edge). To be safe, sleeve the new cap with heatshrink tubing (I just reused the old one) so it doesn't inadvertantly short on the relay NOTE: If you are thinking about it, now is a good time to replace the green LED with a much newer, brighter one in the color of your choice. You will want to make sure you install it in the right direction and test the voltage but I'm willing to bet its a 12V LED. 7) Reassemble the guts into the case. 8) To install the rivets: - Buy some 2mm HOLLOW rivets: https://www.amazon.com/dp/B07RDKN5DP - place the rivet underneath the PCB and stack the metal tab on top (a small piece of tape to hold both in place helps) - Be sure to support the PCB so when you whack the top you are not flexing the PCB. - Use a small roll pin punch to spread open the rivet hole from the top. The tip of the roll pin punches have a small bearing that centers the punch on the river and spreads out the tube. Once a "head" is formed to hold the metal tab to the top of the PCB, a larger roll pin can whack the rivet to be more secure. I stopped when the tab wouldn't wobble and was securely attached to the PCB. Image Unavailable, Please Login https://www.amazon.com/Pieces-Gunsmithing-Removing-Automotive-Jewelry/dp/B07JNS1ZF7/ 8) Reassemble and reinstall in your dash (or test it) Image Unavailable, Please Login For both the foglight and the rear defroster, the two space connectors in the middle were the ones that the switch connects/disconnects. The ones on the edge are 12V and ground for illumination. IIRC, there's a 5th wire on the rear window defroster button; I'll bet that is for an indicator light. Total cost for me was a few bucks for the new rivets as I had everything else already.
Another tidbit: You'll notice that I didn't find a cap that exactly matched the specs of the original NOR did I find one in the same shape. - Shape didn't matter as all you need to do is make sure you can get the legs into the right holes. - Capacitance matters (the microfarad rating) but the voltage rating on a capacitor is the maximum safe voltage the cap is rated for. You typically size a cap for 2x the max rating so if this was a 12V switch, 25V is safe and 63V is overkill. Here's an assortment for $10. https://www.amazon.com/EEEEE-0-1uF%EF%BC%8D2200uF-capacitors-Individual-Electrolytic/dp/B08V5815K7
Don't disagree that it is overly-complicated and super-fragile, but the reason for it being a self-latching relay is so that it can't be left "on" when the key is turned "off". I.e., once the key has been "off", you have to push the button again to turn it back "on". If it was just a simple mechanical on-off switch fed by a relay that was only actuated with the key "on", if you left the mechanical switch "on" and went to start the car = the device controlled by the mechanical switch would be drawing current while trying to start the engine.
Huh. You make a good point, Steve. I imagine this was a much bigger issue back in the 80s with both the rear window defroster AND foglights which were halogens. As another thought - perhaps wiring the car so that these buttons only get current when ignition is on (vs circuits which are always hot) could have been an alternative way to solve the issue; that's how I setup these circuits when I replaced my fuse+relay panel. Clearly Mario/Luigi/the engineer who designed this system had a different ideas. Also, on 2022, its not hard to replace the fogs with LEDs. Mine turned out pretty well; I just removed the reflector and installed these light bars (this QV car came with a Mondial 3.2 front bumper). https://www.amazon.com/gp/product/B07ZJHL2Z
No, this doesn't work because the ignition is "on" during engine starting (so the device would be "on" during starting if the mechanical switch was left "on"). My biggest complaint with these switches is their terrible tactile feedback and very small motion of the pushbutton -- it's so hard to "feel" anything when trying to actuate them. Your point about this being less of an issue if the device current can be reduced (i.e., using LED) is valid, but they weren't available then, and the rear window heater is always going to use a fairly large current.
Gunn it's a legal requirement that the fog lights turn off once you turn the ignition off so you don't drive off the next day with your fog light on when not needed, because in most European countries it's illegal to use fog lamps unless there is fog. From the front it's a dazzling/masking of indicator question, from the rear it's mostly a question of distinction/masking of the stop light. This problem is somewhat resolved since the adoption of the third stop light. So the the fog light switches need to wired in a way they turn off once the ignition is turned off. For the heated rear window it's a question of power consumption. Gas isn't as cheap in Europe as in the US so the manufacturers do everything they can to reduce energy consumption when not needed. Hence the heated rear windows will turn off automatically with ignition off. Your "mechanical" solution doesn't address these requirements so they weren't a solution for Ferrari.
