Whats wrong with our ignition switches?, What do we know? Options

[JeffBowlsby]

"Ignition switches are junk"

Regularly hear this and similar consternation.

I have continuously owned one or more 914s since 1998...think I have replaced only 1 ignition switches over that time, in one car. My current primary car I have had for over twenty years, still on the original switch as far as I know, I have not replaced it during my ownership.

None my cars have ever had the added relay although I'm not against it.

For those switches removed and in other key ignition switches I have opened up, what I see is part of the housing is cracked in similar locations. Maybe from years of torquing the key over? Not sure. I don't see melted housings (believe they are nylon), no smoke residue or anything out of line, just the cracked housing. Suspect the cracked housing causes some internal misalignment of the internal contacts...i.e. the switch goes bad and needs replacement.

I am thinking the problem is the switch housings that break, not anything to do with excessive current flow through the switch.

Educate me please.

[JeffBowlsby]

Without excessive current, then why the regular promotion of installing a relay? Does not seem to be necessary given the ampacity of the yellow wires involved. I never see the insulation on those wires cooked.

The main wire I see getting cooked is the black/purple tach wire on the ignition harnesses due to the mistake of reverse connecting to the coil with the black/red wire.

[ctc911ctc]

Just thinking outloud.... there is no current limiting circuits within any old analog cars. As a result if there is a manufacturing error or just sloppy percision, having a rotor that connects and then arcs can cause large instantaneous amounts of current. Not sure what the impulse current is on the Solinoid of the starter - this also can go out of spec and start drawing more current than designed.............. These small things, over time can erode the copper connections - dead spots etc.........



May have to think about this a bit -


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Without excessive current, then why the regular promotion of installing a relay? Does not seem to be necessary given the ampacity of the yellow wires involved. I never see the insulation on those wires cooked.

The main wire I see getting cooked is the black/purple tach wire on the ignition harnesses due to the mistake of reverse connecting to the coil with the black/red wire.

[Superhawk996]

Not sure what the impulse current is on the Solinoid of the starter - this also can go out of spec and start drawing more current than designed..............


May have to think about this a bit -

The OEM Bosch solenoid draws 25A. I’ve measured it on several starter solenoids using an accurate current shunt to make the measurement.



This goes back to the mythology. As circuits, wiring, and solenoids age, resistance increases, voltage drops increase. This decreases current draw.

Circuits don’t magically draw more current. Unless shorted and the smoke gets out but that is a whole different can of worms.

[bdstone914]

Not sure what the impulse current is on the Solinoid of the starter - this also can go out of spec and start drawing more current than designed..............


May have to think about this a bit -

The OEM Bosch solenoid draws 25A. I’ve measured it on several starter solenoids using an accurate current shunt to make the measurement.



This goes back to the mythology. As circuits, wiring, and solenoids age, resistance increases, voltage drops increase. This decreases current draw.

Circuits don’t magically draw more current. Unless shorted and the smoke gets out but that is a whole different can of worms.

If it draws 25 amps you don't tonk it needs a relay? I think most other parts like horns, fog lights, fuel pumps that draw less current are on relays. I dont think turning the switch harder causes the cracking. Is a weak design with a cast hole for the coil spring end leads to cracking. I once examined 10 used switches and 9 were cracked.
I believe in the relay.
I have not opened up any but I bet the contact get pitting that leads to excess heat and switch failure.
And most aftermarket switches seem to be junk.
I know someone who dropped a new one on the carpet of the car and it shattered.

[Superhawk996]

If it draws 25 amps you don't tonk it needs a relay? I think most other parts like horns, fog lights, fuel pumps that draw less current are on relays.

I dont think turning the switch harder causes the cracking.

On the first point - I don’t think it’s fair to judge vintage cars by modern standards.

Almost all cars of this vintage (both foreign and domestic) used high current switches for the starter and other things like headlamps, power windows, etc. The wiring and switch when new were sized appropriately to deal with the load. It’s the aging, voltage drops and the heat generated at high resistance junctions that are the root cause. I guess if we want to hold vintage cars to a modern standard we can say the high current switching is the root cause.

On the second point about turning the key harder I was being a smart ass. It is what people do but I agree with you that isn’t what leads to the ignition switch housing cranking that is very common. I do think it is part of what contributes to the center “key” portion getting wallowed out.

I’ve been around long enough to know that many people are still going to add the second relay. My main point is that it is unnecessary if the underlying system is sound (as designed) and that adding a second relay to control the first (ie the solenoid) is inelegant and is just another point of failure from a engineering Failure Mode Effects Analysis (FMEA) standpoint.

And on a side note about being stranded by a failure to crank. BS. You can slide under the tail end and use a screwdriver, a tire iron, or even spare change to short the solenoid terminal to the B+ terminal and the engine can be started. Not fun. But . . . I have been there, done that.

[GregAmy]

On the first point - I don’t think it’s fair to judge vintage cars by modern standards.

I agree.

But at the same time, I don't think it's fair to judge modern service and repair expectations by vintage design (unless you're shooting for Amelia center stage).

I stand by "it's your car, you should do with it what you want". But relaying a vintage starter solenoid when using a vintage starter switch is just good standard practice. And it's easy and cheap to do.

You can slide under the tail end and use a screwdriver, a tire iron, or even spare change to short the solenoid terminal to the B+ terminal and the engine can be started.

Ergo, your roadside repair is...relaying the solenoid.

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- GA