Ignition switches, how they fail Options

[porschetub]

Had one fail in my 914,there seems to be a common failure point around the top casing that fits to the main assembly,this design is the the same for early Golf,944,T 1 and T2 aircooled Audi and I would expect many other in "the family''.
The return spring mounts via a tab on the spring into a hole in the top assembly,repeated use causes the area to crack.

The result is that the green plastic centre section loses tension and pops upward which in turn causes the metal wiper plate inside the switch to make a poor contact as it moves through its arc.

The end result of this poor contact is complete or partial failure,the crack in the housing shown in picture 2 is from my early 944 switch this was enough to stop injector pulse due to insuffient power to my ECU.
I pulled a known bad switch from another VW I had and found no crack in the housing but the contacts inside were all gummed up as the grease had gone bad and the contact pins were oxidized,cleaned it and it worked in the 944 till the correct replacement arrived.

[jim_hoyland]

Is it true that a remote hot-start relay takes the pressure off the stock switch and helps prevent the failures shown above ?

[Spoke]

Is it true that a remote hot-start relay takes the pressure off the stock switch

Yes. Every electrical component which is switched by the ignition switch requires electrical current. The ignition switch like any switch/contact has some finite resistance.

There are a couple of ways switching on/off electrical components wears out a switch:

1) Capacitive charging: We've probably all seen some arc when plugging in something to an AC outlet. An electrical component (relay, ignition coil, light, fan) all have some capacitance. When plugged in or ignition switch switched on, a very high current may flow when first connected to the point where an arc happens. This is not good for a switch and can prematurely cause failure.

2) In operation, a switch can get very hot from current flow. Every switch has some resistance. Current flow and resistance results in power dissipation (PD=I^2 x R) which results in temperature rise. High current = hot switch. Lower current = less hot switch. Heat over time may prematurely age plastic and physical stresses on plastic can cause the plastic to crack.

3) Inductive kick; When electrical components are turned off, inductance in wiring and the component try to keep the current flowing and can generate a large voltage and arc upon turn-off. The higher the current the higher the inductive kick. Again, not good for longevity of a switch.

and helps prevent the failures shown above ?

Not sure a hot-start relay can prevent the failure shown but it can help prolong the life of the switch. The ignition switch in many modern cars are nothing more than a push button switch with very little current flow. Other high current switches turn components on and off as well as the starter.

The 914 use of the ignition switch is crude by today's standards. Any extra relay's or SSRs that take away current from the ignition switch is a step in the right direction.

Think about the current loop of the bendix in a 914. Current flows from the battery to the front of the car to the ignition switch then back to the bendix to ground. That's a very long loop.

With a hot-start relay, the current loop for the bendix is from the battery to the starter through the hot-start relay on the starter. Very concise loop with heavy wires.