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> Ignition switches, how they fail
porschetub
post Aug 12 2017, 04:25 PM
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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.
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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.
Attached Image
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.

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jim_hoyland
post Aug 12 2017, 05:59 PM
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Is it true that a remote hot-start relay takes the pressure off the stock switch and helps prevent the failures shown above ?

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Spoke
post Aug 12 2017, 07:23 PM
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QUOTE(jim_hoyland @ Aug 12 2017, 07:59 PM) *

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.

QUOTE

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.
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Posts in this topic
porschetub   Ignition switches   Aug 12 2017, 04:25 PM
914_teener   Yep.... Very common. My switch failed when it got...   Aug 12 2017, 04:38 PM
porschetub   Yep.... Very common. My switch failed when it go...   Aug 12 2017, 05:00 PM
porschetub   Part 2 of my rant :rotfl: ,you can tell I had not...   Aug 12 2017, 04:58 PM
ndfrigi   same what happened with my previous 75.   Aug 12 2017, 05:25 PM
nditiz1   So what is the fix?? I just bought a supposed ...   Aug 12 2017, 05:46 PM
porschetub   Hi Noel,that switch is a standard failure ,I reall...   Aug 12 2017, 05:50 PM
jim_hoyland   Is it true that a remote hot-start relay takes the...   Aug 12 2017, 05:59 PM
Mark Henry   Is it true that a remote hot-start relay takes th...   Aug 12 2017, 07:15 PM
porschetub   Is it true that a remote hot-start relay takes t...   Aug 12 2017, 08:18 PM
Spoke   Is it true that a remote hot-start relay takes th...   Aug 12 2017, 07:23 PM
r_towle   Thankfully, it's the same switch on mid to lat...   Aug 12 2017, 06:06 PM
porschetub   Thankfully, it's the same switch on mid to la...   Aug 12 2017, 08:46 PM
bbrock   That's why I asked if anyone had used the gen...   Aug 12 2017, 09:11 PM
jim_hoyland   Thanks ! That is a terrific explanation. Can y...   Aug 12 2017, 07:53 PM
Spoke   Can you elaborate on the use/need of a suppressio...   Aug 13 2017, 07:57 AM
nditiz1   Note that the genuine porsche one from PP does not...   Aug 12 2017, 09:11 PM
porschetub   Note that the genuine porsche one from PP does no...   Aug 12 2017, 11:52 PM
r_towle   Pretty sure they are all made in the same factory....   Aug 13 2017, 12:33 AM
Mark Henry   Pretty sure they are all made in the same factory...   Aug 13 2017, 07:22 AM
McMark   As 3D printing has evolved I've wondered if so...   Aug 13 2017, 08:24 AM
Mark Henry   As 3D printing has evolved I've wondered if s...   Aug 13 2017, 11:30 AM
rhodyguy   Anyone with first hand experience on the German on...   Aug 13 2017, 11:37 AM
mepstein   Anyone with first hand experience on the German o...   Aug 13 2017, 12:10 PM
Porschef   Anyone with first hand experience on the German o...   Aug 13 2017, 01:12 PM
porschetub   [quote name='rhodyguy' post='2516510' date='Aug 1...   Aug 13 2017, 06:23 PM
Mark Henry   [quote name='rhodyguy' post='2516510' date='Aug ...   Aug 13 2017, 06:48 PM
barefoot   [quote name='rhodyguy' post='2516510' date='Aug 1...   Aug 14 2017, 11:35 AM
Jeff Bowlsby   Porsche OEM only, the cheap knockoffs do not last....   Aug 13 2017, 04:18 PM
porschetub   Yea have seen that metal switch Mark ,got to be be...   Aug 13 2017, 06:08 PM
nditiz1   I did call the local dealership, but the guy on th...   Aug 13 2017, 06:16 PM
mepstein   I did call the local dealership, but the guy on t...   Aug 13 2017, 06:23 PM
Mark Henry   111-905-865 L Type one 1974 to 1998, I assume the...   Aug 13 2017, 06:57 PM
Porschef   I don't know what the part numbers are, all I ...   Aug 14 2017, 03:50 AM
saigon71   Thanks for the info on the "Genuine Porsche...   Aug 14 2017, 05:39 AM
nditiz1   Does anyone know if the part number above will wor...   Aug 14 2017, 06:02 AM
michael7810   Does anyone know if the part number above will wo...   Aug 14 2017, 07:16 AM
nditiz1   Coming from aircooled beetles I am wondering how t...   Aug 14 2017, 08:22 AM


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