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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.
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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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914_teener
post Aug 12 2017, 04:38 PM
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Yep....

Very common. My switch failed when it got really hot and then the housing cracked exactly as shown.
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porschetub
post Aug 12 2017, 04:58 PM
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Part 2 of my rant (IMG:style_emoticons/default/av-943.gif) ,you can tell I had nothing else to do today (IMG:style_emoticons/default/rolleyes.gif) .
Two switches I pulled apart all had burnt centre contacts which is constant 12v,if the housing isn't cracked this appears to not happen as I found with the other VW switch.
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The real hassle is that until they fail completely which usually ends up with your starter grinding down your battery or nothing when you turn the key you just don't know ?.
Having read lots of posts on here and on the 944 forums about ignition/electrical and FI issues appear this little cheap nasty (design) part has a lot to answer for (IMG:style_emoticons/default/ar15.gif) (IMG:style_emoticons/default/ar15.gif) .
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porschetub
post Aug 12 2017, 05:00 PM
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QUOTE(914_teener @ Aug 13 2017, 10:38 AM) *

Yep....

Very common. My switch failed when it got really hot and then the housing cracked exactly as shown.


(IMG:style_emoticons/default/agree.gif) IMO more often the cause electrical problems that most know.
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ndfrigi
post Aug 12 2017, 05:25 PM
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same what happened with my previous 75.

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nditiz1
post Aug 12 2017, 05:46 PM
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So what is the fix?? I just bought a supposed "factory new OEM" switch off ebay today. Mine already has a push button starter installed as the PO was on his second switch. I am wondering if the broken switch I am still using (to turn the car on/off) is causing weird electric issues, mainly with the wiper blades working intermittently. Maybe I will install this new switch, but continue to use the push button starter. I don't really like the push button as it feels weird to stick the key in and turn it on but not go the last step.
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porschetub
post Aug 12 2017, 05:50 PM
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Hi Noel,that switch is a standard failure ,I really wonder how long the aftermarket replacements last,I see a genuine Porsche on some vendors sites which is way more expensive...is it better ,time will tell.
Maybe someone on here has bought that genuine switch ?....comments please.
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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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r_towle
post Aug 12 2017, 06:06 PM
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Thankfully, it's the same switch on mid to late 90-s vw cars.
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Mark Henry
post Aug 12 2017, 07:15 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 and helps prevent the failures shown above ?

Yep, see the link in my signature.

Just looking at those switches you can tell there was a fair bit of heat involved in their demise.
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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.

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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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jim_hoyland
post Aug 12 2017, 07:53 PM
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Thanks ! That is a terrific explanation. Can you elaborate on the use/need of a suppression diode on the hot start relay,,, (IMG:style_emoticons/default/smile.gif)

Tom had mentioned this in a threaf


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porschetub
post Aug 12 2017, 08:18 PM
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QUOTE(Mark Henry @ Aug 13 2017, 01:15 PM) *

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 and helps prevent the failures shown above ?

Yep, see the link in my signature.

Just looking at those switches you can tell there was a fair bit of heat involved in their demise.

Yep your starter relay fix is a good one,Mark out of 2 switches didn't really see any real heat,but mainly bad contact on the switch contact arm,funny got one from the 944 and stretched the 3 contact springs and it worked after previously being useless but its not a real fix for a sub $10 part.

One reply on here was wipers that didn't work anymore,thats the first thing that happened with mine then other stuff tipped over before total failure (IMG:style_emoticons/default/sad.gif) .
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porschetub
post Aug 12 2017, 08:46 PM
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QUOTE(r_towle @ Aug 13 2017, 12:06 PM) *

Thankfully, it's the same switch on mid to late 90-s vw cars.


I mentioned same design but not same switch,mounting points are different from model to model ,depends how they fit into the back of the ignition barrel.
The VW group later cars in many cases ditched this system for a more robust unit.....wonder why???.
A quick look on Pelican comes up with following;
meistersatz $8.25 ,have one in my car ok so far,
CRP $9 ,know little of this brand?,
genuine Porsche $40.50 ?.
That's why I asked if anyone had used the genuine one,honest think its a crap design can't see it making too much difference (IMG:style_emoticons/default/confused24.gif) .
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nditiz1
post Aug 12 2017, 09:11 PM
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Note that the genuine porsche one from PP does not include a 20% increase and 3-5 week ship from Germany. PP should really update the listing that they don't have the part and have to order it from Germany. I cancelled my order of that one for that reason.
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bbrock
post Aug 12 2017, 09:11 PM
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QUOTE(porschetub @ Aug 12 2017, 08:46 PM) *

That's why I asked if anyone had used the genuine one,honest think its a crap design can't see it making too much difference (IMG:style_emoticons/default/confused24.gif) .


Here is a recent thread discussing Porsche vs. aftermarket switches. http://914world.com/bbs2/index.php?showtopic=311314 Sounded like the expensive switch was the way to go. (IMG:style_emoticons/default/confused24.gif)
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porschetub
post Aug 12 2017, 11:52 PM
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QUOTE(nditiz1 @ Aug 13 2017, 03:11 PM) *

Note that the genuine porsche one from PP does not include a 20% increase and 3-5 week ship from Germany. PP should really update the listing that they don't have the part and have to order it from Germany. I cancelled my order of that one for that reason.

Sorry my bad,too many people buying the $8 part lol,pretty rude how PP do that considering they are moving boxes of stuff from Porsche on a regular basis.
bbrock that discussion never really came to a final outcome on the genuine switch,some having issues with the cheap ones however.
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r_towle
post Aug 13 2017, 12:33 AM
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Pretty sure they are all made in the same factory.
Brazil or Mexico
99 vw eurovan is the same, took me three switches to get a good one.
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Mark Henry
post Aug 13 2017, 07:22 AM
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QUOTE(r_towle @ Aug 13 2017, 02:33 AM) *

Pretty sure they are all made in the same factory.
Brazil or Mexico
99 vw eurovan is the same, took me three switches to get a good one.

I believe all the vanagons used this switch as well.
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Spoke
post Aug 13 2017, 07:57 AM
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QUOTE(jim_hoyland @ Aug 12 2017, 09:53 PM) *

Can you elaborate on the use/need of a suppression diode on the hot start relay,,, (IMG:style_emoticons/default/smile.gif)


The diode is sometimes referred to as a snubber since it prevents a large voltage from developing across a coil when the coil is turned off. The large voltage can damage transistors and cause switches to arc and shorten the switch life.

The diode snubs the inductive kick when the coil is turned off.

A coil is an inductor. An inductor stores energy in the form of current and resists changes in current. The voltage across an inductor is given by the following formula:

V = L x di/dt

where

L = coil inductance in Henrys
di = change in current in Amps
dt = change in time in Seconds

How large can the voltage across a coil get when turned off? Here's an example.

Suppose a switch opens up to turn a coil off like happens when starting the car and the starter is turned off.

Let:

Coil inductance L = 1H
Current I = 1Amp
Say the switch turns off in 1ms (0.001 sec); dt = 0.001 sec
Therefore the change in current: di = -1 Amp

Put these numbers in the inductance formula:

V = L x di/dt = 1H x -1A/0.001sec = -1000V

Attached Image

This is the inductive kick everyone refers to. Without the diode, the coil will kick back and may cause switch contacts to arc thus shortening it life. If controlled by a transistor, the high voltage may damage the transistor.

Placing the diode across the coil will give the current a path back to the inductor. The resistance in the coil, wiring, and diode will cause the current to decay to zero in a relatively short time.


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