How does the starter switch circuit work + more questions

[steckmeyer]

First, I will confess that I'm am not a trained DC circuit technician so if my questions are answered with an understanding of the superb schematic available on this forum I apologize.

1. How does pushing the started button (closing the circuit) increase the primary voltage to the ignition? I see two contacts going from the ignition switch to the starter switch and one going from the starter switch to the starter, nothing else.

2. Can the starter switch be disassembled and cleaned? Can Wurth contact cleaned just be sprayed into the switch and will that clean the contacts?

3. The ignition switch has five wire connectors. All are numbered but some have an additional (a) with the number. What does this signify? Is this a single pole switch or is it completing multiple circuits? If it is completing multiple circuits how are they identified?

4. Can the ignition switch be disassembled and cleaned? Are there any photos of this switch disassembled?

Thank you for your help.

[GRCameron]

The switch body is crimped to the base, so it can't be disassembled. Getting contact cleaner into the switch would be difficult because it is sealed from moisture.

Here's a wild guess as to what is going on with the ignition switch and starter button. It may be way off since I haven't examined an ignition switch for continuity on the 'off' and 'on' positions.

1. When the ignition switch is moved to the 'on' position using the key, 24v is available at terminal 16a which goes to the starter push-button. Terminals 61a and 16 are connected together.

2. When the starter push-button is pushed two output terminals are energized, one going to the starter solenoid and the other going to the end of the ballast resistor that also connects to the coil through the suppressor. When the button is pushed, full bus voltage is applied to the coil. Under normal running conditions the 4500 RPM module supplies coil voltage to the coil through the ballast resistor.

A guess, as I've indicated. Someone who's delved into the wiring further than me may have a better explanation.

Item 25 is ignition (key) switch
Item 31 is starter push-button
Item 41 is ballast resistor
Item 61 is 4500 RPM module

[pcolette]

I think that George is correct in his explanation. The ignition switch does complete multiple circuits since it also provides power to the various circuit breakers. It may be possible to dis-assemble it though I tried once and just made things worse.
The starter button has been known to fail over time. I've tried cleaning with contact cleaner with moderate success.

Can you describe the problems you are encountering? Maybe someone will have some ideas for you.

[steckmeyer]

A week ago while driving my 710K the engine just stopped. I was exiting the Interstate and while slowing down on the exit ramp the engine cut out. It was raining and I had been going around 60-65 mph for 25 minutes. When this happened I was in traffic and did not observe everything as well as I should have. In order to get out of the way I ran the truck onto the berm with the starter. I tried to start the engine several times without so much as a burp. I don't remember if I cycled the ignition switch more than once but after a few tries (and after I did cycle the ignition switch) she started right up and ran fine for several hours including stops, starts and shut downs.

My worst fear is an intermittent electrical problem. I suspect the primary ignition circuit. I plan on tracing it back from the distributor to it's origins (where ever that is) looking for loose connections, frayed wires, ground faults, loose or dirty terminals and so on. Before I start I want to understand as much as I can about the schematic. The starter switch wiring does not make sense to me.

The PO has suggested to me that my problem may be the ignition switch. Since the ignition switch costs $250 and I suspect electromechanical devices on principle I want to know as much as possible about it and any options I might have.

Thanks again for considering my problem

[pcolette]

Okay, based on what you've described my first thought is that possibly your coil overheated and quit working. I've read other threads on here about that happening and have had it happen to me but I don't know if a coil can recover from it after cooling off. I replaced my coil after my occurrence and didn't have the problem again.
The ignition switch is quite robust and I would be less inclined to suspect it but anything can happen on vehicles this old.

[David Dunn]

To answer Paul, the coil will recover, but are weaken. The common reasons for coils to overheat are the ballast resistor is removed or bypassed delivering full voltage to the coil all the time. The other cause is a bad regulator or alternator delivering way too much voltage ( voltage needs to be checked at highway RPMs). This is also a major killer of Pertronix units (they DON"T recover). Max voltage should be 28 to 29 volts ( if my mind serves me right )

[Jimm391730]

I have had my ignition switch (key switch) not make full contact with all terminals; in my case, pushing the starter button cranked the engine and energized the coil so the engine would catch; but when the starter button was released the engine just died. The ignition switch had not made proper contact to energize the coil/ballast resistor/RPM module to keep the spark alive when the starter button was released. Once or twice a year, this happens again and I just have to wiggle the key switch to get all the contacts to connect properly. It doesn't happen enough that I've worried about it but it might be that you are seeing the same occurrence.

[landais]

Ignition switch(25) provide two set of contacts.When key is turn "on",the 28v from battery connected to the terminal 30 is provide to the terminal 15 and terminal 61a. Also at the same time a separate contact is made between terminal 16 and terminal 16a.
Upon pushing the starter button the 28v coming from the terminal 61a is connected to the starter relay ( motor) and to the terminal 16 that in turn is connected to 16a .
Terminal 16a is connected to the ballast resistor at the level off the coil/ballast.These 2 are in series.
Therefore the ballast resistor that normally receive the voltage through the 4500 rpm module is by-passed and the coil receive 28v. When the starter button is removed,no more 28v at coil/ballast connection and now the ballast is in series with the coil and 4500rpm module. The 4500rpm module has two function:
-monitor the rpm of the motor ,reduce voltage if exceeded
-provide voltage to the ballast ans coil.
It can be removed but a connection between the 2 central terminals need to be made to provide a 28v to the Ballast and coil.
alain

[landais]

Read terminal 16 is connected to coil/ballast and 16a to starter button..

[steckmeyer]

Excellent explanation. Thank you.

[steckmeyer]

After thinking about this for a while I have two questions:

Why is it necessary to break the 28 volt supply to the coil inside the ignition switch (terminals 16 & 16a)? Couldn't you achieve the same isolation if you just hooked terminal 16 to the motor side of the starter switch? What am I missing?

Is there any reason that in a pinch you could not replace the ignition switch with a $10 DPST 6-36 volt 25 amp (@12v) toggle switch?

[landais]

The ignition switch can be replace by a single SPST that will connect +28v (Term.30) to Term.15 and Term.61a ( Term61a and Term 15 wired together).
Ignition switch has 2 Term. 30 and 2 Term. 15. and there is a lot of connection there...
Term. 16 should be OPEN after motor running to have the resistor ballast in series with the coil, reducing the voltage at the coil level. The 4500rpm module provide the +28v to the Ballast and coil.
Starter switch can be replaced by a DPST with momentary connection,one connection between Term.61a and motor,the other between Term.61a and the wire going from Term.16 to ballast coil connection.

[JNijst]

Gentlemen,

I am in the 'planning stage' of installing Jake Raby's EFI and need to analyze the electrical circuit and came upon this excellent explanation of the ignition-switch and starter-button. I added this 'simplified' drawing of the circuit, it shows the starter-button as in real life; no connection to any voltage until pressed.
However I cannot figure out why the original Pinz design team ever included this strange 16 and 16A connection, you could connect these two permanently; because:

- No voltage ever flows to 16A and 16, unless the starter-button is pressed (so no voltage (28V) bypasses the resistor)
- Upon starting: voltage flows from 61A through the button to 16A and 16 and bypasses the resistor(41) - straight to the suppressor.
- After running the engine: no voltage flows from 16 to the Suppressor(40) so no voltage is bypassing the resistor(41), because the starter-button is released

I am sure I am missing something, but don't know what. The only reason the team included the 16-16A connection, would have to do with: after you switch off the ignition and accidentally pressed the starter-button or something,
Can someone shed a light for me ?

Thanks and best regards

Jules

[Jimm391730]

I agree with your analysis; 16/16A are not needed (they could be connected permanently). The only reason that might make sense as to why it is there is if it was originally expected to use a "standard" key switch with a cranking position instead of the separate cranking button. When someone decided to add the button, the starting position sections of the key switch were eliminated but they missed removing the ballast resistor bypass contacts. But that's just a guess.

I'm not familiar with Raby's EFI, but most EFI computers include ignition as well (at least the Motec and EMS system that I have do) and in my case the ballast resistor and button contact are no longer used. Modern ignitions are so effective that they don't need to have a change of voltage during stating. For my system, the key switch supplies power to the EMS (through the 24 to 12V converter) and when the EMS computer senses rotation, it injects fuel and times the spark. The button is only energizing the starter.

[JNijst]

Hi Jim M

I was just asking in case I missed something. I am planning to use a simple lockable ignition switch instead of this expensive original switch.

You're right; for the EFI a different coil is part of the kit and it does not mention anything about ballast-resistors, just turning the start-motor should start the whole system, but for that you would need a hefty (30 amp ?) switch, or a relay that you could energize with a cheap, but neat looking, start-button. I always liked the look of the start-button...

Anyway thanks for the reply.

Best regards,

Jules