4108 ignition - 4/5 terminals

[BigAl.NZ]

I am upgrading and tidying up the wiring on my Perkins 4.108.

Amongst other things I am replacing the ignition. On the existing Lucas 128SA ignition I counted 5 terminals and because some have two poles a total of 7 poles. The key has positions for OFF/RUN/HEAT/START.

I went to parts for engines and ordered what I thought would be right 4 terminals (6 poles) but of course this is 1 short!

https://www.parts4engines.com/perkin...nition-switch/

To make matters worse there was absolutely NO paperwork or wiring diagram included in the unnamed/branded box. Sigh.

What are the usual labels for each terminal of a 5 terminal ignition? If I look at https://www.autoelectricsupplies.co.uk/product/779 its almost like AUX/ALT (2 & 4) perform a similar function, but ALT is not on during HEAT or START?

Thanks.

[Wotname]

There are more than one set of labels for such switches however for the one shown in the link I would expect the terminals to work as follows.

Pin 1 is the same as position 1 i.e. OFF. This is where you would connect the battery (via fuses etc) to the switch.
Pin 2 is the same as position 2 i.e. RUN. This may or may be needed for a variety of circuits (alarm, charge lamp, possibly stop solenoid)
Pin 3 is the same as position 3 i.e HEAT thus goes to glow plug circuit
Pin 4 is the same as position 4 i.e. HEAT and START thus goes to start solenoid.

You should be able to confirm the above with a multimeter (continuity test).

[BigAl.NZ]

Originally Posted by Wotname

There are more than one set of labels for such switches however for the one shown in the link I would expect the terminals to work as follows.

Pin 1 is the same as position 1 i.e. OFF. This is where you would connect the battery (via fuses etc) to the switch.
Pin 2 is the same as position 2 i.e. RUN. This may or may be needed for a variety of circuits (alarm, charge lamp, possibly stop solenoid)
Pin 3 is the same as position 3 i.e HEAT thus goes to glow plug circuit
Pin 4 is the same as position 4 i.e. HEAT and START thus goes to start solenoid.

You should be able to confirm the above with a multimeter (continuity test).

But what is the 5th pin - ALT? What does ALT stand for?

Could I connect the ALT wire to AUX? since I now only have 4 terminals.

[Wotname]

ALT stands for alternator. Usually 12+ve comes from the switch (as soon as the switch is turned from OFF to the first position) and goes via a CHARGE light to the alternator. In an internally regulated alternator, it provides the initial excitation for the field until the alternator spins up and becomes self exciting. This is the process that causes the CHARGE light to initially illuminate and then to extingush once the alternator is producing an output voltage.

It is often called the IGNITION wire (IGN). It may also excite other circuits like the alarm lamps, gauges, buzzers and whatnot.

[Wotname]

Originally Posted by BigAl.NZ

.......
If I look at https://www.autoelectricsupplies.co.uk/product/779 its almost like AUX/ALT (2 & 4) perform a similar function, but ALT is not on during HEAT or START?

Thanks.

Sometimes the auxiliary circuits are de-powered while heating and starting - mainly because one can experience significant voltage drop while starting.

This protects the auxiliary circuits from such voltage drops. Depending on the loads etc, the terminal voltage of the battery might drop to 10 V and some circuits don't like this. It also prevents voltage spikes from affecting these circuits while starting.

It also removes additional current draw from the battery while heating/starting.

[waterman46]

The diagram of the 4 pin switch seems incorrect. Any ignition switch will have the following three basic positions at minimum: Off, RUN, START (spring loaded). The diagram is missing a RUN position. I suspect the "H" position is actually RUN and would be connected to your gauges and alternator.

Don't trust that diagram. Use a multimeter and figure out the terminals connected in each position of the key.


Depending on requirements of the 4108 for pre-heat or heat during cranking, you'll connect the heaters and starting solenoid to the HS and START terminals as required.

[BigAl.NZ]

Originally Posted by Wotname

ALT stands for alternator. Usually 12+ve comes from the switch (as soon as the switch is turned from OFF to the first position) and goes via a CHARGE light to the alternator. In an internally regulated alternator, it provides the initial excitation for the field until the alternator spins up and becomes self exciting. This is the process that causes the CHARGE light to initially illuminate and then to extingush once the alternator is producing an output voltage.

It is often called the IGNITION wire (IGN). It may also excite other circuits like the alarm lamps, gauges, buzzers and whatnot.

This comment you made about ALT = Alternator makes sense and I have that wire in my current setup going to the alternator for excitation.

Begs the question though - I see lots of other marine ignition switches out there - many, in fact most dont have a ALT pin - so what are they doing for there excitation?

[Wotname]

Originally Posted by waterman46

The diagram of the 4 pin switch seems incorrect. Any ignition switch will have the following three basic positions at minimum: Off, RUN, START (spring loaded). The diagram is missing a RUN position. I suspect the "H" position is actually RUN and would be connected to your gauges and alternator.

Don't trust that diagram. Use a multimeter and figure out the terminals connected in each position of the key.


Depending on requirements of the 4108 for pre-heat or heat during cranking, you'll connect the heaters and starting solenoid to the HS and START terminals as required.

I agree the wording of the description in the parts link is woefully inadequate however the "4 Pin" item (labeled as Fig. D.5.) is called an Earlier Heat/Start Switch. While there are 4 pins, there are only 3 connections on the switch. One connection is 12V input INPUT to the switch and the other two are outlets. One of the outlets goes to the start solenoid and the other to the heater circuit. This style of switch is typically used for older engines fitted with a generator.. Generator equiped older engines typically have no RUN function on the start switch. They were common on tractors back in the day.

The OP needs the "6 Pin" item (labelled as Fig D.1.), called a Current Heat/Start Switch. Although there are 6 pins, there are only 4 connections on the switch and each connection is designated with a number embossed on the plastic casing. The embossed numbers are 1 through to 4. I have referred to the embossed numbers back in my post upthread (post #2). Perhaps I have confused the OP by referring to the embossed numbers as pins rather than connections.

It becomes more confusing as different manufacturers used different ways of designating the various connections depending on the end use of the switches. The identical electrical connection may be labeled as ALT or IGN or ALT/AUX or 2 (in this instance) depending who made it for what use.

Suffice to say, I'm sure if the OP purchased the '6 Pin, current heat/start switch switch' and connected it as follows, it will work fine.
Embossed connection 1 to 12V +ve
Embossed connection 2 to Charge Lamp and other alarms (temp. oil press. et al)
Embossed connection 3 to glow plug circuit
Embossed connection 4 to start circuit

Disclaimers.
1. Confirm the switching actions with a multimeter (continuity tester)
2. I am not a Perkins 4108 guru so I am not sure how the STOP function is achieved on the OP's engine. If it is electrical and a function of the 'Ignition Switch' he may need more guidance.

[smac999]

Originally Posted by BigAl.NZ

This comment you made about ALT = Alternator makes sense and I have that wire in my current setup going to the alternator for excitation.

Begs the question though - I see lots of other marine ignition switches out there - many, in fact most dont have a ALT pin - so what are they doing for there excitation?

I don't see any reason to have a seperate pin for the alt. it would just come from the ignition / run pin.


cars have 4 places. off, acc (some stuff on, radio etc), ignition (everything on), start.

but I have never seen 4 on a boat. well some have a glow on they key, but then often start will be a 2nd button

[Wotname]

Originally Posted by BigAl.NZ

This comment you made about ALT = Alternator makes sense and I have that wire in my current setup going to the alternator for excitation.

Begs the question though - I see lots of other marine ignition switches out there - many, in fact most dont have a ALT pin - so what are they doing for there excitation?

It will just have another name e.g. IGN or ON or AUX or whatever.

IMO, these switches should all be called KEY switches rather than say Ignition switch or Start switch or On switch as such names are specific functions performed by the switch.

Typically a simple KEY switch has the following positions - OFF, ON, START (spring activated). It may also have HEAT and AUX. Obviously more functions require more connections (terminals/pins etc). Different manufacturers designated the connections as they see fit.

The alternator (initial) excitation is activated from the ON function. Some may call it ON, others RUN, others ALT etc but electrically it connects 12V+ve to the charge lamp as soon as the switch is turned ON.

Don't you luv circuitry

[BigAl.NZ]

Originally Posted by Wotname

Suffice to say, I'm sure if the OP purchased the '6 Pin, current heat/start switch switch' and connected it as follows, it will work fine.
Embossed connection 1 to 12V +ve
Embossed connection 2 to Charge Lamp and other alarms (temp. oil press. et al)
Embossed connection 3 to glow plug circuit
Embossed connection 4 to start circuit

Disclaimers.
1. Confirm the switching actions with a multimeter (continuity tester)
2. I am not a Perkins 4108 guru so I am not sure how the STOP function is achieved on the OP's engine. If it is electrical and a function of the 'Ignition Switch' he may need more guidance.

Where would the excitation wire go? ACC (2)?

[BigAl.NZ]

Originally Posted by Wotname

The OP needs the "6 Pin" item (labelled as Fig D.1.), called a Current Heat/Start Switch. Although there are 6 pins, there are only 4 connections on the switch and each connection is designated with a number embossed on the plastic casing. The embossed numbers are 1 through to 4. I have referred to the embossed numbers back in my post upthread (post #2). Perhaps I have confused the OP by referring to the embossed numbers as pins rather than connections.

My original ignition (Lucas128SA) has 7 pins (5 terminals or connections as you called it). See picture.

The 5th pin is the ALT pin. So the "6 pin" item is not a exact replacement as its missing the pin for ALT - but it wounds like ALT can be connected to ACC or RUN or AUX - all names for the same thing?

[Wotname]

Originally Posted by BigAl.NZ

My original ignition (Lucas128SA) has 7 pins (5 terminals or connections as you called it). See picture.

The 5th pin is the ALT pin. So the "6 pin" item is not a exact replacement as its missing the pin for ALT - but it wounds like ALT can be connected to ACC or RUN or AUX - all names for the same thing?

Hmm... All I see are 5 numbers embossed into the switch housing so where is the ALT descriptor located.

I am not carnally familiar with the Lucas 128SA but the best way to know what is what is to check (with a meter) what terminals are connected to which other terminals as the switch is tuned though the various stages.

How many positions has the Lucas switch got and what are they called?

[Wotname]

Opps, I see you mentioned the positions and names in your OP - sorry!

Are both the HEAT and START spring loaded or only the START?

[Wotname]

It also seems you are only using three wires on the Lucas switch. Best guess from afar that one is the input and there other two are the ON and START functions.

Everything apart from the START wire goes to the ON position.

Does the engine have glow plugs and are they activated by a seperate switch?