4108 ignition - 4/5 terminals

[Wotname]

I don't suppose you have the electrical schematic drawing for the engine - they should tell everything about the existing wiring ???

[BigAl.NZ]

Originally Posted by Wotname

I don't suppose you have the electrical schematic drawing for the engine - they should tell everything about the existing wiring ???

Thanks for the replies. To get the photo I had to disconnect some wires - but they are all in use.

The original wiring diagram does show a ammeter and other things, so this was never wired quite to spec.

The spring loaded side of the original key hasn't got much spring left, so hence I was looking to replace.

Parts for engines sell a lot of Perkins parts and this is the ignition they suggest - so I have some confidence it will work, but this discussion has been good to get a slightly deeper understanding of how things should be.

[waterman46]

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?

If you have an external "smart" regulator, it supplies current to the field winding as soon as you apply battery voltage to the smart regulator. If using the alternator's internal regulator, residual magnetism in the rotor is enough to supply a starting current to the internal regulator.

[Cheechako]

The "Alt" doesn't feed the tach?

[Wotname]

Originally Posted by waterman46

If you have an external "smart" regulator, it supplies current to the field winding as soon as you apply battery voltage to the smart regulator. If using the alternator's internal regulator, residual magnetism in the rotor is enough to supply a starting current to the internal regulator.

A minor correction - not all alternator self excite, for some there is simply not enough residual magnetism for self excitation. Some of the internally regulated Hitachi models won't. They need an external source to supply the field voltage until they reach their "spin up' rotation. When this 'spin up' alternator rpm is reached, the alternator becomes self maintaining as the field voltage is now supplied internally by the field diodes off the stator windings.

FWIW, the 'spin up' rpm is usually lower than the idle alternator rpm.

Traditionally the initial field excitation is supplied through the CHARGE light. As the alternator output voltage rises, the CHARGE light now has ~12V on both sides of the lamps so it is extinguished.

[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?

The best way to know what to old switch does is to pull all the wire off and using your meter, map what is connected to what in all the switch positions.

Technically ACC should be the same as AUX but should be different to RUN.
RUN and ON should be the same however all switches are the same! Let your meter do the investigationS

[Wotname]

As smac999 says, most boats get by with a three position KEY switch - OFF, ON, START. All functions needed for the average boat diesel is achieved with such a switch.

However you will need four positions if you wish to include the HEAT function as part of the KEY switch.

[BruceS]

As an ex-owner in Australia I think it was 'acceptable' for sales/installs of this motor to not have a glow plug connected at all. Probably more common in very cold climates.
They don't have glow plugs at all but rather a heat activated item in the inlet manifold that opens to allow fuel to heat/burn at activation.
I had a separate heat activation button in the engine bay for the odd time I needed it.
Does the OP actually have the plug in the manifold?