1992 Wiring Diagram Puzzle?

[ColinJB]

Dear fellow boaters perhaps someone can help me here.

1992 vintage boat.  BMC 1.5l Diesel.  I am 4th owner.

Control panel wiring best described as "rats-nest".  I am lucky (?) enough to have the original wiring diagram.

I am attaching that drawing.  I've blanked out company name that did this install as they don't exist anymore.

What is puzzling me is the "Warning Light" section / symbols.  I suspect this symbol combines both the incandescent bulbs and relays?  There are two fairly standard 5pin SPDT automotive relays in there.  Various colour wires and various crimps to other colour wires.  This is not the standard symbol for a relay coil, switches  and common.  Surely a bulb is just a bit of wire in a glass bottle?

I have none of the optional items detailed on drawing.

Really hope someone out there can help identify the 3 connections on each box on the drawing.  How do they map to the pair of standard relay terminals?  Are all 10 relay terminals used?

Everything else sort of makes sense even though been added to over the years.

Many thanks in advance.

[Jen-in-Wellies]

Welcome to the forum.

The wiring on all older boats ends up as a rats nest, with repairs and additions made by assorted owners and boat yard electricians of varying skill levels. Yours is probably one of the neater ones!

Whatever the relays are doing, they are nothing to do with the bulbs and are a subsequent addition, if you can't find the in the other diagrams. The builder hasn't used standard electrical symbols here, but representations of the actual parts themselves, so the four warning light symbols probably represent the holders the bulbs push in to. All four bulb holder connections make sense. The glow plug one activated along with the glow plug from position 3 of the key switch, with the other side going to ground. The starter motor solonoid activated from position 4 and the alternator, oil pressure and water temperature warning lights, plus the instruments activated from position 2. My guess is that there are two connections to one side of each bulb on the holder and a single connection to the other side. A way of joining wires that are both going to one side of a bulb.

See if one of the coil connections for the relays (pins 85, or 86) can be traced back to position 2 of the key switch. This would switch in some higher current loads when the engine is going.

[Tony Brooks]

There is no reason for relays for the oil pressure, alternator, and overheat warning lamp (you say you don't have the optional overheat warning lamp).

 

A relay might be used in the glow plug circuit, but certainly NOT on/under the control panel.

 

I think they are trying to show they are using the lamps as junction boxes, so they loop (say) the live feed to the next lamp. So think of it as each lamp having thee terminals, with one air of terminals being joined at the lamp - I bet rather than three terminals you have two terminals and a piggyback.

 

Why they did not use a conventional symbol or pictogram for the lights, I have no idea.

 

Edited to add:

 

I think this diagram from my website may clarify it.

 

 

 

Note - F on the alternator is the warning lamp terminal, D+

Edited June 11 by Tony Brooks

[ColinJB]

Many thanks for all your interest here.

That word "Piggy back" may be a clue.  There are various piggy back spade terminals in there!  Both on lamps and ignition switch.  Perhaps capacitor like symbol means piggy back to one side of the bulb with two or more wires?

A bit of context here.  The original ignition switch was sloppy / knackered so I replaced it with identical "new old stock" Lucas 4 way switch.  In the process of doing this, I must of disturbed the rats nest.

To be honest, I've never really understood what 2 of the 3 lights are telling me?  Red lamps OIL and IGN (Battery Logo) in diagram.  When should they be on or not on?  All VDO sensors are new.

From older Diesel cars, I would expect the Orange Lamp to be on while warming glow plugs (Pos #3 on switch).  Then fire Pos #4. Orange goes off once engine started, perhaps triggered by field coil signal from alternator via relay?  A "NOT" state from relay?  Spring return key to Pos #2.

For the moment, I have decided that POS #2 on switch just delivers current to "Bells, Lamps and Whistles".  All removed and insulated for now.  I can start the boat using just POS #1,3,4.

Originally a load of stuff connected to POS #2 on switch with piggy back terminals!

Very close to rip it up and start again ;-(

[Jen-in-Wellies]

10 minutes ago, ColinJB said:

Perhaps capacitor like symbol means piggy back to one side of the bulb with two or more wires?

Very likely.

10 minutes ago, ColinJB said:

Red lamps OIL and IGN (Battery Logo) in diagram.  When should they be on or not on?

Red lamp goes to a pressure switch on the engine. When the engine is off, or the oil pressure has died, then the pressure switch closes, allowing current to flow from the ignition switched live, through the lamp and through the switch to the engine block, which should be connected to the battery negative. When the engine oil pressure builds, the switch opens, the lamp goes off. When the switch is at position1, off, there is no 12V to the circuit and the lamp is off.

IGN connects ignition switched 12V to the bulb to the W connection of the alternator. When the engine is stopped, or the alternator is not working, then there is current flowing through the bulb to the alternator and the bulb lights. When the alternator starts charging, the W connector rises to 12V and no current flows through the bulb and the bulb goes out.

10 minutes ago, ColinJB said:

From older Diesel cars, I would expect the Orange Lamp to be on while warming glow plugs (Pos #3 on switch).  Then fire Pos #4. Orange goes off once engine started, perhaps triggered by field coil signal from alternator via relay?  A "NOT" state from relay?  Spring return key to Pos #2.

Spring returns to position 2 when the key is released, which automatically disconnects the glow plugs and starter motor, as these are only energised when the key is in positions 3 and 4 respectively. No relay, or field coil signal required.

10 minutes ago, ColinJB said:

Originally a load of stuff connected to POS #2 on switch with piggy back terminals!

This is not unusual.

10 minutes ago, ColinJB said:

Very close to rip it up and start again ;-(

Sometimes you just have to take off and nuke it from orbit. It's the only way to be sure. However, you need to understand what you are going to replace it with.

[Tony Brooks]

14 minutes ago, Jen-in-Wellies said:

GN connects ignition switched 12V to the bulb to the W connection of the alternator. When the engine is stopped, or the alternator is not working, then there is current flowing through the bulb to the alternator and the bulb lights. When the alternator starts charging, the W connector rises to 12V and no current flows through the bulb and the bulb goes out.

 

Sorry Jen, I am sure this is a simple slip. W  on the alternator is the phase top/ Rev counter terminal. I am sure that you meant D+ warning lamp terminal.

[Jen-in-Wellies]

1 minute ago, Tony Brooks said:

 

Sorry Jen, I am sure this is a simple slip. W  on the alternator is the phase top/ Rev counter terminal. I am sure that you meant D+ warning lamp terminal.

Yes, my mishtake. Should be D+.

[Tony Brooks]

The need to understand what the OP is dealing with is why I posted my diagram. In fact, I think that before he starts any work he would be well advised to read the relevant parts of my website - in the electrical notes.  tb-training.co.uk

[Onewheeler]

4 hours ago, ColinJB said:

Control panel wiring best described as "rats-nest". 

In case it's any comfort, when I bought my boat 30 years ago I spent a while looking at the wiring behind the panel. I then spent an hour with wire cutters and filled a carrier bag with wire. Everything still worked and I understood most of what went where.

[ColinJB]

Thank you all.  I've now got some good hints on what to try next.  I think an extension cable to the ground lead on my multi-meter would help.  Otherwise grow longer arms 🙂

I will have a look at Tony's website.

A diagram, even a confusing one, is better than enduring a 20min YouTube video that "might" contain 5sec of useful information?

Perhaps I'm showing my age?