8 replies to this topic

[jasonmallett]

Having a full rebuild of the mini and all new wiring. Been looking at wiring diagrams so get a plan of what to do but single indicator bulb is confusing me as it has to wiring like the rest but one from left and one from right but no ground. 27. Also the ignition light. Number 44 is the same just asking how this works. As being an electrician all of our lights need a neutral and live to work. Page 12A-21 Haynes 0646

Cheers Jason

[gazza82]

Might be earthed through hokder and speedo unit. Some older cars had earth cable on instument brackets.

[jasonmallett]

That's what I thought but all bulb holders have 2 cables so not 100% sure

[Dan]

The ones that earth through the instrument case are the easy ones to understand. The repeater lamp grounds through all the lamps on the unused side of the indicators. The volt drop through the repeater lamp results in there being too little current present when shared through all the lamps in the rest of the circuit for any of them to actually glow, but they do conduct to earth. It's more or less same for the ignition lamp. When the alternator is not generating current the warning lamp cable carries current away from the lamp and grounds it through the alternator circuitry, so the lamp lights. As soon as it starts generating the lamp sees bus voltage at both terminals and there is no current so no glow. The cable runs to a separate output terminal in the alternator which is not common to the rest of the output so the lamp can discriminate between the alternator generating and simply being hooked to a battery. This terminal also provides the startup current, through the warning bulb, for the alternator circuitry so if the bulb is blown or missing the alternator won't charge. These two lamps, along with the oil pressure warning where fitted, must absolutely not use grounded single terminal bulb holders. They must be fitted into two terminal insulated holders.

[jasonmallett]

Ok understand that. Mine uses doesn't have an oil presume light it has a gauge I think. It's a 72. Ok understand that but if you can only buy one sort of bulb holder. With a red and black cables I take it they all work the same just wired differently as in no - supply as you said above?

[dklawson]

See if the following accurately paraphrases your question....

"I can only buy one type of bulb holder and it has two wires, red and black.  Can I use it in place of all these different bulb holders on a center speedometer?"

Is that what you are asking?

 

If that is your question, yes, you can use the two-wire bulb holders in place of a one wire bulb holder.  For any single wire lamp (gauge illumination, high beam, etc) you can earth the black wire to the speedometer case and use the red wire for the "hot" wire to light the gauge.  On the two wire lamp circuits such as the charge warning light and the oil pressure light, run the red wires back to the switched (white wire) leaving the ignition switch.  The black wires from these bulbs get spliced to the wires going to the alternator (small brown/yellow) and the oil pressure switch (white/brown).  I forget what is required on a turn signal circuit but I believe Dan has provided that above.

[jasonmallett]

Ok that basically sums all my questions up. Thanks dan and dklawson but you too keep mentioning oil pressure switch. I don't think I have one as it a mechanical gauge?

[dklawson]

Some cars have oil pressure warning lights, some don't.  If you car has an OP switch, that warning lamp uses a two-wire socket.  Current flows from the white wire on the ignition switch, through the lamp and off to the engine mounted switch via a white/brown wire (2 wires).  Again, some cars have that light and switch, some don't. 

[jasonmallett]

Ok that make sence so I don't think I have one. Cheers for the help