No Ignition light

[swordfishdani1960]

Have had the car for years ,never have i had working
ignition light,have check the light its good ,battery is charging
all cables are connected to alternator 3 off, Brown yellow return to ignition connected , all other lights are on the dash oil, hand brake seat belt warning light on before you crank engine
any body any ideas

[FI Spyder]

With ignition in on position (engine off) you should have 12V at the brown/yellow wire that goes into the alternator. It gets the 12V from the light. I thought the light was in series, no light no 12V. How did you check the light bulb? Visual or by ohm meter. I never trust visual for either lights or fuses, always use ohm meter.

[swordfishdani1960]

Bulb is good, no 12 volts to alternator, check cable from light to alternator all good with a meter

[swordfishdani1960]

Have checked behind ignition light
bulb, there is 12 volts when ignition is turned on
but there is no voltage on the Brown yellow at alternator .
Brown /yellow cable has been metered out its ok

[FI Spyder]

If there is 12 volts at the entry point to the bulb holder and none at alt but wire measured continuous and the bulb measured good by giving a few ohms then that leaves only one thing, a bad bulb holder. Don't measure voltage at one point and assume it's present over there, ie. is there 12V on the printed circuit where the bulb holder contacts it or is it broken somewhere before.

[Tamas Petrunin]

With ignition in on position (engine off) you should have 12V at the brown/yellow wire that goes into the alternator. It gets the 12V from the light. I thought the light was in series, no light no 12V. How did you check the light bulb? Visual or by ohm meter. I never trust visual for either lights or fuses, always use ohm meter.

Err that's not quite correct, if the brown/yellow wire is disconnected from the alternator then you should see 12v on it, however if it is connected to the alternator and the alternator is okay then you should see 0v on it when the ignition is ON and the engine is NOT RUNNING, when the engine isn't running that wire to the alternator effectively provides a ground connection for the ignition warning bulb.

The bulbs for Ignition, Oil, Brake, Choke, Low Fuel all share the same ignition switched 12v supply and they all light up when they are given an ground on their other connection.

The Ignition warning light is slightly different in that when the engine is running the alternator supplies 12v to the one side of the bulb and the ignition switch suppplies 12v to the other side of the bulb so there is no voltage difference across the bulb so it goes out, with the ignition ON and the engine NOT RUNNING the alternator provides a ground for the bulb and so it lights up.

I hope that makes sense.

[FI Spyder]

That makes sense. When I measured mine I had the yellow/brown wire off alternator where I got 12\v at the wire. With the wire connected to the alternator I didn't have the ignition light come on, not because I didn't have 12V or that the bulb was burnt out or that the wire was bad but because the alternator was knackered hence no ground. New 1996 Saturn Alternator, all is well.

[swordfishdani1960]

The only cable that has voltage is the heavest which is the middle connection on the alternator 12 volts the other 2 i.e. brown yellow 0 volts brown wire 0 volts when ignition is turned on ,but not running , this check is done when cables are disconnected from alternator
this beats me ,

[FI Spyder]

Somewhere between where you get the 12V and end on yellow/brown alt end where you don't there is a break. It can be where there is a connection or it could be a break in the wire. When doing an ohm check between two points be aware that if there is a break in the wire (in the insulation or at connector crimp) it may make in one position (when measuring) and not in another position (at rest).

[Tamas Petrunin]

Have checked behind ignition light
bulb, there is 12 volts when ignition is turned on
but there is no voltage on the Brown yellow at alternator .
Brown /yellow cable has been metered out its ok

When you checked behind the ignition light did you check the bulb hadn't blown ? If the brown/yellow wire to the alternator isn't providing an earth as it should (ignition ON & engine NOT RUNNING) then there should be 12v on both sides of the bulb ?

The only cable that has voltage is the heavest which is the middle connection on the alternator 12 volts the other 2 i.e. brown yellow 0 volts brown wire 0 volts when ignition is turned on ,but not running , this check is done when cables are disconnected from alternator
this beats me ,

Going off the diagram in front of me, both the brown wires should have 12v on them all the time, both of them get 12v from the battery.

Personally I'd test that the ignition bulb lights up when given an earth, if you look at the following picture...


with the ignition ON the bit I've coloured red should be 12v and the bit coloured green should be 0v, if you have 12v both sides of the bulb then temporarly run a wire from the bit I've coloured green to a earth and see if the bulb now lights up.

Ok now we've proved the ignition bulb works I'd now remove the brown/yellow wire from the alternator and earth it, if the bulb now doesn't light up then you have a break in that wire and will need to follow it along the loom to find and repair the damage.

Once the ignition bulb lights up when the brown/yellow wire is earthed we can put it back on the alternator and test some more.

That's enough to be going on with....

[swordfishdani1960]

Last diagram was help full .I passed 12 volts thru B/Y cable at alternator end
removed 8 pin plug going into printed circuit board, got 12 volts at cable .
Plugged back int circuit board ,removed light ,no 12 volts at NEGATIVE,side of light
remove fascia board ,discovered braKe in the blue plastic board ,RE SOLDERED
printed circuit board, now have ignition light working ,which i never have had
thanks all you nice people that made this possible
This fault possibly left the BL FACTORY WHEN NEW
cheers

[Tamas Petrunin]

Glad you got there in the end