Electrical confusion (1 Viewer)

[bx75]

Hi all,

I’ve got a 1975 non-US FJ40 and am getting rather confused by a PO’s wiring!

ln the dash cluster the ammeter gauge has been removed and replaced with a bulb that has been soldered into the circuit. The alternator isn’t standard and appears to be for a Mitsubishi- could this be why the gauge has been removed and can I just add one back in?

Also odd is that the coil resister is only wired in one end? Is this normal?

Thanks in advance!

 

[South Texas 97]

Go to @Coolerman site and pick up a circuit diagram for your year/model of FJ40. This will help you figure out what goes where.

If only one end of your coil resistor is connected, then it is not doing anything.
The electrical diagram will tell you where it should be connected.

On the lamp on the instrument cluster - it looks like the PO tried to made an idiot light. but not sure how this would work.
Greater minds than mine will weigh in, I am sure.

 

[trainbufftony]

The coil may be disconnected due to a points delete type kit, a pertronix, Mallory optical, or similar...
As for the ammeter, I'd start by replacing it, see what happens.

 

[Vandal FJ]

Be sure and check the year... mine is a January 1972... which means I need schematics from a 1971! The 1972 covers September on.

 

[Living in the Past]

The resistor is there to reduce the spark after starting. It's bypassed during starting for a hotter spark. If both wires are landed on the same terminal possible the resistor is bad and this was the fix. It will run just with the hotter than designed spark.

 

[charliemeyer007]

I suspect the idiot light works with the current alternator, which might not support a meter. Look for changes in the wiring.
Does the system charge and indicate correctly now? If so you should figure it out before you change stuff and go to a non working system.

 

[pb4ugo]

You need to determine if the replacement alt has a internal voltage regulator or not. The removal of the ammeter and the added idiot light means the PO did make some changes to the charging system.

 

[bx75]

Thanks for all the replies. Please excuse my ignorance, but what’s an idiot light?

I suspect the alternator is internally regulated as there’s no external regulator I can find- would that stop the ammeter from working and be the reason it was removed?

 

[charliemeyer007]

Idiot light tells you the system isn't charging at the minimum setpoint. It doesn't tell you about excessive charging or how much more than the minimum its charging.

 

[pb4ugo]

If the alt quits working the light turns on. An alt can be wired with the ammeter or without. I think, Coolerman sells a mini wiring harness to make the ammeter work with an internally regulated alt. The use of ammeters is old antiquated and most auto makers don't wire their cars that way anymore. Madelectrics website has good tutorials on alt wiring, along with info on a charging system with an ammeter.

 

[bx75]

Thanks, will give it a look!

 

[45Dougal]

Id also guess that is an idiot light. The idiot light normally goes between the 12v feed from the ignition switch and the field wire on the alternator. Disconnect it and you'll stop charging.
Test the light by reducing your idle - it will come on when the engine gets too slow or stops.
There are two ammeters depending on year. Your cluster looks like the new type which uses an external shunt.
An alternate guess is that the light replaces the shunted gauge - it will only then come on when the battery is charging or discharging heavily.

Buy a meter.
Print out the correct wiring diagram for your year and start scribbling corrections on it as you go.
Good luck

 

[Engineer8000]

Looks like the Mitsubishi alternator supports a charge light, this is the wiring for a lancer.