Alternator Light Bulb Change

[Funracer]

Neither my alternator nor my OXS bulb come on with the key turned to ignition position. Pulled the druck oil guage. There are a couple of white back light bulbs there but the alternator light bulb looks to be in a different type holder.
Found the Bentley wiring diagram looks like the Alt light powers the OXS bulb? Checked fuses all look good.

Anyway tomorrow I will check the Alt bulb. Anything tricky about getting to it?

Thanks

[7783911]

make sure its the correct bulb as on g models it acts as the circuit to trigger the alternator (exciter)..wrong bulb and no charging..ask me how i know :-)

[Funracer]

Pulled the ALT bulb it has continuity and does not look burned. Probably OK

Dome light works so that fuse is good.

Saw the dark diode removed it and plugged wires together. Still no ALT or OXS
light and battery still not being charged.

Next I will check OXS bulb but I doubt that is the issue.

What can I check next? Is there another inline fuse somewhere for the alternator?

Thanks

[7783911]

the bulb has to be a specific wattage for exciter circuit to work, I bet Timmy would know

[Funracer]

It’s the same bulb that was working before. I have not changed the bulb

[DNickel]

This has me worried a bit. I have an '88 and changed all the dash bulbs to LED last year. Haven't had any charging issues that I have noticed. The Alt bulb comes on as usual until I rev a bit and then goes out as normal.
Should I be concerned about putting the incandescent lamp back in?

[timmy2]

Originally Posted by 7783911

the bulb has to be a specific wattage for exciter circuit to work, I bet Timmy would know

BA7 bulb, IIRC it needs a 4 watt for that year.

[timmy2]

Originally Posted by DNickel

This has me worried a bit. I have an '88 and changed all the dash bulbs to LED last year. Haven't had any charging issues that I have noticed. The Alt bulb comes on as usual until I rev a bit and then goes out as normal.
Should I be concerned about putting the incandescent lamp back in?

If it is working, don’t worry about it.
Sounds like it is working correctly.

[Arne2]

I had a regulator fail on my '84, when it failed the alt light did not come on with the key, and it did not charge at all. The car was new to me at the time, and I didn't notice the light wasn't working, and the battery died while I was driving it. You may have a similar problem.

[Funracer]

Just to fill in the details I had the alternator rebuilt last week and put it in yesterday. Went by the alternator shop today and guys says the alternator tested perfectly. It been in business 40 years and all they do is alternators and starters. He seems to think there is no power to the light through the ignition switch. How can I verify that. I stink at electrical stuff so keep it simple or point me somewhere that has a grade school level test.

[Funracer]

Tested bulb checks good

OXS socket getting 12 volts.

ALT socket getting no voltage

[Funracer]

Strangely there was no bulb in the OXS socket. Which is strange because I have seen it on before.
In any case I will replace the bulb and go from there.

Anyone know the bulb specs?

[Funracer]

Got it! Pulled the alternator out to return it to the rebuilder and noticed the loose wire.
Cleaned the spade post and reattached and did a quick key check to ignition and both OXS and ALT lights came on as they should. Can’t finish the install til tomorrow but all should be well.

Thanks

[gptom]

After a year, I just had to take out LED bulb and return to incandescent bulb. rest of dial lights still LED

[DNickel]

Thanks for the reply guys. When I break out the car this spring I will monitor the charge rate from the Alt. If my battery seems to be not floating properly I will put the 4W bulb back.
Don't really want to be stuck somewhere with a dead battery because of my stubborn nerdiness.

[spoke]

Originally Posted by DNickel

This has me worried a bit. I have an '88 and changed all the dash bulbs to LED last year. Haven't had any charging issues that I have noticed. The Alt bulb comes on as usual until I rev a bit and then goes out as normal.
Should I be concerned about putting the incandescent lamp back in?

It's never a good idea to replace the GEN/ALT lamp with an LED. This light should always be an incandescent light of the proper wattage.

The GEN light serves 2 purposes:
1) Provides initial current for the armature to bootstrap the alternator into its operational state.
2) Should the diodes in the alternator which charge the battery fail, the battery voltage will now be less than the voltage regulator voltage and current will flow in the opposite direction and light the lamp gently depending on the difference in voltage. An LED will only light in one direction and won't alert you that there is an issue.

When you say the ALT bulb is on "until I rev a bit" is a sign that the LED isn't working correctly. Normally as soon as you start the car and the engine runs at high idle the alternator should bootstrap itself and work normally with the light out.

[r lane]

This may have been stated, but the alt light has voltage to one side when the ignition switch is on. the other side is a blue wire that is grounded at the alternator, and the light should be on. When the alternator starts spinning, the ground signal begins to change to voltage. When that signal (blue wire)gets to within 1 1/2 volts of the other side, the light goes out. So see if with the KOEO, you have 12 V to one side and ground to the other. I suspect no ground and you will have to trace it back to the alternator. Bob