1983 300D - Electrical (or what I did to my W123 today)
 

So, I played with my '83 300D. I am going to post in the follow-up post what all I did, in case you guys are curious; here are my two outstanding issues that I have not figured out yet

- the brake light remains lit, very faintly; it is an LED, so, maybe its just the LED is more sensitive than a regular light bulb will be?

- after I start the motor, the voltage at battery measures 12.7 V *until* i rev the engine up a bit. Then the voltage jumps to 13.8 - 14.0 V. Is that normal, and if not, what's broken? The alternator tested OK (I took it out and took it to Oreilly and they tested on their machine)

Check the tail light ground. W123 cars normally do not like LED bulbs. Try the original bulb. Charging voltage could be a little higher about 14.7 volts. Check for slipping belt, corroded battery cables, corroded engine ground strap.

Not knowing your specific car, I'd say the bulb out monitor is applying power to the bulb looking for continuity. If not this, perhaps the cruise control bleeding back or a trailer light adapter bleeding ( that converts a Euro 3 filament to US 2 filament )

Does this only occur when the parking lights are on? If so, you have a poor ground for the rear lights.

As for the alternator waking up, this occurs on some cars in general when the idle speed to too low, alternator warning light can't pass enough current / is missing.

Detailed list of what I did
 

And now, the more interesting (well, I think it is) part of the post.
Its a long story and there is suspense about 2/3rds down

A few small odds and ends were bothering me about my W123 and so I decided to address them. Specifically

- the clock wasn't working
- the radio wasn't working right -- would not stay on freq. and was weird
- wanted LEDs as instrument cluster backlight
- Speedo needle was binding (magnetically) to the stop post

To address these things, I did the following:

- clock: replaced the 100 uF capacitors. success, clock works.
- radio: replaced with a Kenwood HD-262U (I like the digital HD radio because its a neat tech so I always look for it in aftermarket radios)
- speedo: stripped black insulation from a wire and used that instead of the thin clear plastic OEM insulators; have not tested yet b/c see below
- LEDs: replaced backlight, turn signals and everything else with LEDs. Went back to regular bulb for battery warning because some of those LEDs are polarity sensitive

While I was doing all this, I unintentionally broke the following:

- the door strikers; I guess it was time and I know that plastic gets brittle, so, four new strikers are on order now

- while figuring out the radio memory retention and cycling the ignition on/off/on/off... the glow plug light stopped lighting up... following dieselgiant's troubleshooting directions, identified failed glow plug in #1. Replaced; all good now.

- pass. side window switch; just stopped working; I've cleaned it before; I think this time I am going to just replace it. I tried the front window with the other side's switch and it worked. The rear pass. side window I think has more problems but right now I don't care...

- Oh yeah, while figuring out the door striker, I put a screw down there to see if I could shut the door... It did and then I spent two hours trying to open it.

- Measured only 12.5 V at the alternator. Took it out, took it to OReilly, it tested ok, re-installed it. I got my uninstall/install time down to like 10 minutes, good practice, right???

This is all in a span of about 6 hours, including the trip to OReilly. If I think about any other juicy details I'll post them.

Both brake lights work and I don't think my car has a 'bulb out' monitor. its a 82 300D, pretty plain.

Cruise control is not working anyway, I'll try disconnecting its wiring and see what happens.

Parking lights on/off, doesn't matter. I am planning to replace the brake warning light with a regular light bulb and see if it stops glowing.

In all I had a great Thanksgiving and then while the rest of my family (all women except my 5 mo. old grandson) visited and talked and stuff I had a great day with my W123 :)))))))

Assuming its drive belts are properly installed and tensioned, you didn't make any specific mention but; the voltage regulator installed in the alternator should be checked and verified that its brushes are still serviceable. That's what effects the greatest control over the output voltage.

Would a faulty voltage regulator prevent the parts store machine from diagnosing it "PASSED" ?

Good one, will check. That one is often overlooked...

Starting to see that now... original bulb for the brakes is destroyed, will get a new one tomorrow.

I will check for the ground strap.... I am not even sure I've ever seen one on my engine, so, will have to look for it...

Thanks!!!

Sorry, I don't have any idea how they test nor what parameters constitute "passed". Your description is clear that insufficient voltage is being generated at idle and low RPM, that can only mean a couple things, loose belts not turning the alternator fast enough or some malfunction with the voltage regulation system. You've R&R'd the alternator so I'm assuming you tensioned the drive belts correctly when you reinstalled it, you made no mention of checking it so that leaves the voltage regulator as the next logical step.

It's held in by a couple screws to the rear side of the alternator, with a stubby screwdriver it can usually be pulled and checked fairly easily and quickly.

Engine ground is on the Driver's side, a bare woven copper braid between the bell housing and the chassis.

I can pull the regulator, no problem... at this point I can either use the stubby screwdriver or just pull the alternator, I've got the removal procedure down pat at this point...

Just finished cleaning all the window switches... soaked contacts in carb cleaner, shined and reassembled... all the front windows work, rear windows don't... sure does sound like ground issues, doesn't it... :D

Just keep the stock light bulbs ,I tried a fancy route in my license plate bulbs ,they melted the housing and burned out quicker.

No rear windows from the console switches nor the door switches? The "child lockout" switch is verified as functional and not set to disable rear switch control?

You can test what's getting to the switch in the door by just pulling it out to get to the wiring connector, but if you're not certain your probably going to need to verify the window lift itself operates, so you'll be taking the door card off to get to that.

I don't consider those voltage numbers problematic. It's not discharging at idle and comes up to an adequate voltage after idle. I wouldn't do anything or worry about it.

Is the alternator regulator the proper Bosch or an aftermarket?
Is the proper charge indicator bulb installed?

On my Volvo 245 from that same era with the Bosch alternator/replaceable voltage regulator the sign of a bad VR was intermittently/randomly dimming and flaring of everything on the electrical circuit. Most noticeable on the headlights and dash lights when it was dark. You shouldn't have to pull the alternator to change it, at least I didn't on the 245.