Mini voltage gauge. Drill a small hole in dash, wire to any handy 12V source, and I guarantee that someday it will save you from a dead battery. Sorry for the photo, Iphone doesn't resolve the red numerals too well. These are all over e-bay for about $5, including postage from China.

Attached Thumbnails

 

Seriously?A true MB fan dont drill holes in the original panels for a china meter...

A true driver doesn't drive old cars without voltmeters.

If you don't like this one, you can get a VDO for $45, or an original voltmeter from a 16v Cossie for $150. Think about it while you're waiting for the tow truck.

Thank you MX i am looking right now for one ..

I bought a round black voltmeter with an ivory colored needle and numbers. Matches the other instruments in the car. I placed that where the antenna up/down switch was.

And due to the notorious electrical problems with these cars, I depend on that voltmeter for information. Just had a belt squealing/slipping problem. I saw that the voltage was 12 volts when squealing, then 13/14 volts when it stopped squealing! So I knew the culprit was the alternator belt.

You can also get voltmeters which plug into a cigarette lighter (on Mercedes they are called "cigar" lighters!)

I just use my dash...when all the lights come on, the alternator/regulator is no longer charging.

I also carry a portable 12V battery/jump charger and a dead battery is a non-issue. I'd rather spend $60 on the battery than drilling holes...

__________________
2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

This^

The reader will tell you when you're battery is dead, but that does nothing other than state the obvious. Keeping the portable charger on hand is what matters. Also keeping a voltimeter on hand will also help in diagnosing a loose belt, faulty regulator, or a disconnected cable.

__________________

1990 190E 3.0L

A portable jump charger won't help with a bad alternator. And there are failure modes that won't cause the dash to light. But you can admire your pretty dashboard while you wait for the truck.

It won't, but neither will the 12v gauge. I carry a survival kit in the car, as I'm sure most do, which includes spare fuses, bulbs, hoses, a belt, and an extra voltage regulator, etc. These are just a few basic things that can help if you run into problems while on the road. Of course, none of these items would do you any good when faced with catastrophic failure of a fan bearing bracket, a severed ball joint, or a disintegrated flex disk. Either way, the only real assurance is the roadside assistance.

__________________

1990 190E 3.0L

Not a word about preventative maintenance? Do you just wait until something breaks? How about KNOWING the installation date on your battery and plan on replacing it 5 years later? How about replacing the regulator on the alternator every 70K? How about new belts, coolant and idling pulley every 100K? And for the 8 and 12 cylinder guys, how about the "tee" fitting and hoses every 100K. And don't forget about that nest of vacuum hoses on top of the 119 engines. I just replaced 12 coils and 12 plugs because they were 18 years old. And to be doubly sure, how about the 200 mile towing package on your AAA card?
Sorry I'd rather carry a bottle of wine, a corkscrew and some glasses than half of my garage tools the next time I planned a 1000 mile trip into Utah.
Anziani
'97 CL600
56K

I did this and instead of drilling holes I rigged it with velcro - my display was red, while being stopped by the cops after sunset for some odd issue like a 2 mph speeding warning - the cop lost his marbles and called backup assuming it was some sort of weird timer.

Use it with a switch or something..

__________________
2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

I agree with the concept of monitoring as many parameters as possible. In addition to voltage, I also monitor EGT, fuel pressure, engine bay temperature, vacuum, intake temp, boost, oil temperature, transmission temperature and engine elapsed time.

Rather than use individual gauges, I collect the data using sensors and an Arduino which then sends the data to an Android tablet over Bluetooth. I have a library of screen presentations with analog gauges, ribbon gauges, digital gauges...and even a simulated Nixie Tube set. The tablet is mounted in the horn pad, so it's also available for navigation and a HUD showing speed, direction, altitude, elapsed time, average speed, etc.

Here's one screen.

__________________
Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

I won't be drilling any holes in my car. If I need a volt meter that badly, they make some that plug into the cigarette lighter port. Unless you are taking the reading directly from the battery terminals, it won't be accurate since other accessories share the circuits the gauge is tapped into.

__________________
1991 F250 super-cab 7.3 IDI. (rebuilt by me) Banks Sidewinder turbo, hydroboost brakes, new IP and injectors.
2003 S430 - 107K
1983 300SD - Tanoshii - mostly restored ~400K+.
1983 300SD - Good interior. Engine finally tamed ~250K.
Monark Nozzle Install Video - http://tinyurl.com/ptd2tge

Nonsense. The variance from battery voltage is insignificant. What's more important is that there's a 1.5-2V spread between observed battery voltage vs alternator voltage. That really helps give early warning of problems. For example, it prevented me from driving off with an open field winding, a fault which can't be detected by the idiot light circuit.

Do you really think this is uglier than a gadget sticking out of the lighter socket? To each his own.

Mach 4, That is absolutely brilliant. I wouldn't want to permanently mount it on the steering wheel but what a great idea. How, where did you find the sensors for the interface? Of course I have a 120 that gives "0" room in the engine bay for anything else. If you are ever in the Palm Springs area, let me know. I'd love to see your set up.
Anziani
'97 CL600