I thought this would be an easy add-on, but maybe not. Does anyone have any info on adding a digital voltmeter? I'm keeping all of the original instruments as-is—including the ammeter, however I thought it would be a good idea to add a voltmeter. The voltmeter itself is simple; I'm just trying to figure out where it gets wired to (without changing any of the original wiring). Can the pos go the fuse box with the neg to ground? (yes, mine is the later neg-earth system) Or does it need to go to the alternator or some place ahead of the fuse box?

Whenever I work with electricity, I realize how little I understand it.

 

I am absolutely not a car electrician but that is meant to go in place of the cigarette lighter. I installed one recently in my 2012 MBZ S550. The hard part was YouTubing how to remove the center console. I found a great video and it took all of about 20 minutes. The car was relatively new with only 30,000 miles (but 8 years old and the battery was failing. The two plugs take the exact 2 plugs of the cigarette lighter which is simply a live wire and a ground. If you want to keep a cigarette lighter then you can simply take a jumper wire from any positive lead and connect the negative wire to the chassis or to the bundled grounds found anywhere. Like being able to charge my iPhone and know my alternator output is correct. I don’t smoke so the cigarette lighter is only used to charge the phone anyway, but with this device you can do both. Good luck.

 

I would connect to a fuse that is powered on/off by the ignition switch. That way the voltmeter will not draw current when the engine is off. If your wiring is like mine, fuses 6 and 7 are the ones. Use a spare lug, preferably on the hot side of either fuse. On my car that wiring is white. There is some voltage drop through the fuse and its connections so connecting to the hot side is more accurate. You can connect to the lighter if that is more convenient as long as the lighter does not work with the ignition off.

 

Thanks for the input. I went ahead and invested in a basic multi-meter (my knowledge of which is extremely limited). Anyway. it appears that the on/off switch on the face of the device controls both the voltmeter and the USB circuit. I'm thinking that since I can switch off the gauge manually, to wire it outside of the ignition switch circuitry. I guess anywhere on the hot side of the fuse box would be OK, fuse #3, or maybe tap off the cigar lighter? But yes, if it does make more sense to run it through the ignition switch, I see that fuses #6 and #7 are the ones to go to.

A related question would be which fuse to wire the stereo to? I thought fuse #4 was a spare, but I'm not so sure now. The schematic has #4 going to the fuel pump. My car is a 4.2 S1 made in early 1966 (#1E-21198).

 

Good that you are getting a meter. I checked my car's schematic and the standard attachment is to the input to the voltage stabilizer mounted to the back of the instrument panel, This is wired to the load side of F7. You can do that also, I see the on/off switch in your photo but do you want to bother with that? Incidentally, my car is a 68 but I think the wiring of interest is the same,

Connect the stereo to the lighter but check that the lighter works only when the ignition is in the on or aux positions. Then you can listen when parked. This should be F4 and should not power the fuel pump. Turn the key to aux while listening for the pump to operate. If it does, I think some rewiring has been done. It should go to F6. Good luck.

 

I'll have to trace down some of the fuse circuitry—there seem to be minor changes during the 4.2 run. My ignition switch does not have an AUX position (which is why I may want the stereo out of the ignition 'on' circuits. I just need to make sure it's not drawing power when off. The car is in the shop so all of this is now on my to-do list.