My Voltmeter Install - 328

Well, Greg328 got me motivated to get my voltmeter installed correctly in the 328. Previously, it had been in a bracket underneath the AC (actually, where my Equalizer is right now). A neater installation would be in the left-hand coin pocket, where gauges were originally mounted in the carb 308s.

Some folks are fine without a voltmeter, I personally think it's a very good gauge which speaks volumes as to how the electrical system in the car is operating. That said, its operation is a bit redundant next to the "G" Generator (alternator) light in the car. I prefer having the gauge though, to see the numbers, to confirm the alternator is charging, and to know if (when I'm working on the car, say) running the radio is risking weakening the battery (below 11.5V, say).

The voltmeter of choice is the VDO "Vision" series lighted gauge. I've found the gauge to be of very high quality. I purchased it from egauges.com (no affiliation), for $26.44; here is the direct link to the product: http://www.egauges.com/vdo_mult.asp?Type=Voltmeter-12&Series=Vision&Cart=. (For reference, the installation manual can be found here: http://www.egauges.com/pdf/vdo/0-515-012-068.pdf).

The tricky thing is the mounting bracket. I basically custom fabricated my own bracket to fit in the left hand coin pocket (see pics). I started with a double-gauge, black metal bracket with two round holes machined out. (I don't know where to find these now; this was on my previous 308 from the previous owner.)

Very important to use a lighted gauge, or else you won't be able to read it at night! Of course, you'll need to wire the lighting circuit separately.

The easy approach to the wiring is to splice into a switched voltage +12 ignition wire (easy to find if you have the wiring diagrams!), fuse this, and then run it to the voltmeter. I personally chose to use a relay, because I wanted to measure current most representative of the battery, not an ignition wire after the ignition (ignition wire is usually used to activate relays in the fusebox, anyway--it won't necessarily carry a voltage equal to that of the battery).

On a side note, for the lighting circuit, you'll want to tap into the hot leads AFTER the dimmer switch, say, the same ones the instrument lights use, so that (if you use the dimmer switch) the voltmeter will be similarly dimmed. You also need to do this of course so that the voltmeter lights up only when the parking lights or headlights are on.

My wiring was as follows. First, I bypassed the dimmer switch (not needed, and I wanted brighter lights; there is a voltage drop in the dimmer switch rheostat / variable resistor, check out thread http://www.ferrarichat.com/forum/showthread.php?t=63787). I rerouted the (now unused) ground originally going to the dimmer switch (a strong, factory chassis ground) and that became the Relay ground and gauge lighting ground. (Note: according to installation instructions, gauge lighting ground needs to be a different ground than that used for the actual voltmeter gauge itself.) I decided that instead of running a dedicated lead from the battery, the current I would measure with the voltmeter would be that of the trouble socket (convenient to get to), which is of course fused. I split this, and the new lead became the +12V into the relay. I found a switched voltage ignition wire, split it (by the way, I didn't use wire taps - and nor should you), and this became the "activation signal" or "turn on" lead into the relay. Thus, the voltmeter only operates when the ignition is in the "Run" position. The output or "turned on" voltage from the relay then goes into the voltmeter "+" terminal. The fifth terminal on the relay, in accordance with a "turn on" relay, is not used.

I worked very cautiously from the experience with all the electrical work I did in the 308, as well as installing remote entry just recently the 328. Good strong insulated crimped connections, judicious use of electrical tape, not using wire taps, etc. All wires were tucked up and wire tied wire the factory wires, looks factory.

I drilled a small (3/8" or so) hole in the back of the 328's coin pocket, behind the felt so it can hidden and restored to stock if the voltmeter is ever removed. The four wires that connect to the voltmeter were routed out of here, right in the vicinity of the trouble light socket, my relay, and the dimmer switch wiring.

That's about it... Net result is a very nice working voltmeter. The VDO voltmeter itself reads about 0.2V low according to my radioshack voltmeter; this could just be a calibration thing. In testing, it reads about 12V before I start the car, then about 13.5 when the alternator first starts charging the battery. I haven't checked out steady-running, battery-already-charged voltage but I expect that to be 12.5, 13.0V.

Edit: This thread may also be of use:
308 voltmeter? Anybody ever installed one?
http://www.ferrarichat.com/forum/showthread.php?t=63607

P.S. This is just my way of doing it. Verell had a great idea to use a rotary switch to select the voltage source being measured (Off, Ignition, Battery, after the fusebox, etc.). I personally just decided to go with measuring the trouble light socket voltage as a useful approximation of system voltage.

Hope this helps!

--Mike
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Martin,

That's a great suggestion! I've been toying with that. The thing is, I tried the red cap before--it came out a shade lighter than the other gauges.

I was thinking of actually "double bagging" it and putting on TWO red caps over the bulb--this might bring the red tones of the VDO gauge in line with the other stock gauges... Will try this soon.

Underscoring your point above, I'm a big fan of the voltmeter... One thing it shows that the Generator dummy light does not is OVERCHARGING. In my 308, the voltage regulator failed in the alternator, and the battery was being cooked at 16V, 17V. So was everything else (not good). We eventually think this was related to ignition coil damage on one bank, almost causing a fire (I did melt a cat that day--November 2002 back in the old 308 [now sold]). The battery also exploded and was rendered useless as a result (typical from being overcharged).

 

Update:

Per Martin's suggestion above, I have used the red cover on the bulb to get a more stock light color in the voltmeter. I actually used two red covers (had one from my VDO ammeter, not currently in use).

The result is basically the identical color to stock. It's a bit lighter in the pictures, but in practice inside the cabin the difference is not noticeable.

After a week or so with the voltmeter, I'm definitely a big fan!
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