Changing an Amp gauge for a Volt gauge

[grannyknot]

I have heard and read in the archives that there is a few years where the 260z and or the 280z had a

Volt/Fuel gauge that can replace the early Amp/Fuel gauge. None of the threads I found listed which years the Volt/Fuel gauge came in or really described the change over. I know I have to connect and isolate the charge wires going to the Amp meter but wondering if anyone has done this change over and could add some detail?

Thanks,

Chris

[SteveJ]

I haven't done it, but it's not that difficult.

Following the FSM wiring diagram, you can see the wires that go to the ammeter. As you said, those wires must be joined together. Insulate your connection well, since you definitely don't want a dead short there.

You will need a voltmeter/fuel gauge. From CarPartsManual.com, it looks like it will come from a 77 or 78. You may have to modify your dash harness and/or meter to get the same plugs on both sides.

Run the negative side of the meter to ground.

Run the positive side to a constant 12VDC or switched VDC, depending upon whether or not you want the gauge to be functioning when the power is on. A voltmeter has very high resistance, so the power draw is negligible.

[grannyknot]

Sounds easy enough, and then I guess I would connect up the L terminal or #1 to the charge light in the voltmeter, right?

[HusseinHolland]

Going to piggy-back off this old thread rather than make a new one - the goal for me is to add a Voltmeter, (three gauge pod, replacing radio - I need to add a WBO2 in prep for the V6 conversion) not replace the stock ammeter though.

Trying to figure out which wire in the dash harness would make sense to tap into, to get an accurate charging voltage value. Something from the Voltage regulator would seem to make sense, however I have a hard time cross-referencing these old line diagrams against the schematics. 

Any pointers?

I'm assuming the C-x connectors are the ones at the fuse/relay panel

 

 

Edited September 30, 2023 by HusseinHolland
add pic

[SteveJ]

Instead of cutting into an existing wire...

Use what's already in the dash. On the clock, there is constant power at the LW (blue/white) wire.

There is switched power at the L (blue) wire on the water temp/oil pressure gauge.

You would need to get two male shells (https://www.hi-1000ec.com/product/1133) and two female shells (https://www.hi-1000ec.com/product/1135) along with male pins (https://www.hi-1000ec.com/product/1662) and female pins (https://www.hi-1000ec.com/product/1663) to go in those shells. If the meter doesn't require constant 12VDC, you only need one male shell and one female shell, and you can take power from the blue wire.

You can then add a small harness between the dash harness and the gauge. Most of the wires will be straight through, but the wires where you need voltage would also split off to go to your new gauges.

The voltage regulator doesn't have any special properties that would give you a better signal than the two wires I pointed out. As long as the wiring isn't corroded or hacked up, what I pointed out should be fine.

[gundee]

If you wanted, you could give up your clock and install a voltage gauge there using the clock wires.

[HusseinHolland]

9 hours ago, SteveJ said:

Instead of cutting into an existing wire...

Use what's already in the dash. On the clock, there is constant power at the LW (blue/white) wire.

There is switched power at the L (blue) wire on the water temp/oil pressure gauge.

You would need to get two male shells (https://www.hi-1000ec.com/product/1133) and two female shells (https://www.hi-1000ec.com/product/1135) along with male pins (https://www.hi-1000ec.com/product/1662) and female pins (https://www.hi-1000ec.com/product/1663) to go in those shells. If the meter doesn't require constant 12VDC, you only need one male shell and one female shell, and you can take power from the blue wire.

You can then add a small harness between the dash harness and the gauge. Most of the wires will be straight through, but the wires where you need voltage would also split off to go to your new gauges.

The voltage regulator doesn't have any special properties that would give you a better signal than the two wires I pointed out. As long as the wiring isn't corroded or hacked up, what I pointed out should be fine.

Reviewing your idea - I'm not sure adding a (relatively) bulky bridge harness behind the 3 pods make sense. The dash harness is so neat & tidy from the factory, I'm loath to mess with it's layout 🙂

Those wires feed in via one of the C connectors, so it would seem to make more sense to tap or bridge into the harness before it enters the dash. The gauges I'm adding are in the console, not in the dash. I'll look for where the switched blue wire is located in the C connectors, the Voltmeter does not use a constant feed like the Ammeter. 

 

5 hours ago, gundee said:

If you wanted, you could give up your clock and install a voltage gauge there using the clock wires.

Nah, I want to fix the stock clock if possible, I prefer the old analog display clocks. 

[Captain Obvious]

If I'm understanding correctly, you want to put a voltmeter in the console, and you want a switched voltage signal to connect it to? If that's the case, then you could just tie into the blue wire that powers the radio. It's switched, and it's already in the console harness. If all your connectors are clean, it "should" give you an accurate reading of system voltage.

Oh, and BTW, the color wiring diagram you posted above is for the 77. Many (most) systems of the 77 are very similar to the 75, but there may be some differences. I normally would start by looking at that 77 color diagram, but to be sure, you should also double check the old style 75 diagram out of the FSM. Especially wire colors, etc.

[HusseinHolland]

Going to assume the harness with cut blue is the radio harness. Everything else is accounted for, except for the 6 pin plug with small spades

(edit - 3 wire blue variations is power antenna harness)

I don't seem to have anything that connects here, one wire was cut & a fused line was added. Don't know what for. I'm going to assume again it was radio related, as no other accessories have been added to the car by the PO

Edited August 28, 2023 by HusseinHolland
correction

[grannyknot]

I can't believe is has been 10 yrs since I started this thread🥴 

Seems like you have it figured out but you could also go the cigar lighter route and get a couple of USB chargers to boot.

I have one of these in another car and it works well.

 

Edited August 27, 2023 by grannyknot

[SteveJ]

31 minutes ago, grannyknot said:

I can't believe is has been 10 yrs since I started this thread🥴 

Seems like you have it figured out but you could also go the cigar lighter route and get a couple of USB chargers to boot.

I have one of these in another car and it works well.

 

I actually keep one of those handy for when I go over to help someone with his car.

[Captain Obvious]

19 hours ago, HusseinHolland said:

Going to assume the cut harness with 3 (main color) blue is the radio harness. Everything else is accounted for, except the 6 pin plug with small spades

If everything else is accounted for, then I would also assume that 6-position connector is for the radio.

There are five wires leading to the original radio:

• The red/blue and green/white are for the illumination lamp inside the radio.
• The white and white/black go to the speaker, and
• The blue wire is hot when in ACC and ON. Note that power wire goes dead during cranking, so when your voltmeter shuts off while you are running the starter, that's why. 

Also note that same blue wire also supplies power to the rear defogger switch and the antenna switch. So you could verify you've got the right connection by confirming that it's tied to those other two items.

And....... One last thing to talk about. You mentioned earlier about a wide band? That meter system may draw significant power (because of the sensor heater?) and you might not want to pull power for that meter off the same place you put your voltmeter unless you are sure you've got a rock solid clean connection all the way back to the source. I'm thinking the current draw for the sensor may affect the voltage reading. Your voltmeter draw will be negligible, but your wide band may not be.