Hello again FTE!

I feel like I found the answer to this once when I wasn't actually looking for it, but for the life of me cannot find it in the FAQs or How To's. I scored a Bosch triple gauge setup at the pick n pull for $10 to compliment my idiot lights in my '84 F150 and I've gotten everything to work except the voltmeter. I wired It up the suggested way that I found online (engine block ground and a keyed on power source) but that rendered useless results. I wired it to the block to cab ground,and the radio keyed on power. I get no reading until I start the truck, then a sold 12V reading regardless of rpm. I tested voltage across the battery and got 14.5V while the gauge still read 12V so my question is where to wire the power for the gauge so it reads the output of the alternator instead of what is passing through the harness? I have the original Alt setup so I don't know if I should wire to the regulator, or alternator. The whole reason that I snagged this gauge was for an immediate heads up that the alternator failed so that I have time to get it somewhere before the battery completely dies. As always, thank you in advance for any advice!

 

I wired mine to keyed on like you did and than just connected the ground to the dash. On my 79 it was easy as its all metal.
On my 86 with the plastic, I just connected it to where the support arm connects under the dash.
I may have that terminology wrong but just look for the steel arm and take the bolt/screw out that holds the dash in place and use that.
It worked for my digital volt gauge.

 

Did the gauge read properly in your 86? I'm wondering if somehow the ballast resistor in mine got wired to something in the harness causing the constant 12V reading regardless of engine RPM. Or the gauge is just shot, the risk you take grabbing used parts lol. Oh well, let the troubleshooting continue.

 

yes it read properly right away, it is possible that gauge is bad. seems odd it registers the 12v though, I'd think it would just stop working or give a whacky number.
I think one way you can sort of test the gauge is put all electrics on, lights/brights. heater on high, flashers. It should move. or fluctuate even.

 

Get it hooked up to read 12v with the key on. Then turn the engine off, unplug the wiring to the regulator, and then start it and see what the gauge reads. If it reads something less than 12v, then it will serve your purposes.

 

I wired it directly to the alternator to test it with my multimeter as a baseline, and it turns out the gauge is just off by 2 volts. It registered the change in output with rpm as well so I wired it back into the original location. Low and behold it started working properly there as well, just 2 volts low. Considering I paid next to nothing for the three I am cool with that lol. Thanks again for your help!