I think he probable knows that, if he wants real numbers than this thread is trying to help him out in doing so.

 

He probably didn't know how to "calibrate" his OEM voltmeter, but we will let him reply to that.

 

Yes .... Fuse it as close to the battery + (Pos) terminal as you can, 5 amps is planty for a voltmeter.
16 gage wire is fine as well. You can get 5 amp relays but the 30 amp ones are nearly as cheap and no harm .... but look for one with a quenching diode in circuit across terminals 85 / 86. It'll last longer.

http://www.bcae1.com/relays.htm

 

As posted earlier, a 500mA fuse should be used (post #9).


The "quenching diode" protects the coil driving circuit from voltage spikes, it won't help the relay to last longer. The di/dt and coil inductance creates the voltage spikes which will feed back to the coil driving circuit.

 

It's his truck, and he can install a redundant gauge if he wants to. I was just trying to understand why he'd be so concerned about the battery voltage. I have a lot of leftover stuff from other cars that I could probably install in my truck, but I don't see much need for adding equipment which tells me what I already know. If he were already having issues diagnosing a strange electrical issue, then I'd understand.

 

....

 

That all sounds some familiar and I do understand even though I'm not a "radio engineer" (but my Dad was, but I lost him to Multiple Myeloma in 1969) .... but an older radio hobbyist who used to work on the electronic telescopes at Green Bank, W.Va told me they would protect both the relay (he mentioned a "bounce"?)and the electronics on the switching side (in the application which I guess would be the ACC contacts in the ignition switch in this setup?) and kill the mic release "pop" in my "CB Integrator" box I built for my '85 Gold Wing.

I know the energy that is that spike when there's no closed circuit to bleed it or diode / circuit to quench it is the arc that kills switch contacts sortof like a small arc welder.

But now I wonder what the "bounce" was he mentioned?

 

Most switch contacts have a "bounce" that will cause a rapid close-open. But, once again, the clamping diode across the relay coil will keep the high voltage spike from getting to the switch contacts, protecting it.

 

I don't know about your truck, but in mine, the battery gauge always reads exactly in the middle, whether the engine is running or the key is simply on.

I plan on putting a voltmeter and an oil pressure gauge, which I bet you'll also tell me is redundant.

 

You are absolutely correct! I had not tried this on my '05 F-150, but I had tried it on my '99 Ranger, and the voltmeter would change on it. So, I tried it on my F-150, and this is what I got:

1


2


So, my voltmeter "calibration" will not work on a F-150. I knew the oil pressure gauge will show ZERO, or about 1/2 scale, due to the oil pressure sending unit is a normally open switch, that closes with about 7psi of oil pressure. I'm now wondering about the temp gauge.

 

So I guess this forum doesn't have a script to re-size huge pics. Could use one, heh.

The temperature gauge seems to work as expected. Monitoring the ECT PID using Torque and a BT-OBDII adapter, the needle sweep from cold to about half the needle past the center mark matches the ambient to 194f scale in Torque.

I apologize for the "bet you'll tell me it's redundant" remark. I was irritated a bit earlier.

 

The temp gauge seems to sweep from cold to 1/2 scale, but once it reaches 1/2 scale, it doesn't move any more, even idling for awhile with the AC on. Have you checked the ECT PID while idling with the AC on? One thing that tells me the ECT is increasing, the idle speed will increase slightly.

Sorry for the photo size, try these:

 

I hadn't really paid attention to it while idling with the AC on, as I very rarely use AC, even though I'm located in South Texas.

I did notice one day that the needle was completely on the other side of the center mark - Torque read 200f for the coolant temp. I believe it was 107 that day, according to the dash thermometer. This was sitting in traffic at a stop light, once I got on the highway, the temp dropped back down to the normal 194, and the needle went back to it's normal spot.

 

I admin a computer forum and I have one. I've suggested it to the management here but I don't think they care.

 

I believe the stock gauges are dummy gauges.