Question about the Marauder voltmeter

[CrownVic75]

On a true Marauder; how many volts does the gauge read?


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[SteelQualityMan]

When-starting, running, hot day, cold day, a/c compressor clutch in / out, etc?

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[fastblackmerc]

Alternator output should be between 13.8 & 14.2 volts.

"While maximum alternator output is dependent on the rotational speed of the input shaft, the actual output is load-dependent. That basically means that an alternator will never generate more current than is called for by the momentary demands of the electrical system.

What that means, in the real world, is that while an underpowered alternator can cause problems by not meeting the needs of your electrical system, a substantially overpowered alternator represents a lot of wasted potential. For instance, a high output alternator might be capable of putting out upwards of 300A, but it won’t actually provide more amperage than a stock 80A unit if that’s all the electrical system ever tries to draw."

[CrownVic75]

Thanks for the info.
But, or Butthead, it finally dawned on me that the voltmeter in the center console pod is reading the battery voltage (which should/will always be 12.5+ volts),not the charging voltage. What a dummy I can be sometimes. So I'm going to connect it to the alternator through a relay.

[SteelQualityMan]

Thanks for the info.
But, or Butthead, it finally dawned on me that the voltmeter in the center console pod is reading the battery voltage (which should/will always be 12.5+ volts),not the charging voltage. What a dummy I can be sometimes. So I'm going to connect it to the alternator through a relay.In theory, the only difference between the voltage measured at the battery and the voltage measured at the alternator is due to the resistance of the cable connecting the alternator output to the battery. Batteries are not constant voltage devices; the voltage at the terminals will vary depending on a number of factors such as battery condition, temperature, and load.

There is a mod available to upgrade the cable from alternator to battery and improve some of the ground cables. Someone here with a better memory than mine can post the name of that mod or a link to it.

Why do you need a relay to connect a battery to a voltmeter? Just curious.

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[justbob]

Thanks for the info.
But, or Butthead, it finally dawned on me that the voltmeter in the center console pod is reading the battery voltage (which should/will always be 12.5+ volts),not the charging voltage. What a dummy I can be sometimes. So I'm going to connect it to the alternator through a relay.



What?? If you’re only seeing 12.5 then you have other issues. The only way that gauge would ever read just battery voltage is if you disconnected the alternator.

Why else would everyone else’s car register high 13’s to low 14’s with only a 12V battery?


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[CrownVic75]

Why do you need a relay to connect a battery to a voltmeter? Just curious.

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Even though the voltmeter doesn't draw much current (not a concern) if I connect it straight to the battery it would be "on" all the time, even with the key off. So I figured if I put a relay between the voltmeter and the battery and connect the relay "pick coil" to a "Voltage in Run or Acc." fuse/connection, the voltmeter would only be active when the key is on.

My theory is (as someone else stated) that the alternator is the "heart" of the car's electrical system. The battery is only used to start the engine. I thought it might be more advantageous to monitor the alternator.

I'm in my 70s now, but back in the day (when I was a teenager working on hot rods) most cars had ammeters, not voltmeters. One could tell if the "generator" (before alternators) was charging the battery and running the car. High current or no current draw, meant problems. During the middle to late 1960s manufacturers changed to alternators and put in a voltmeter.



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[CrownVic75]

What?? If you’re only seeing 12.5 then you have other issues. The only way that gauge would ever read just battery voltage is if you disconnected the alternator.

Why else would everyone else’s car register high 13’s to low 14’s with only a 12V battery?


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Well, my problem here is that I allowed an idiot, at a "Custom Cars" shop, to install the Marauder instrument cluster and the two gauge pod. I've already documented that mistake in another post. As of yet, I have not had time to trace down how he connected the voltmeter. But IMO he connected the voltmeter to the wrong voltage source. (It's supposed to be connected to the center console's power lead.) That's why I'm asking these stupid questions.

Last week I installed a new battery and swapped the 4g alternator for a 6g, 200amp, alternator, yet the voltmeter inside the car always reads less than 13 volts. But a multimeter at the battery reads 13.9-14.2 volts. Thus my concerns.


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[RF Overlord]

I don't think the OEM voltmeter is highly accurate, but it should be reasonably close.

I think the point you may be missing is that the alternator is connected directly to the battery (via a couple of fusible links) so no matter where your ersatz technician connected the voltmeter, it should still track. It'll read a little less with the engine off and maybe a volt to a volt and a half more with the engine running. If it's just stting there reading the same voltage all the time, it's defective.

[SteelQualityMan]

Even though the voltmeter doesn't draw much current (not a concern) if I connect it straight to the battery it would be "on" all the time, even with the key off. So I figured if I put a relay between the voltmeter and the battery and connect the relay "pick coil" to a "Voltage in Run or Acc." fuse/connection, the voltmeter would only be active when the key is on.

My theory is (as someone else stated) that the alternator is the "heart" of the car's electrical system. The battery is only used to start the engine. I thought it might be more advantageous to monitor the alternator.

I'm in my 70s now, but back in the day (when I was a teenager working on hot rods) most cars had ammeters, not voltmeters. One could tell if the "generator" (before alternators) was charging the battery and running the car. High current or no current draw, meant problems. During the middle to late 1960s manufacturers changed to alternators and put in a voltmeter.



.Alternator output ==battery input. Any significant difference would be a defective cable or bad connections. Disconnect the battery cable and check it with an ohmmeter. It should read essentially a dead short. Do the same with the negative cable.

I understand your explanation about the relay, but I would be willing to bet that the receiver circuit for remote door and trunk unlock draws more current than a quality voltmeter. If you are in doubt about the condition of the under hood or under dash wiring then run a wire directly to the battery positive stud on the side of the under hood fuse box. That is what I use for any voltage testing.

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[CrownVic75]

SteelQualityMan (https://www.mercurymarauder.net/forums/member.php?u=10741)

If it's wired to the BJB side stud is't the voltmeter reading all the time?


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[justbob]

Pull the gauge pod, test wiring with a multimeter, rule out bad gauge. If gauge is good, cut the positive wire and heat shrink the end. Re route positive wire to cigar lighter. Done.

Chances are that is what he already tied into because it is the simplest route and your gauge is junk. A quick multimeter test is quicker than re wiring, adding relays, or starting threads IMO.

Just verify your actual voltage at the gauge and the cigar lighter before further diagnosing.

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