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Unread 11-01-2013, 12:09 PM   #1
GTNMUDY
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1984 CJ7 
 
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volt meter issues

Need to ask a question regarding the volt meter on a 84 CJ-7.

In some cases while driving my meter will read above 12/13V on the dash gauge. I consider this normal as my alt is putting out 13/14V dc. However sometimes it will read just above 12 and my alt is still putting out 13/14V.

Now when I turn on the lights or turn signals the voltage will drop to 10/11 v on the gauge. If I measure the voltage on the output of the alt it is still above 13Vdc.

If I disconnect the 2 wire plug the voltage output will drop to just above 12V (same as the battery voltage). So this tells me that the alt is working.

When I measure the voltage at the headlight I am getting about 10v dc.

In all cases my alt is putting out 13+ voltage when running. I have measure the resistance from the alt output to the + terminal of the battery, I read 0 ohms. This tells me I'm good there.

If I rev up the engine the voltage does not increase or decrease.

I think I just got a bad voltage gauge.

I want to confirm the following:

Is the voltage gauge connected AFTER the fuseable link or before. If it is connected after the fuseable link I can see why their may be a different (lower) voltage reading on the gauge.

My manual does not show a complete wire schematic, only the testing of the items and it doesnt state if there is a fuseable link in the line.

FYI, I did a SBC swap 20 yrs ago, so the wiring for the engine to the elect system is not Jeep. But since my SBC is not ECU controlled it was very simple to get it hooked up.

Larry

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Unread 11-01-2013, 12:33 PM   #2
texasdave
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From the alternator back you have a fusible link prior to going to the gauge. You may have some corrosion on the gauge terminals and cleaning would help also your ground may not be making good contact all the time. Its 29 years old probably close enough.
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Unread 11-01-2013, 12:37 PM   #3
MoneypitCJ5
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The voltmeter is connected downstream of every electrical load, so as you turn things on and off the voltage on the meter WILL change. It actually gets its power from the ignition switch instead of the battery so the number on the gauge is total system voltage rather than battery voltage or alternator output.

Adding grounds will help to stabilize the system voltage but it will rarely be steady. You honestly can never have too many.
Also, if you use a small gauge wire for the "charging" wire off the alternator it will cause problems too. I think 10 GA is factory, although 8 GA is better.

This is my experience with a factory Motorcraft alternator with an output of ~45 amps.
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Unread 11-01-2013, 01:17 PM   #4
GTNMUDY
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I agree I know there is a fuselink in line with the + side of the starter that goes to everything else. (had to replace it once)

I do have what looks like 10 gauge wire coming off the alt and to the starter + side and then to my battery with the heavier gauge wire.

This is not a stock alt, I replaced the field coils with a 80 Amp some time ago.

I was going to check the connections on the voltmeter, but I'm not to keen about pulling the radio and sound system wires I got tucked up under the panel

I think I will put a digital meter in and wire up to the battery. I want to know what my alt and battery are doing.

larry
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Unread 11-01-2013, 01:37 PM   #5
MoneypitCJ5
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I can't say that I blame you on that one. The factory unit is more or less there for appearances rather than giving you useful information.
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Unread 11-01-2013, 02:04 PM   #6
JeepHammer
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Money is right on this, I've had to deal with this complaint more times than I can count...

The issue is...
There is a single 10 Ga. wire (With fusible link) feeding the fuse block, the fuse block splits up the power for lights, radio, ect.
And your volt gauge is at the end of all those electrical loads.

You aren't reading 'Battery' voltage, you are reading 'Line' voltage after everything in the fuse block AND the headlights have sucked on that single 10 Ga. line from the battery cable/starter relay.

With all those electrical loads BEFORE the volt gauge, it's going to show lower than battery voltage no matter what you do.

You *CAN* wire it so it reads battery voltage, or output from the alternator...
To do that is LONG AND COMPLICATED, involves switches and relays to supply battery voltage to the gauge,
And it all has to be switched 'OFF' when the engine isn't running or it will drain the battery,
So it's really not worth the time/effort to do so.

A 'Noid' light, usually an LED or small bulb, is pretty easy to wire into the system to tell you if the alternator stops charging,
And/Or a separate volt gauge for the battery can be installed, but it's much more difficult than a noid or 'idiot' light...
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Unread 11-01-2013, 02:20 PM   #7
MoneypitCJ5
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Hammer, could you instead use the voltmeter feed off the ignition switch to power a relay wired directly to battery?
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Unread 11-01-2013, 02:32 PM   #8
JeepHammer
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Yup, you could... But it will probably require a diode to keep the relay from back-feeding and running the battery down, plus it will take wiring for relay, wires both in and out of the voltgauge, ect.
In most cases, not worth the trouble once you know what's causing the low voltage reading.
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Unread 11-01-2013, 02:47 PM   #9
MoneypitCJ5
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I hate to hijack a thread, but do you have any suggestions as the best way to update and upgrade the wiring harness as a whole? I'm having trouble choosing a direction to go. Any help would be awesome!
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Unread 11-02-2013, 03:11 AM   #10
John Strenk
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You mean like what company you should purchase a wiring harness from?
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Unread 11-02-2013, 08:51 AM   #11
GTNMUDY
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Thanks for the feedback HAMMER.

I agree and understand what your talking about. I didnt think about the constant drain on the battery if I hook the meter directly to it.

I was looking at a digital volt meter. I know the drain on that is less than the stock volt meter.

I might just look at a relay operation for the volt meter. Wont take much.

Larry
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Unread 11-02-2013, 10:55 AM   #12
JeepHammer
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There are some other companies that sell wiring harness kits, other than PAINLESS...

What I usually do is find a small donor vehicle at the salvage yard, one with a covered fuse block under the hood, one with standard relays built into the fuse block...

That way, the things I need relays for, Headlights, manifold heater, ect. have relays built into a water resistant, if not water tight case and work from there.
There really is no reason for EVERYTHING to go into the cockpit and half back out of the cockpit, so doing it under the hood makes sense to me.
Standard size fuses (not the glass type), Relays, usually has fairly heavy gauge wire since people think they have to have power seats, power mirrors, power nose pickers these days, so there is plenty of circuits for off road lights, electrical accessories, ect.

The only issue I have with doing this is...
You can't 'Scab' it into the existing harness, you will have to start from scratch, which scares the crap out of most people...

Some of the junk yard finds have sealing boots for the wiring entering and exiting it, and if you look around, they come in all shapes and sizes...

For those of you that have an allergy to anything 'Used' or from a 'Junk Yard', there are fuse blocks on the internet you can start with, and some are pre-marked for circuits and/or have partial circuits hooked up when you get them.

Personally, for about $50 I can get the terminal ends, boots/seals and other small parts that allow me to make custom wires that snap right into the fuse block,
And I can have EXACTLY what I want instead of having to scab onto the old harness.
Since I already know I'm going to use better components than the factory did, I know I'm coming out in the long run...

Instead of splicing a wire in the middle somewhere to scab something in, I just put two wires in the connector at the fuse block, or at termination, whichever is more convenient for the second hook up, and that way there are no breaks in the wire insulation...
And I don't use the official 'AMC Duct Tape' at splice connections...

Since about everything is sealed up and away from bugs, rot, corrosion, water or whatever, it's going to out last me at my age...

DO NOT forget to work up an ACCURATE WIRING DIAGRAM AND LABEL WIRES!
Don't be the guy that buys three rolls of wire and everything on the vehicle is one of those three colors with no labels, and no wiring diagram to tell you where anything comes from/goes to!

I've tried to post up some of the basics of wiring you will find on a CJ, but you will always have to root around, do searches to find some of the connectors, wire colors/color coding, ect.
But it's worth the hunt when you have EXACTLY what you wanted and everything works EVERY TIME!
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Unread 11-02-2013, 11:00 AM   #13
JeepHammer
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Quote:
Originally Posted by GTNMUDY View Post
Thanks for the feedback HAMMER.

I agree and understand what your talking about. I didnt think about the constant drain on the battery if I hook the meter directly to it.

I was looking at a digital volt meter. I know the drain on that is less than the stock volt meter.

I might just look at a relay operation for the volt meter. Wont take much.

Larry
I'm trying to remember where I saw it... I think Radio Shack... A large number display in a frame, two wire hookup.
I used one when building an alternator test bench a few years back. Bezel was already installed, about 3/4" by 1.5", Zero to about 99 volts, with a 1/10 volt behind the decimal point.
Root around Radio Shack website to see if it's still available...
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Unread 11-02-2013, 11:11 AM   #14
RenoF250
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I disagree that it is worthless. My battery clamp fell off last time I Was out and the battery bounced down near the engine and the + terminal came off. The Jeep started to run like crap but the VM let me know there was really a problem when it pegged.
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Unread 11-02-2013, 12:28 PM   #15
dg6772
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You can solve some of the jumping around. My 86 was doing the same thing plus the light wasn't working. I found it was a ground, I added a ground to the meter the light came on and the meter started to work more as it should. Still moves around some ( not like before ), and still not real accurate,but way better than it was. It operates between 13 & 14 volts all the time now. Even with everything on.....

Dave in Muskegon
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