Problem at the wiring shop

[47heaven]

Got a call today from the guy that's rewiring my car and he told me that with the new harness the amps meter wont work because it's now running on volts???? He said I need to get a volt meter guage, which would change the instrument board. Have any of you guys run into this problem when rewiring and switching from 6 to 12 volt?

[david lazarus]

Had same issue with my '38...decided that the Amp meter didn't need to work, and with the needle sitting in the middle (at rest) did not look out of place. What I DID put in was a volt meter, as this tells me amost everything I need to know...like is my battery at full charge...if not or if charge is falling I can look into it. Even better with a Volt meter if you have a fault and your charge is dropping you have time to shut off unnecessary electrics and limp to a garage/home.

[Norm's Coupe]

Darin,

Send Don Coatney a private message. He switched to 12 volts on his P15 and I believe he's still running his original amp meter, and it works. Don't think he put in a new wiring harness though. Also, Ed Gross is running 12 volts in his P15 with his big V8 and still using the original dash gauges. I believe he has a new wiring harness in his.

[jd52cranbrook]

I changed over my 52 with no problems at all using the same amp meter. Except I had to reverse polarity as it is neg ground now.

[John Mulders]

That was made clear to me by the guys in the forum.

The amp meter doesn't care about the Volts.

John

[Plymouthy Adams]

Now running on volts...how stupid is this..what was it running on before if not volts...SORRY..granted the newer cars are running voltmeters due to the size of the wire they are using and the number of high current circuits. If your car is not loaded down with AC, mega watt amps, power widnows, power seats etc..then there is no need to by pass and not use your current amp meter. Sorry guy but they are not doing you any favors wiring your car and asking you to install a voltmeter. Only thing that comes to mind is that they are installing some off the shelf fit anything x-amout of circuits generic harness...even with that you can still run your amp guage if they really knew what they were doing...something abou this stinks in my opinion. Your car should not have any off the wall gauge stuck willy nilly about the dash.

[Reg Evans]

I'm another one using my amp gauge on a 6 to 12 volt conversion. It's been working fine for more than 10 years.

[Don Coatney]

Got a call today from the guy that's rewiring my car and he told me that with the new harness the amps meter wont work because it's now running on volts???? He said I need to get a volt meter guage' date=' which would change the instrument board. Have any of you guys run into this problem when rewiring and switching from 6 to 12 volt?[/quote']

I think I would either do the re-wire job myself or find another shop that knows what they are doing. The attached schematic is very basic but shows how an ammeter can be wired into a circuit and voltage has nothing to do with it. The important thing is to follow the wire size guidelines.

The comment "the amps meter wont work because it's now running on volts" makes me laugh.

[TodFitch]

My guess is they are installing a off the shelf harness that has no provision for a high current wire from the battery/starter to everything else that the ammeter can be spliced into. Probably just have a single low current line run from someplace like the ignition switch that they can hang a voltmeter onto.

In the best of all possible worlds you would have both as they tell you slightly different things about the health of your electrical system. But if you can only have one, I'd rather have an ammeter as it gives a better feeling about what is happening to the battery.

I have rewired cars three times. Twice using a factory duplicate from a reliable vendor like YnZ's or Harnesses Unlimited and once making up the harness myself. Doing it yourself is cheaper but takes a lot longer and it is hard to get as professional looking a job.

Having it done to non-factory specifications by someone else who is making wild assumptions about what you want strikes me as being dodgy. I'd rather do it myself, especially if I wanted to deviate from stock.

[Plymouthy Adams]

What we have here...and mind you this is just a WAG. The wiring schematic in the KIT does not show a Ammeter and just a voltmeter therefore leaving the installer way out in left field if he is just that, an installer without any knowledge of how the ammeter works. Ths installation of a shunt across the meter equal in resistance to the meters internal resistance will effective divide the indicated current in half..example is, where the meter will now show 10 amps, acutal is 20 because the other 10 is dropped across the shunt. Knowing the internal reisistance is paramount, knowing how to measure this without damage to the meter is also a must. Ohms law comes into play..running 12 volt system pretty much will make your shunt 12 guage wire...length of the wire is the resistance...this can be done precise with your meter and voltage or close enough for horse shoes working with a known current draw. This is best done on the bench. Now if you choose to install a shunt...DO NOT forget about meter protection...to prevent damage should should the shunt fail, install an inline fuse rated to the indicated value of your ammeter..that way if failure in the shunt should occur, the full current will be felt on the single line and will open the fuse and protect the meter and wiring harness itself.

This is the route I intend to take with my car..it will have all power options except power seats...power up for sure..but power up safely please.

[blueskies]

I'm using my stock amp guage with my 12v neg ground setup.

I'm also using a new fuseblock and wiring from EZ-Wiring.

The heavy guage main power wire that runs to the fuse block should run to the amp guage first, and then to the fuse block. The only difference, as already mentioned in this thread, is that the connections to the amp guage must be reversed, or the guage will read backwards because it was originally designed for a positive ground system.

There's no reason not to use the amp guage you already have. Of course, it tells you different information than a volt meter, but so what? It will tell you if the system is charging or discharging, just like it did for decades before...

Pete

[Plymouthy Adams]

Basically it is like I said before..if he is not installing a bunch of energy draining circuit that will be working all at the same time..stock is adequate and going to 12 volts is an added plus for you current meter..I contend the shop does not know how to wire the main feed through the meter...no one else is having this problem !!!!!!!!!!!!!!

[teardrop puller]

If your installer can not add larger wire for the amp meter, or the kit has the correct wire and he did not know it, I would get rid of him.

The amp meter only records what is going and coming from the battery. If you have things that use power when the car is running, then nothing will show on the amp meter.

kai

[bob westphal]

Where did you get the new wiring loom anyway? Did you get an original replacement? An original wire loom will have adequate wire sizes. Remember guys, this isn't rocket science! The amp meter doesn't care how many volts are going through it! It measures only amperes alias current flow! The main thing you need to worry about is did the new loom come with #10 or 12ga. wire for the amp gauge or what the installer says volt meter? If it didn't you have the wrong loom. You will need to replace the smaller wires with the correct wires. It ain't hard guys!! Kai is right you may have the wrong guy working on your car.

[Lou Earle]

Look it is real simple-

Either the person is lying to you and trying to get more money out of you or

They are dumber than spare tires when it comes to electrical.

Either way I would not have them put new air in the amp meter or voltmeter !!!!

Lou

[Normspeed]

I think Blueskies hit it. If the shop is using an aftermarket harness, it probably isn't set up for everything except the starter to pass first through the ammeter. Pete's solution should fix that easily.

[Plymouthy Adams]

The one big problem some people have when converting from generator to alternator and the higher ouput the alternator is capable of, is assuming that that the current form a 60 amp alternator is always flowing 60 amps..and because of this the current current meter (like that double) is rated less than the output of the new device. The alternator can put out more current at a lower rpm than the generator..the biggest advantage...especially when running items like AC etc. They are quick to recover..high amp at lower rpm equals short recovery time..also keep in mind that the car's charging system is not designed to charge batteries, it is designed to maintain that charge. The voltmeter is of choice in modern cars for its ability to monitor your system with no current flow through it own movement..wire size is smaller. Cars today are fed through power distribution centers from multiple battery taps and protected cirucits with fuseible link, power up relays etc etc..this take all that away from the ignition switch also..as it now, it is used to power up relays coils, very low current compared to yesteryear thus giving the car's electrical system a better chance to operate with less chance of melt down. Rarely have I seen a car's eletrical system load the fields of the alternator to draw in excess of 60 percent rating of the dynamo...above this and the chance of diode damage is greatly increased...anyone testing a circuit above this rating is not doing you or your car any service..instead the possibility of damage during this one test is almost assured..

[greg g]

I will admit right off the bat I do not know much about electricity. I do know that electrical leaks a probably much more dangerous than plumbing leaks, but other wise the systems are similar. Measurements of usage are even similar. pressure (volts) and flow (current). I for one think the Ammeter is a much better indicator of what is happening to your electrical system than volts. I had a 63 something or other with an alternator and an ammeter. It worked just fine on volts........

The simplified way to wire a one wire alternator is to connect the output to the wire that was attached to the BAT terminal of the the voltage regulator, this wire goes to the Ammeter, then back to the battery. The only other thing that needs to be changed it that the wires on the posts of the meter need to be switched to account for the new negative grounding scheme. So have these guys arrested for failure to follow OHM's law. And I wouldn't be posting no bail.

[Furylee2]

Well we’re on the subject, a fellow Prairie Region member and I went and looked at a 49 Special Deluxe for sale last weekend. The owner passed away, and his wife took us over to look at the car. After airing up the tires (it hadn’t be started since last summer) and pushing it out to jump start it we finally got it started and took it for a drive. The owner converted it to a 6V negative ground alternator, and the gas gage was rapidly jumping from empty to full, back and forth. Is this related to the fact he converted it to negative ground? Lee

[Norm's Coupe]

Well we’re on the subject, a fellow Prairie Region member and I went and looked at a 49 Special Deluxe for sale last weekend. The owner passed away, and his wife took us over to look at the car. After airing up the tires (it hadn’t be started since last summer) and pushing it out to jump start it we finally got it started and took it for a drive. The owner converted it to a 6V negative ground alternator, and the gas gage was rapidly jumping from empty to full, back and forth. Is this related to the fact he converted it to negative ground? Lee

Lee, converting to negative ground or to 12 volt would not cause that problem. That is probably caused by a bad sending unit, dash gauge or a bad wire grounding (shorting) out.

[47heaven]

Thanks to you guys, my wiring guy has decided to just go ahead and connect the ammeter and use it as described in your posts. I made a copy of them and had him read what was explained and he realized that it would work, of course.

Anyway, thanks for helping out here. It saved me from having to have a conversion done.

[grey beard]

I did not realize until I read this thread and saw the schematic posted by Don C that car and truck schematics are almost identical, although come to think about it, there would be no logical reason for them to be much different other than the extra accessories on a car, he said in one long run-on sentence.

I have just finished making up a new harness for my B1B - took about six hours, half of which was devoted to soldering on terminal ends. Thsee are easy to make. The drawings with all the dimensions are in the PIlotr's Knowledge section of this forum. Don't know if dimensions are different for cars, but I think only the rear body harness will be different.

Having been through the process, I can promise you all that there is NO reason (other than owner's choice) for using a voltmeter. They're nice to have and by all means get one if they blow your skirt up, but the ammeter will always work - pos or neg ground, six or twelve volts. If you reverse polarity, just reverse the ammeter leads - hardly rocquetrte science.

AND, by the bye, when one switches from six to twelve volts, the current (or amps) going through the circuit is only half that of the original six volt system. This means that if your new harness was made for six volts, it is TWICE as stout as needed for 12 volts. The reason for the switch to 12 volts long ago was to save wire size, battery cable size and swirtch wear, because only half the amperage is now flowing in the circuits. Of course 12 volt systems do tend to (ahemmm) crank a tad faster than six . . . . .

[martybose]

(snip)

AND, by the bye, when one switches from six to twelve volts, the current (or amps) going through the circuit is only half that of the original six volt system. This means that if your new harness was made for six volts, it is TWICE as stout as needed for 12 volts. The reason for the switch to 12 volts long ago was to save wire size, battery cable size and swirtch wear, because only half the amperage is now flowing in the circuits. Of course 12 volt systems do tend to (ahemmm) crank a tad faster than six . . . . .

Technically, this statement is true on an item-by-item basis. However, most 12V systems also tend to use more modern, higher amperage charging devices (ie alternators rated at 60 amps or more), so you will see higher amperages when the battery is initially charging after starting the engine. My amp gauge usually pegs for a couple of seconds before it drops back in range.

Marty

[DutchEdwin]

Did my rewiring with the scheme on my lap inside the car. I did change the wires one by one, putting in the new one when I took out the old one. So this way no mistake could be made. Took me (by easy doing) 1 week.

For 6V, I checked the wire sizes with the high standards (UL-listing) they use in office machines. I did find out that UL prescribes thicker wires for the high currents then used in the goodolday's. I went to twice the thickness of the wires, using modern plastic wires for safety reasons. On the main wire from the battery to the car inside I used 6 square wire (that's metric). The original wire was not allowed by UL-standard (wonder if much cars did burn because of overheating of the wires). Because copper will corrode over time the resistance will grow, so also the heat in the wire.

Second, 6V will give more lost of volts when you get further away from your battery then a 12V system. Going to the rear of the car, what will be left when it reaches the bulb?

So I took twice as thicker then Walter put in. Also running return wires, so the return current does not run through rusty metal joints.

My 2 cents.

[bob_amos]

My goodness, This is so simple. The amp meter will work on 12 volts. All it does is register the current flow. Tell the guy to just wire in some additional wiring that will handle the load. Connect it to the meter and read the flow. You said this was at the wiring shop? Or was it just a mechanic that is wiring it for you? Any electrical tach should know how to handle this.