amp meter wiring

[knighthawk]

I am using a newer wiring harness and componants ( '85 ) in the '48, problem is , the gauges are completely different, ( wired with 20 ga. wires) What is the wiring layout for the '48 amp meter ?

[BobT-47P15]

Here's a P15 wiring diagram from the repair manual. And also a link to the

picture in my PhotoBucket album, if that would be any better to read.

http://smg.photobucket.com/albums/v96/BobT3/Parts%20Book%20-%20Other%20Literature/?action=view&current=100_2970-1.jpg

edit: Oops, I just remembered your car is a Dodge D24.......maybe they are similar.

[greg g]

well if you are still 6V, the 20 gauge stuff will have a lifespan of about 30 seconds. Essentially the current from the generator passes through the VR out the batt post through the Ammeter and back to the battery via the front side post of the solenoid.

If you are running an alternator, you can connect the output wire of the alt to the wire that was connected to the battery post of the old VR then throught he Ammeter and back out to the battery. Eiter vial teh solenoid post or directly to the battery post Pos if neg ground Neg if pos ground.

The current travels through the meter.

[knighthawk]

so........the original ampmeter will handle the full 100(?) amps from the '85 12 volt alternator ?

[HughForrest]

Your Alt rarely puts out its full capacity. I'm running both my cars on 12 volt 60something amp alts with original amp gauges with no trouble. I don't think the amp gauge wire is 20 ga though. 10 ga is more like it. That is what was in my harness (EZ Wire brand).

[bob_amos]

You didn't say what the harness was from but at that time most manufacturers were using a shunted ammeter system. This wiring did not carry the full load and that 20 gauge wiring would indicate that. In a shunt wired system only a small portion of the current would flow to the ammeter while the rest went directly to its destination. They would tap into the main harness at two locations to achieve this. Looks like this is what you have. Since the original gauge was designed to real the full flow and not a portion of it, you probably will not have an accurate reading. (If it'll read at all.)

[knighthawk]

thats proabley true... the '85 gauges have enough electronic crap and printed circuts in them it fill a transistor radio ! So, what do I do now ? I don't have access to shunts, resistors, or even know what they are ??

[bob_amos]

Best thing to do for the ammeter is to hard wire in the proper leads to handle the current. Just overlay this onto the exsisting late model harness you are using. But, I am not sure that using any late model harness is best. A proper built harness for all your needs would be best. Costly but best.

[builtfercomfort]

As I understand things (as usual, someone please correct me if I'm wrong!) , the fat wire from the alternator to the battery goes to the ammeter instead, and the wire goes from there to the battery.

All charging current thus flows thru the ammeter. That's all there is to it. I had an aftermarket one once wired backwards - but it worked.

[Plymouthy Adams]

the wiring for the amp guage on any mopar vehicle during that era (85) will find only a sampling of the current through a shunt...full actual current is not drawn through the meter...

You original ampmeter of 48 could be what? 40-50 amps..though it may not be everytime you run it pulls that much..odds are with lights, possible electric fan, AC clutch and blower, wipers etc etc a low battery could pull upward of 40 amps for a short period..this would taped rather fast. If you wish to run the stock amp guage..there is two ways to do this...parallel a second meter of same milliamp resistance or run a heavy 8 guage wire with the internal resistance equal to the guage parallel to the amp meter...this will split the amp load so that if in fact your guage shows 20 amp charge..in actuality you are pumping 40...

[Guest rockabillybassman]

You should not really run the output of an alternator thru the amp gauge. It'll be OK most of the time, but if you have a "left the lights on" situation and the alternator starts cranking out big amps, you've suddenly got up to 100 amps thru your dash wiring, and amp gauges were never designed to handle that. There have been many cases of them catching fire.... not a good look!

When I put an alt in my car, I disconnected the gauge and installed an idiot light.

[martybose]

Maybe it depends on how big an alternator you have. Mine is an 80 amp, and rarely pegs the ammeter more than a second or two.

Marty

[builtfercomfort]

I'm about to wire my 39 for 12v, and want to keep the ammeter - and so I am reading this with some interest. What do you think the resistance of the internal ammeter is? And how many watts would I need on a such a resistor?

[Plymouthy Adams]

first is that you will not be finding a resistor per say..the rating will be in milliohms..sorta like a steel bar...I measured mine for the 47 Dodge...calculating the amount of wire needed to match that resistance would be a lengthy run..so I have opted for running a parallel amp gauge..in reality...you could mount one under the hood at the same time you have the one inside...(parallel these)..that way you get 1/2 reading on each gauge..

[builtfercomfort]

I read this thread at the hotrodders.com forum - I'm mostly convinced to try a voltmeter, though I prefer an ammeter.

The drawbacks they mention are:

1. You have a large, always-hot wire going into your dash. If you touch it with something grounded (like your hand) it will send power through things that should not have power through them (like your hand).

2. If using the old gauge, sending all your car current through this 70-year-old gauge.

3. If using a new gauge, it probably has a shunt. These shunts may get hot/old and die, and because you are sending all your current through the ammeter, your car stops.

But I'm already planning on taking apart my dash and replacing the oil pressure & oil temp gauges with the guts from new 12v ones, (hopefully using the old needles) and perhaps replace the fuel gauge too (I first need to see how the stock one works with my new sender). So a modern, tiny ammeter that I trusted would be good for aesthetics - I'd put it in place of my stock one.

I could put a voltmeter in the same area and work on the lettering, or just put tiny dots in at the calibrated points and leave it saying 'amps' but actually measure 'volts' - but I don't like that idea much.

I don't have the skill needed to re-letter the gauge area to match, and don't want to pay the hundreds to get someone to do it - does anyone know of a source of old-timey decals for gauge lettering? I'd have to do all to match, but that would be okay with me.

But since reading the thread linked above, I'm hemming and hawing... Hmmm....

[knighthawk]

I'm kinda leaning towards the voltmeter myself, any suggestions as how to maybe change the guts of the ammmeter ?

[HughForrest]

Volt and amp meters tell you different things about your charging system. All my reading says a failed amp meter will not set your car on fire. If it fails it'll fail like it was a fuse and just cut the power through it.

If you have a wire rub through it's insulation and arc to your firewall or dash that is not the fault of your ammeter.

[builtfercomfort]

I'm thinking of putting new graphics on my gauges anyway because the old decals are falling apart. Thus I can put 'volts' where 'amps' used to be and change the numbers as needed.

I'm looking at print-it-yourself decals and rub-on letters from this place- I'm hoping they can be made to work in an auto environment. The rub-on type can be printed on a laser printer, while the water-slide kind use ink-jet printers, and ink-jet ink often fades in sunlight. So it's still in research right now.

I need to re-do my gauges (mine are bubbled and looking poorly) and I'm hoping this will work for me - assuming I can find the right font and get these decals to work. There are zillions of free fonts, one should be close enough for me.

A restored version of my dash looks like the attached file - I don't need to match the font exactly if I replace everything.