amp gauge: a right and wrong way

Hey guys...

This may sound like a VERY silly question... But, when it comes to our era amp gauges, this case a 67 Plymouth, is there a proper "left" and "right" post when attaching the red and black wires? I would think the gauge just senses the current regardless of the way it is traveling through it... I could be wrong...

I went to hook up the battery after reinstalling the instrument cluster and dang, the fusible link went up and smoke. Smoke even came out of the ground point on the radiator core support where the negative battery cable body ground attaches... Never saw that one before... I quickly removed the positive cable from the battery and checked the wiring under the dash at the bulkhead connector and outside on the firewall. The only wire that seems to have been affected is the fusible link... Whew....

Not sure about a 67, but I just did a dash swap on my cuda and underneath the studs, it was stamped on the back showing which wire went to which stud. By reversing the wiring it may affect the gauge reading as to whether it is drawing current or charging. Not sure though.

If you run a positive wire to a ground stud, chaos will ensue.

Here is the back of a 1970 Duster cluster just so you can see how the newer ones were marked, check yours for sure!

There is no ground side on the amp gauge. It is just in and out. That is why when you bypass the gauge you just hook both wires to one terminal or together. If you reverse the wires the gauge just reads backwards. It sounds like you have a dead short somewhere.

Sounds like you screwed the pooch, while the gauge is designed to work in series, there is correct manner in which the current flows thru the gauge, should be marked with "red", or "S" on the primary terminal of the gauge to receive the red wire, black/dark blue on the other terminal

FYI, replace those "paper" mounting insulators on the posts with some nylon washers...make sure your isolating the studs properly in the dash cluster

Yeap. That is what I was afraid of. Wondering if the starter relay could cause it. Otherwise, I am going to pull the cluster out again and see if the amp gauge shifted some how on the frame and touching it.

Hey Mike.
On the back of this GTX's circuit board there isn't any markings, either from not having them to begin with or age and many hands touching it over time. Done plenty of Rallye clusters and they do have a RED marking on the housing. Not so on this GTX. Like your idea on the nylon washers.

The right way is not have the entire electrical circuit passing through a gauge.

Understood... But the owner can't get the conversion system.... I have done it on pretty much all my cars over the last decade...

Well Hell..... There is a "RED" stamped in the printed circuit board.. I think I had them backwards..... Live and learn...

It doesn't. Only the battery circuit.

But if they were backward, all it would do is show current going in the wrong direction. In other words it would show charging the battery when it was discharging.

Definately a major short downstream of the link.
Fusible Link in Charging Systems with Ammeters
The advantage of the original layout is the one link protects everything from the battery grounding. This means the alternaotr output wire can be run to the distribution points without additional fusible links - which of course add resistance under high draw situations.

I would NOT use nylon for a washer. Nylon can soften when warmed and then the nut will be loose and the connection isn't secure. Resistance goes up and then there will be a problem at the connection.

Use a material that does not flow. A fiber washer is good, and there a plastics that are acceptable -best if thermosetting, but in any event not something to risk with a maybe OK. Something from an electical supply house should have the info needed.

What Mattax said, you have a dead short somewhere (likely at the ammeter terminals to ground) & if you have the red/black wires/terminals on the wrong ammeter posts it will just read backwards (but no harm/no foul) on that issue anyhow.

I found an extra original fusible link ( i'm glad I keep my old harnesses )... I replaced it, and with the instrument cluster removed, I joined the black and red amp gauge leads... Placed the positive back on the battery and no harm... Used my screw driver to test the starter relay and it worked just fine.... So, something is going on with the cluster.. I have a good insulator between the gauge and housing, so I'm not sure.. The gauge doesn't appear damaged.. It is a pretty simple design mechanically...

I'd dig into the gauge when you can & find where it is dead shorted to the (ammeter) case.

From what has been described, if there was a short in the ammeter, there should be evidence. It should show signs of heat and smell of burnt metal and plastic. Shouldn't have to open it to determine if its OK.

I say this because the fusible link went fast, and it was enough current that even the body ground couldn't handle it. Of course if the body ground wasn't a great connection to begin with, then that does't means so much.

Some place the hot wire had pretty good contact with the body. That is, assuming the engine block connection direct to the battery negative was good.

I know its PIA, but it would be well worthwhile removing the bulkhead disconnect and check the charging wire terminals, esperically at the crimps. If they show signs of overheating, repair depending on condition.

(also, if the foam seal is real crumbling, Detroit Muscle makes new ones)

I would highly suggest doing Nachos bulkhead parallel bypass. You run in addition to the OE 2 main in/out wires/4 brass terminals, with 2 new wires seperately around the bulkhead/thru a new hole/grommet in the firewall, like exits that curve around a border crossing/keeping the OE bulkhead 4 brass terminal connection OR just drill out the 2 bulkhead cavities for those 2 wires & run/solder 2 new wires straight thru with no brass terminals (leave 6" of the 2 wires behind the rear bulkhead half so if you have to pull em apart in the future you can do so).

Robert
Where does one find the info on "Nachos bulkhead parallel bypass",???.
Dave

http://www.madelectrical.com/electricaltech/amp-gauges.shtml

No. That's insane.

But I'm only half joking. They make people paranoid about the wrong things.

Nacho's parallel can be found by following the link I posted above. {to here: http://www.heritech.org/cuda/Charge2.html#Solutions, then here: Charging wiring upgrade at Dodgecharger forum
End result is something like RR described - a variation on the option Chrysler sometimes implemented.

End result looks something like this.

The decision of whether it will be helpful depends on the car and specific situation. If done well it doesn't hurt anything. But unfortunately I've been reading about too many 'bypasses' done wrong or badly and the result of each one is unfortunate.

Just last week a 'how to bypass' thread on IFSJA forum was revived by a well meaning person . It had pretty pictures, and put the entire electric load through the charging circuit - except for battery recharging.

:rant off:

Mainly the batt/alt/reg need to be in good shape/working correct & all terminals/connections cleaned/checked for minimal resistance (including ground paths) for a good charging voltage. & any load you can relay directly to the alt is to me a good plan: headlights/heater/AC/stereos.