Datsun Roadster Forum-311s.org

RustBucket wrote: ↑Tue Nov 27, 2018 1:44 am I'm not an electrical engineer so I stand to be corrected, but...

...and our roadsters ammeter design without the resistor (shunt) is the inherent flaw and the cause of the melting.
Rustbucket

In reality, the ammeters rarely fail - look at the size of the wire - its larger than everything else in the wiring harness. If something does fail it would typically be a solder joint. That is likely by design.

If the solder melted due to excess current - as pointed out earlier, it acted as a fusible link sacrificing itself to prevent complete meltdown (and fire) of the harness. Smart.

Unless you have a lathe and a way to replace the bezels, suggest you just replace it and be done with it. Plenty of used one's around - If you don't want original just get a Stewart Warner and you'll no longer have a concern.

I just checked the continuity across the coil on my "blown" gauge. The coil looks fine and I got a nice loud beep from the meter.
Once I got inside the gauge (no easy task as most of you know) I found that the black wire had literals blown off the attachment point.
the PO would not have been able to know that unless the gauge was disassembled.

Given I have continuity I would guess the gauge is functional.
What would be the best way to test it?

Wire it back in and see if you have power to the car.
Apart from the horn circuit, everything else goes via the ammeter.

Rodosuta wrote: ↑Sun Dec 09, 2018 9:09 pm What would be the best way to test it?

Hook it up in series with a headlamp or other load to a 12V battery. Should show discharge. If you wire it backwards it with show charging, but that still means it works.

Note the the ammeter circuit must be fully isolated from the case of the instrument. If either the black or white wire or coil touches the case, you will have a meltdown because the case is grounded by the dash- that is probably what happened.