Black and red 12G wires on instrument cluster

[Vanderstel]

1967 Satellite, I just installed a new under-dash harness from Year One. Fits very well. One question...

There are two, I think 12G, wires coming in, red and black coming to the back of the instrument panel, they attach with nuts.

One the instrument panel the red is labeled as POS or +12V, but the black in NOT labeled as GRD.

Is the Black also +12V and where does it go? My wiring diagram shows it going to the alternator?

 

[Don67Satellite]

You have a FSM? Those wires go to the ammeter on the rear of the dash & out through bulkhead. Yes, BATT and ALT.

 

[davek]

gos to this

 

[1 Wild R/T]

The choice to make that wire black wasn't the best... It needed to be identifiable from the other (red) wire but it's 100% not a ground even though black is typically the color used for grounds in the automotive world...

 

[Nacho-RT74]

as mentioned, both are actually toward to handle positive, ALTHOUGHT black wire will be hot just once is conected to the ammeter along with the red wire AND also with engine running since comes from the alt output.

they can be connected on either side of the ammeter and will work the same just with a reversed reading. Hence why the cluster is labeled RED on one of the amm studs provision, to assure the reading will be the correct one.

once both wires are connected the gauge will sense where comes or goes the current To feed the car needs. If the batt is feeding totally or partially the car load demands, will show discharge because it means the battery is being discharged.

if it shows charge, it means the battery was previouslly discharged and the alt is charging at the same time is feeding the car load demands.

if reads death centered and engine is running it means the battery is fully charged and the alternator is able to hold and feed all the car load demands. This is the ideal status of the charging system.

 

[Vanderstel]

Is the amp meter really a serious failure point? I read a lot about how they are weak link and should be bypassed, maybe replace by simple volt meter? Although isn't an amp meter giving a more accurate information about what the charging system is doing?

 

[72RoadrunnerGTX]

Any neglected, abused, or poorly maintained electrical connections designed to handle any kind of current can be prone to failure. Do some searching here under “ammeter” or “voltmeter conversion”, plenty of fact-based counterpoints posted to the “spontaneously combusting” ammeter myth.
Weak link? The real weak link in the original charging system is, always was, the charging system Packard terminals in the bulkhead connector, by-pass those, secure the ammeter connections correctly. Don’t incorrectly connect any add-on loads on the battery side of the ammeter.

 

[Vanderstel]

My electrical shop just confirmed my ammeter is bad, blowing the fusible link. I have new engine and under-dash harness which includes new bulkhead connectors.

Given everything I mentioned, right now I'm leaning towards simply replacing the ammeter with a new one.

 

[72RoadrunnerGTX]

Blowing fusible links? That would indicate an ammeter terminal insulator failure, nothing internal to ammeter can short like described. Insulator failures are normally caused initially by over-tightening the terminal nuts, crushing the fiber insulators. Or being left loose enough to allow resistance/heat to build up over time.

 

[Nacho-RT74]

Would you replace the wheel due a flat tire or just replace the tire?

check it first. Could be just the insulation.

 

[kiwigtx]

Insulator failures are normally caused initially by over-tightening the terminal nuts, crushing the fiber insulators.

^^^^^Exactly this ....a careless worker at your Electrical shop thought he was torquing up the crankshaft dampener.

 

[Nacho-RT74]

Take in mind there are two insulators, one on each side of the housing, inside and outside

 

[Nacho-RT74]

One note more. The ammeter studs nuts must be just tight enough to hold the gauge. Then the second nut to hold the wire must be more tightened, but BETWEEN nuts, so the bottom nut must be hold while tightening the second nut to the wire.

 

[72RoadrunnerGTX]

Same can be said when disconnecting the ammeter leads, if this connection is not treated a double nut, lower nut not held secure while tightening or loosening the upper, there is a high risk of twisting the stud and damaging the internal stud head to bus connection. Leading to high resistance and/or insulator failure, then it would be attributed to that “dangerous” old Mopar ammeter. In this scenario, the failure would actually fall under the classification of abuse. In some cases, the damage may not be visible externally.

 

[Vanderstel]

I'm not really good with electrical so I'm learning as I go. After installing the harnesses I blew the link and so... I became very nervous about proceeding, I didn't want to screw anything up. I reached out to the local Mopar club, but no dice. I don't have any friends that know this stuff. The electrical shop found that bypassing the ammeter no shorts occurred.

Current status: The heavy gauge black & red wires are joined to bypass the ammeter and everything seems to be fine. I drove it home yesterday from the shop, wipers, headlights, brake lights, turn signals (inside & outside), interior lights, temp gauge, fuel gauge all work.

This is what I know.

I have not yet pulled... for the billionth time, the instrument cluster and inspected anything. I don't how to determine a good ammeter vs a bad one, or what insulators I'd be looking for.

So for now, I'm want to sneak up on a solution, one thing at a time. From the image above (72RoadrunnerGTX) of the damaged ammeter I can assume mine is damaged in some way. So back to my earlier plan and that is to replace the ammeter, put my red and black wires back and I should be good.

 

[copper67sat]

Here is what the 67 Plymouth B-body ammeter should look like.

The ammeter and oil pressure bezel is held to the cluster by the ammeter nuts on the back and a screw by the oil pressure on the front. There is a nylon washer under the screw. Remove the cluster bezel to access the front.

Remove the ammeter and you can see the insulator. That part is likely damaged or missing on yours causing the ammeter to short to the housing and blow your fusible link.

 

[Vanderstel]

Thank you, I'll take a look

 

[1 Wild R/T]

Another thing to be aware of is the studs need to be centered in the square holes in the gauge housing... One car I got involved with fixing I sold the guy a replacement fuel gauge & a few days later he was back wanting me to give him his money back... I knew the gauge was good so instead of just giving him his money back I offered to take a look at it... When he assembled the cluster he'd shifted the fuel & temp gauges grounding out the studs... It took out the IVR... If he'd grounded out the Ammeter he would have blown the fusible link like you experienced...

 

[72RoadrunnerGTX]

Yes, there are some slight ammeter mounting variations from one year to another and from one cluster design to another. Should be noted that the inner insulators are also keyed by the slot at the ends to keep the studs centered in the holes through the cluster frame. If the inner insulator become damaged, as pictured, the slot on one end is gone, it can allow the ammeter to shift and the studs to contact the cluster frame.

Interesting, the ammeter pictures posted by copper67sat showing the ’67 damaged insulator does not appear to show signs of heat or arcing to the cluster frame, that would indicate the insulator damage was likely caused by over-tightening of the stud nuts.

 

[copper67sat]

Interesting, the ammeter pictures posted by copper67sat showing the ’67 damaged insulator does not appear to show signs of heat or arcing to the cluster frame, that would indicate the insulator damage was likely caused by over-tightening of the stud nuts.

The pictures are of a spare cluster that came out of a car I drove for several years and then parted out almost 30 yrs ago. Never had electrical problems with it even though the insulator is missing a corner. I doubt it had ever been apart before - certainly not by me, but I didn't see the missing piece in the housing. The ammeter actually mounts to the circuit board and not the housing itself. Nuts on the back were snug, but not tight - I removed them with my fingers.

When I restored my Satellite in the early '90's, the insulator disintegrated when I disassembled the cluster so I scavenged one from another spare. More evidence that this is a delicate part that's easily damaged if the cluster has been disassembled. I didn't remember the nylon washer/bushing from before, but it's likely also important for isolating the gauge from the housing.

If you look closely, the back of the circuit board is stamped RED above the left ammeter stud and BLACK above the right one so you know which way to wire it.