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A Few Electrical Questions - 1972 Plymouth

1923 Views 12 Replies 6 Participants Last post by  Grouch
As mentioned in another thread, I'm fixing up a '72 Plymouth Fury III. I have a few electrical items I'm curious about.

My biggest concern is the ammeter. I read online that with age, these can fail catastrophically (read as: car fire) since they carry the entire load of the alternator through the firewall into the dash. Mine is working at the moment, but I'm curious which wires under the hood run to the ammeter so I can bypass it if necessary. I also read that with ammeters in general (not with Chrysler ones specifically), they can be converted to work as voltmeters instead by adding resistors. Has anyone done this on their Chrysler vehicles? Sounds like a pretty straightforward conversion that could add some piece of mind to an old electrical system.

Next item would be the distributor. I remember growing up lots of people saying Chrysler vehicles ran poorly in the rain. My first car was a Plymouth, and sure enough, it did run poorly when it was raining. I later heard there was a very simple fix for this involving the distributor, but I can't seem to find that fix anywhere online. Does anyone know what I'm talking about? Seems like something I should do to this car while I'm fixing it up.

The old alternator in the car is weak (discharges when under too much load). I bought a remanufactured unit it and it solved my charging problem, but the bearings on the reman unit are already failing (surprise, surprise). I'm going to buy a new alternator instead and found an affordable, American-made one that puts out 95 amps. I assume the original was 60 amps. Any risk in going with the higher amperage? My understanding is it will only generate what the car "asks" for, so it doesn't matter. But then I thought back to the old ammeter; if it has an issue, it may "ask" for more current than what it actually should have. Wouldn't then a higher amp alternator be more likely to cause an electrical fire?

Last thing is very minor, but I noticed there are a couple little lights that shine on the ignition and headlight switch when getting in the car at night. Very cool idea, but they don't seem to work consistently. I'm curious how they work so that I can make them function properly. I'm speculating that they are supposed to come on when the door opens and then stay on for a minute or so after the door is shut.

Opinions or info on any/all of these four items are much appreciated.
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+1. The bulkhead connector was a weak spot. A high resistance and a high current equals heat. Look for discolored terminals and melted plastic.
If everything is clean & tight, you should be good. 50 year-old brass and copper connections are probably tarnished/corroded.
Automotive lighting Motor vehicle Font Rectangle Automotive design

Make sure that the nuts are clean & tight on the back of the cluster. The thick Rd & Bk wires are powered, disconnect the battery when servicing the cluster.
Product Rectangle Font Parallel Engineering

On the distributor, we drilled a small hole in the bottom of the housing to 'vent' the ionized gases or any moisture from inside. A vented distributor cap also works.
The weatherstrip between the cowl & hood is important to keep the distributor dry. Good plug wires with a 'smear' of silicone or dieelctric grease under the terminal boots will add an extra degree of weatherproofing. They also ease the removal of the terminals from the plugs or cap in the future.

Auto part Font Metal Gas Fashion accessory

There is a time delay relay for lighting important areas for a moment after the dome light goes out. It may be failing. It can come apart for inspection and contact cleaning, etc. if you want to try a Hail Mary on it first. It may be plugged into the fuse block or hanging around the steering column under the dash?
Product Rectangle Slope Font Parallel

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Turn signal switch wires wouldn't be snipped like that at the factory. Someone put in a different switch. LGn & Br would be for cornering lights that didn't go through the flasher (they stayed lit through the turn).

That snap ring does belong on the steering shaft. Spin the steering wheel nut on, grasp it with vise grips and pull the shaft toward you a bit. It will feel spring-loaded. You should see the groove that the ring slips into. After it is pushed down into the groove, it should stay put.
The scraping may be because of this.

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The ammeter only sees a small amount of the 60 amps in either direction (charge or discharge). It has a 'shunt' (parallel low Ω resistor) bypass that takes the brunt of the current. The shunt may resemble a bar of metal.

The shunt may be on the back of the instrument cluster's ammeter across the terminals (see my post #4). From there it goes to cavities #16 & #18 on the bulkhead connector.

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