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A Few Electrical Questions - 1972 Plymouth

1918 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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Ammeter: IMO the issue is more the connectors and wire gauge than the ammeter itself. I reconditioned the wiring harness for my '74 Cuda a year or so ago. There were two connectors in that ammeter path that showed overheating issues - one is the connector from the engine at the firewall (8 pin I think not sure if this connector was used in '72) and the other was the bulkhead connector pin 16. The engine connector had already been bypassed by a previous owner and the bulkhead showed signs of heat - partially melted. The ammeter itself was fine. I replaced / restored the connectors and then put a HD bypass wire in parallel with the whole circuit . The issue is the original wiring is only #12 gauge - not enough for charging current IMO. The parallel ammeter bypass wire I put in is #7 gauge and I am not planning any upgrades on the alternator. Then the connector pins are also rated around 20 A maybe 25 I don't remember - but certainly not anywhere near 60A. If the battery gets depleted the charging current to the battery can be quite high. With age and with any heat those connector pins will oxidize increasing the connection resistance which leads to more heat which leads to more oxidation ... that's when it can get dangerous. I seem to recall I had issues with this on my '73 Satellite but that was a long time ago. MY bypass wire runs from the alternator output to the starter relay main terminal (that's where the ammeter cct terminates - be sure to include a suitable fusible link and I recommend dielectric grease on the connectors.
I don't know about a voltmeter conversion - my ammeter bypass may invalidate it altogether though I expect some current will still flow through the ammeter cct in parallel. I bought a digital voltmeter to insert in the cigarette lighter.

I experienced the rain issues in my Satellite - but not aware of a distributor fix for that - curious to see what others say.

Issue with amperage may come into play when battery gets depleted - though not sure how much current a depleted battery can absorb either. It may be limited by the battery's ability to take current. Either way I would definitely recommend an upgrade on the ammeter cct of some kind - even if you just put in a second parallel wire with separate connector pins that still runs through the ammeter - even if you stay at 60 A.

In the '74 manual that lamp on the switch panel is referred to as Ignition Switch Title Lamp. My Cuda has a light package so it also has a small lamp on the steering column to illuminate the key switch - not sure if both are part of the option package. These two are in parallel and are powered by a time delay off relay. Yes they come on for 15 secs or something when the driver's door is opened. I did discover today that I have an intermittent connection on the title lamp bulb as well - need to look into that - I just got the dash back in the car this week. I put an LED bulb in the steering column lamp - nice and bright. Could not find an LED for the switch panel title lamp as it mounts in a metal cylinder and shorted out any LEDs I tried.
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A shunt type meter set up as described in teh link for '75+ would require a different / recalibrated ammeter. As to resistance value the key is low - very low - and keep in mind that it will handle significant current so watch for heat - a potentiometer will likely smoke if you get it low enough to work.
Fusible link is there for catastrophic failure - if that link burns, replacing the link is the least of your worries,
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