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6v Positive Charging System Troubleshooting


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I own a 1952 Plymouth Cranbrook and I am having some trouble determining the best way to test the generating system.  Long story short, I had the generator rebuilt and a new generator regulator installed.  I drove it for a while and it seemed to work great.  One day after driving with the headlights on I had a loud backfire and the car was completely dead.  I had to get it towed home.  The following day the battery (without charging on my behalf) managed to revive itself for the engine to turn over and start.

 My thoughts are (a) the generator is not charging the battery or not charging it enough, causing (b) the ignition and accessories to run off the battery, which (c) drained the battery, causing (d) the fuel to not fully ignite and then backfire on the next stroke.  I tested the battery and it came up as -6.25 volts (which I assume is negative because the car is positive ground) so I assume the battery is ok.  What is the best way to test the generator?  Should I polarize the generator, with the idea the mechanic may not have known to do that?  My understanding is my car has a Type B generator regulator requiring me to touch the BAT cable to the Field Terminal (NOT the armature terminal) at the generator regulator, correct?  Here is a photo of the setup I have now and some car photos.

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52 Plymouth 1.jpg

52 Plymouth 6.jpg

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52 Plymouth 9.jpg

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You need to measure the voltage at the battery with the engine running.  Also, observe the ammeter needle when you first start it, it should swing towards the + side.

 

I also suggest getting a service manual, it won't have everything but with that and the folks here you should be covered.

 

https://www.rockauto.com/en/catalog/plymouth,1952,cranbrook,3.6l+218cid+l6,1349872,literature,repair+manual,10335

 

 

Edited by Sniper
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It doesn't matter if your car is a positive ground, if you put the red (+) lead of your meter to the (+) terminal of the battery and the (-) lead of your

meter to the (-) terminal of the battery, you should read +6.25 volts.   6.25 volts is a reading of a good battery.  Leave your test leads connected, 

start the engine and move the carb linkage to off-idle at about 1500 RPM and your meter should read about 7.10 volts +/- if your generator is 

charging the battery and the voltage regulator is set up correctly.  The amp meter in the dash should be on the + side of zero at this higher RPM.

 

Also, from looking at your photo of the engine bay, the heater duct from the back of the heater to the firewall is available.  Someone who advertises

in The Plymouth Bulletin is reproducing them for your car.

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Thank you for the replies!  I do have a service manual but my experience is with modern Japanese cars so it can be confusing sometimes.  As long as the generator is showing an output at the battery of roughly 7.10 volts at 1500 RPM then I can assume the generator is polarized, correct?

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Once you get the charging system sorted out on your very nice car put a set of 6v battery and starter cables on the to-do list. The 12v cables in your car are not letting the battery push all the amps to the starter. Here is what 6v cables look like (my car is negative ground):

 

battery-cables.jpg.a6d038db0ab055e49f8936293293988a.jpg

Edited by Sam Buchanan
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Just curious about your new replaced regulator. Where was it built? I heard the the new reproduction, made overseas regulators have about a 50% chance of actually working when newly installed. 
 

How’s your tools and mechanical experience? Willing to give it a shot? Polarizing the generator won’t hurt anything if you go ahead and do it again. A digital multimeter on the battery while revving up the running engine should provide some clues. 
 

I don’t own one yet, but plan to get one: a clamp style ammeter. For DC voltage. With a fairly high maximum read value. You clamp it around battery cables and it reads DC amps flowing through. It’d be great to see how many amps a generator is putting out. Also how many amps a starter may be drawing. You can clamp it on the starter cable. Leave it and go start the car. Come back and look at it under the hood. It records and holds the highest amp reading recorded on the screen. 
 

Could likely also use it to find bad grounds. Pulling amps from the battery when the car is parked. Running too. See too many amps are going thru a circuit. Indicating electrons going to ground when they are not supposed to. 

AC amp selection on the tool will test alternators too. 
 

I gotta get on this and order one now. I just talked myself into one. 

Edited by keithb7
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52 minutes ago, ChrisMinelli said:

You know, I didn't even know / notice my wires are too small for the 6v system.  Do you think that could have some effect on why the battery drained on that particular instance?


Probably not, I suspect your gen/regulator is the culprit in not charging your battery. I tried a new Advance Auto regulator and it was dead on arrival. I fixed my charging problems with an alternator.  :)

 

The mongo cables are needed for reliable starting, the 6v starter pulls huge amps.

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The generator is original — I had it rebuilt at an electrical shop in Chicago.  I’m going to run it through some tests today with the multimeter after reading a I’ll service manual I borrowed. 
 

Just so I am sure, and because the service manual does not specify: for my type of regulator i flash the Field with the Battery wire to polarize, correct?

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Why do you think that your trouble is in the charging system?  You said that the engine backfired and stopped.  Perhaps you should check the ignition points gap and perhaps the timing.  Another thing to check is the carb float, it may have stuck and caused the engine to flood.  Check the battery voltage at 1500 rpm as suggested. If it is OK then look at these other possible problems.

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Check the bundle of wires that are connected to the battery side terminal of the starter solenoid.  This is the main feed for all electrical circuits in the car.  Loosness or corrosion here will effect everything.  Clean each wire connected here and retighten everything.  If you car doesn't have a ground strap from the firewall to frame or engine install one.  Your shop manual should outline a simple test to determine whether your Genny and vr are working correctly.

Also assure the lead from the ignition switch is on the negative terminal of the coil.

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4 hours ago, busycoupe said:

Why do you think that your trouble is in the charging system?  You said that the engine backfired and stopped.  Perhaps you should check the ignition points gap and perhaps the timing.  Another thing to check is the carb float, it may have stuck and caused the engine to flood.  Check the battery voltage at 1500 rpm as suggested. If it is OK then look at these other possible problems.

The reason I think the charging system is to blame is the car was completely dead when I pulled over.   It wouldn’t turn over at all.  I suspect that the battery would not be dead if the issue was the ignition or carb. 

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If the battery had gone dead to where the engine died and would not restart, it’s unlikely that it would recover enough, from resting, that is would be able to start the engine again. It’s more likely that you have a bad connection issue somewhere that disconnected when things got warm. Then made new contact upon cooling down. 

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23 hours ago, Merle Coggins said:

If the battery had gone dead to where the engine died and would not restart, it’s unlikely that it would recover enough, from resting, that is would be able to start the engine again. It’s more likely that you have a bad connection issue somewhere that disconnected when things got warm. Then made new contact upon cooling down. 

 

Ignition switch??

 

Kinda related.....the switch on my car doesn't "turn on" until very near the end of the key's travel. I was concerned about the switch failing at an inopportune moment so I installed a toggle switch up under the dash that "jumps" the keyed switch. If the ignition switch fails,  the toggle switch can hotwire the ignition to get me home.

Edited by Sam Buchanan
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Quickest way to to if the generator is working is to start the car then remove a bat cable if it stops your generator isn't working .I will stand corrected if that isn't true .I had this same problem with my rebuilt generator ,did what you did drove it like that the whole summer just kept charging the battery .Eventually cleaned all contacts tore the generator apart again found oil cleaned it all repolerized the gen.and away it went.

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   Cleaning the connections at the amp gauge solved my stalling problem. Disconnect battery ground, have your light, nut driver, emery cloth, dielectric grease and whatever else you might need at hand. I only wanted to crawl into that position once. 

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I had to put a new IGN switch in my Studebaker, it would start, run fine the just shut off, would restart no problem, run fine then shut off. A friend just had the same happening to a 49 Ford he just purchased.  New switches, problems gone.  Make a jumper wire with two aligator clips on both ends. Power the coil from the battery and see if the problem resolves. If you can drive it around with the jumper in place, it pretty much confirms a failed switch.

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  • 3 weeks later...

This is still driving me nuts, but I think I may have found the issue -- am I correct in saying a continuity test between the field terminal of the generator and the armature connection at the generator regulator should NOT be continuous?  (And vice versa between the armature terminal of the generator and the field connection at the generator regulator?)  I think the wires are touching each other somewhere along the line.  How do I determine which post on the generator is which without dismantling it? 

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If your wires are still attached to the regulator, I would recommend you do a continuity test with multimeter to determine which is which. Someone may have switched them around in the past.

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