54 Desoto Alternator Conversion

[JasonG]

I decided to replace my generator on my 54 desoto firedome with a 1 wire 6v positive ground alternator. I got the alternator bolted up,but I'm a little confused on the wiring. I ran the wire from the alternator to the batt terminal on the voltage regulator and disconnected the arm & field wires. I had 2 wires under my arm terminal on the voltage regulator and one under the field. After disconnecting them I now have a no crank, no start. One of the two wires under the arm must be providing power to the ignition. My wiring harness is all taped up and I ran out of daylight yesterday, so I'll have to try to sort it out later today. Any idea why there is 2 wires under the arm and how should I go about configuring this now? I attached photos of the regulator before the conversion.

Edited February 3, 2022 by JasonG (see edit history)

[JimKB1MCV]

Yep, things like that happen in the most surprising places,

Maybe its because most of the machinery we're dealing with is well past its projected lifespan.

 

I spent several years of my working career keeping a 1934-built tanker (ship) afloat and operating and making enough money to make payroll. Mostly successful. 😊

 

Are you sure the alternator is the way to go on your car? Those Mopar electrical systems are pretty robust abd just about bulletproof.

 

Good luck.

 

 

 

[61polara]

Always check the factory wiring diagram before making modifications to see what you are impacting.  The 1954 DeSoto starter relay is grounded through the regulator to the generator to prevent engaging the starter while the engine is running.  With no voltage output from the generator, the relay ground flows through the generator.  When the engine starts and the generator begins to put out current the ground for the starter relay is lost and the starter will not engage.  Looks like you've lost your ground for the relay.

Edited February 3, 2022 by 61polara (see edit history)

[61polara]

Do you still have the factory starter relay or has it been changed to a Ford style (or another style) relay?  It's located on the inner fender beside the battery.  Post a picture of your relay and we'll see if we can help you.  I've just mostly figured out what a prior owner did in converting the starter relay on my '54 DeSoto Firedome to a Ford style relay.  At least I have the starter engaging by turning the key now and the engine starting.  Also, the neutral safety switch is wired through the starter relay, so you may have an issue there now as well.

[JasonG]

It's the original relay mounted on the fender. I attached a picture of it. The 2 green wires were for an aftermarket push start that the previous owner put in which i have since removed.  If i lost my ground for the relay, would that second wire that was under the arm be a live wire?

[TerryB]

Wouldn’t you connect the alternator output to the armature terminal on the regulator?  That is the same terminal the output voltage from the generator would have been connected.  The field from the regulator no longer is needed since the alternator has its own internal output regulation.  The regulator’s internal cut out should still function to disconnect the alternator from the battery when the engine is not running..

Edited February 3, 2022 by TerryB (see edit history)

[Bloo]

No, you wouldn't unless you were trying to still regulate with the old regulator. Then you might. Trying to use the old regulator is rarely done, so that probably isn't the case. Typically the regulator that was intended to be used with the alternator is used. Sometimes that regulator is internal to the alternator, sometimes it's external.

 

The effective "output terminal" on a generator system is the "BAT" terminal on the regulator. The large power lug on the back of an alternator is the equivalent "output terminal". It's true whether the alternator is internally regulated or externally regulated.

 

Unlike a generator system, an alternator does not need a cutout or a current regulator, only a voltage regulator. The charging current does not need to flow through the "regulator box" like it would with a generator. That's true even when the alternator's voltage regulator is external.

 

I think @61polara is on to the problem here and the start relay is probably not grounded.

 

Edited February 3, 2022 by Bloo (see edit history)

[TerryB]

Yes Bloo, looking at the regulator from a strictly goes in - goes out it would seem the armature input voltage point does indeed then get connected to the battery internally when the internal cut out of the regulator makes connection. Bypassing the cut out function by connecting the alternator to the battery terminal directly means you could replace the regulator with just a terminal block.  I never was involved in making this change on anything I own so it’s new turf for me.  
 

This is the regulator circuit I was looking at

 

[61polara]

From your picture, it looks like the brown cloth wire is connected from the small terminal on the right to the terminal on the left.  If so, someone has already bypassed something. 

Edited February 4, 2022 by 61polara (see edit history)

[Ben Bruce aka First Born]

I agree with Bloo and Polara.  I am nor familiar with the "starting " circuit on a DeSoto. On  the Buick, with the pedal start, the solenoid was grounded through the generator. Grounded when NOT charging.  A soon as the generator began charging, the ground was broken and starter could not be engaged.  I simply grounded the wire that was connected to the generator.  The Arm wire to the regulator I attached to the Bat connection at the regulator. I BYPASSED THE AMP METER.  For charging, the alternator wire can be run directly to the battery. 

 

  Ben

[61polara]

9 hours ago, JasonG said:

It's the original relay mounted on the fender. I attached a picture of it. The 2 green wires were for an aftermarket push start that the previous owner put in which i have since removed.  If i lost my ground for the relay, would that second wire that was under the arm be a live wire?

Looking closer at your starter relay, it appears to be wired correctly.  The green wires that the prior owner wired to a push button starter switch bypass this relay by applying power from the main power terminal directly to the solenoid. The two brown wires are two different wires coming out of the harness, which I didn't see before.  The one connected to the terminal on the left is the power input from the starter key switch and should be hot only when the key is held in the start position.  The brown wire attached to the ARM terminal on the right goes to the ARM terminal on the voltage regulator.  This is the ground for the relay solenoid coil in the relay not the one on the starter.  When the key is turned to the start position, voltage flows to the IGN terminal on the relay which applies power to the solenoid coil in the relay.  This coil is grounded through the ARM terminal to the voltage regulator and then the generator as a safety feature to prevent the starter from engaging while the engine is running.  You can jumper the IGN terminal to the SOL terminal (or move the wire to the IGN terminal from that terminal to the SOL terminal and bypass the relay internal solenoid.  This is the same as the PO has done with his push button starter switch.  Or you could ground the ARM wire.

 

These relays are very hard to find and very expensive when you find them.  If yours doesn't work, try opening the case and clean the contacts inside and you may save it.  Hope this will get you going again.

[TerryB]

I’m assuming this is the V8, does it have a Power-flite auto trans?  I have the 1953 DeSoto shop manual and I’m looking at the wiring diagram.  In one version of V8 schematic, the second wire on the armature contact of the voltage regulator goes to the transmission neutral safety switch.  The neutral safety switch then connects to what looks like the “ARM” contact on the starter relay.  The second V8 schematic in the book shows the second wire from the regulator armature tab goes directly to the starter relay, no neutral safety switch in the circuit.  The connection on the starter relay is not identified with any markings.

 

Again, this is a 1953 DeSoto shop manual.  Maybe this is of some help.

[61polara]

TerryB you are correct, I just simplified it a little not going into the neutral start switch.  The bypass I suggested will bypass the neutral safety switch as well, so the starter will engage in any gear and will engage with the engine running.  These are about the only options if Jason wants to keep his one wire alternator.  Going back with the original generator will restore these functions.

[TerryB]

Good info Dave!  You are hands on familiar with this setup, I’m just looking at a book to see if II can add anything useful.  

[JasonG]

Thank you everybody for your help and expertise. I grounded the wire for the relay solenoid coil and the car started right up. The alternator is charging correctly and the ammeter is working as well.

[TerryB]

Great! Glad to hear that.

[61polara]

Glad we could help you.  Still working on the challenges of my '54.  Stay with us here and I hope you have joined AACA and a local region.