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hduff 07-06-2013 03:36 PM

54 Desoto Firedome Wiring Confusion
While working under this car, I noticed this:

The device with two terminals on the side of the transmission may be a neutral safety switch, or it may not. I know that switch is located there in the 727 trans, not certain about this one. I don't see a neutral safety switch on the wiring diagram.

To make matters worse, I have four wires with male connectors that would connect to this whatever-it-is switch (if they need to be connected at all), none of which were connected and are so old, I cannot read a color code from them. For the life of me, I cannot find two more unconnected female connectors anywhere (the brake switch and wires are accounted for). No equipment appears to be missing from the area that the wires would connect to. I'm not aware that these wires were connected to anything when the engine would start and run (not doing that now), but they could have been and are the cause of my starter problems.

I only have the '53 schematic to work from and AFAIK, there is not an overdrive unit on this car.

Can anybody with knowledge of 50s Mopars identify this stuff before I have to spend hours tracing 60-yo wires to try and figure it out what it is and does?

LATECH 07-06-2013 04:41 PM

Test the switch. Plain and simple. Put an ohmeter across the terminals.
See what it does. If it conducts while the trans is in reverse, then it is a reverse light switch.
If it conducts only in park or nuetral, then its a nuetral safety.
That will help you narrow down the wire question as well.
Hook an ohmeter to the solenoid energize wire on the starter , and probe the wires at the switch in question. If you have continuity on one wire, then you have the wire from a nuetral switch.The other wire will be from the key while in the cranking position. Simple logic...just think about it for a few minutes, and use an ohmeter.:thumbup:

hduff 07-06-2013 04:48 PM

Yes! That does make sense.

Joe G 07-08-2013 05:02 PM

2 Attachment(s)
Hey, Duff, I found my '54 book. Attached are a wiring diagram for a '54 Firedome, and an exploded view of a Powerflite transmission.

Looks like there should be two switches on the transmission; a neutral safety switch, and a back-up light switch. I believe the switch you have pictured is the back-up light switch. Judging from the drawing, the neutral safety switch should be just around the corner on the back of the main transmission case.

I would bet that the two smaller wires go to the back-up light switch and the two larger wires go to the neutral safety switch.....but I am only guessing, Some simple tests as Latech suggested should help you get it sorted out.

Hope this helps...:thumbup:

hduff 07-08-2013 08:00 PM

I can't believe I missed that other switch!

Thanks for the '54 schematics.

After some testing, I have the wires correctly connected.

Yet now I still get just a single click when I try the starter, so I'll check the continuity of the N/S switch and then pull the starter itself to check it if the switch is OK. I'll need to pick up a 5/8" obstruction wrench from Sears on the way in tomorrow in case I need to remove the starter. I've never needed one of those until now.

hduff 07-10-2013 04:52 PM

I checked the neutral safety switch and it works correctly. I'm glad because I would not look forward to sourcing and replacing that.

After a trip to Sears to purchase a 5/8" obstruction wrench (I've never had need of one before, but there's no way the top fastener can be removed without one), I was able to remove the starter and test it. (The image is rotated 90 degrees counter-clockwise.)

The solenoid will engage as it is supposed to do, but the armature will not spin. That piece of tape sticking out was wrapped around a brush lead to keep it from shorting out on the case. As far as I can tell, while the tape was loose, it was not shorting out.

So I'm soaking all the threads in Kroil (I love that stuff) and looking for a re-build kit.

hduff 07-13-2013 09:35 PM

I got a 24-hour turn-around from a local shop on the re-build, so I took that option. Turns out there was an intermittant short and the brushes were shot.

Bench tested it and it works fine.

LATECH 07-14-2013 07:08 AM

Good deal. :thumbup:

hduff 07-14-2013 10:18 AM


Originally Posted by LATECH (Post 1694095)
Good deal. :thumbup:

The kit was around $40 plus shipping and a few days delay for delivery; re-build was $110. The local shop, Browning's Alternator & Starter Exchange has been in business for decades and enjoys an excellent repuitation. A no-brainer for me.

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