Starter Solenoid Rebuilt But . . .

[Bingster]

Okay, so I've rebuilt the starter solenoid with a new relay on my 1947 De Soto. I'm bench testing the starter today, but the NOS relay has already been tested and it works. But a thought occurred to me before I bolt it onto the car.

 

I bought a 6v coil from Rock Auto and naturally it has the + and - terminals. Is the POSITIVE TERMINAL GROUND and NEGATIVE HOT as with the rest of the 6v system? Or is the POSITIVE TERMINAL HOT and NEGATIVE GROUND?

 

If it was designed for a six volt system it must be wired accordingly.  I looked at my wiring diagram for the car and it all checks out with the coil terminals unless the coil terminals are actually set up for 12v.

[Sniper]

If you're still the original 6 volt positive ground system then you want the positive of the coil wired to the points.

[DonaldSmith]

The points are what ground the coil, to make the spark. 

[Sam Buchanan]

The coil will function either way but the correct hookup is per the above posts.

[Los_Control]

Only times I have heard of problems is when you take a used coil and reverse the polarity .... IE, you take a old coil off the shelf that was used on a positive ground system, then use it on a negative ground system.

 

Seems the windings in the coil get use to running in one direction and at certain rpm's if polarity is reversed, you can get a strange miss that is hard to chase down.

 

At least that's my understanding .... does not mean it's 100% correct 

[desoto1939]

2 hours ago, Sniper said:

If you're still the original 6 volt positive ground system then you want the positive of the coil wired to the points.

So if you have the old style coil that mounts try the firewall with the armored cable from the ignition switch the negative connection is made at the bottom of the coil were it sticks through the firewall.  The positive connection which is the only visible connection point when the coil is installed properly then the wire runs to the connection point of the breaker plate.  Very simple concept.

 

So if you want to carry a spare 6 volt modern coil in your trunk as a backup to your regular coil that is a great idea. So you can get a modern 6 volt coil from NAPA very cheaply.

 

Now the question some one will ask how do you wire this unit up.  So the positive wire still runs to the breaker plate on the dizzy.  The armored cable from the ignition switch will need to be connected to the negative post on the top of the coil. So, you will have to make a long enough wire with ring connector attached on both end of the connector wire.  You will then need to have a bolt with lockwasher and nut so you can connect the end from the ignition cable to your jumper wire end.  You will then have to feed the other end of the wire out through the firewall and connect to the negative post on the new coil. or if you happen to have the coil spare mounting bracket in your spare parts box in the trunk you can remove the old original coil disconnect the negative wire remove the coil and the mounting bracket to the new coil, run the negative wire out through the hole in the firewall and connect to the negative post. Mount the coil to the firewall, connect the positive cable

 

below is a picture of the replacement autolite coil mounting bracket that would be needed if you have the type of coil that mounts through the firewall. found on ebay for $20.

 

Or find a temporary place to mount you temp coil and use plastic zip ties to hold inplace till you get home to make a permanent repair.

 

So if you are thinking ahead then you need the following items:

 

New 6v Coil.

Extra long wires to connect to the negative and positive connection points and ring terminal and nut with lock washer and nut, appropriate sized to your car/truck

Firewall or other coil mounting bracket

Couple of plastic zip ties  maybe 20 inches long with appropriate length to temporarily mount the spare coil

This all can be done for around $40-$60.

Might also need to make a new cable withe appropriate ends to run from the center of the new coil to the center of the dizzy cap.

 

Just a future safety tip.

 

Rich Hartung

Desoto1939@aol.com

 

Edited December 23, 2023 by desoto1939

[Sniper]

Without getting super technical As much as possible anyway Here's why wiring a coil up backwards is not a good thing period And while it might work in some applications and it won't work in others It doesn't matter Because it won't be working optimally regardless. And ignition coil is essentially two Loops of wire sharing a common ground. The loop that is connected to the points creates a primary magnetic field when the points are closed. This in turn also creates a secondary magnetic field in the part of the coil that is ultimately connected to the spark plug. When the points open the primary magnetic field collapses which also causes the secondary magnetic field to collapse. The energy in the secondary is what jumps the Gap in the spark plug. Only two things those two coils or Loops of wire physically share is the ground. When you wire the coil up incorrectly you are no longer sharing that ground and the magnetic field in the primary and secondary fight each other because the path to ground for the secondary is now through the primary Loop of wire. So the output of the secondary is reduced. Sometimes it is reduced to the point the car will not start or runs poorly so just do yourself a favor and hook it up properly and anybody that tells you oh it'll work backwards doesn't really know what they're telling you. If I ever get my engine oscilloscope project up and running I'll try to take pictures of the waveform wired both ways so we'll have a visual representation of the difference. Heck there might already be pictures on the internet of that already I don't know.