wiring the ignition

[alanhaley]

I have been trying to figure out the wiring for my 51 one ton dodge. I have converted it to 12 volt and will install resisters for horn and dash instraments. I have started to build a harness like the one in the pilot house knowledge bank. The wiring diagram is excellent and easy to read except that I cant see how to wire it so that when the key gets turned left to accessory, the circuit for the coil is cut out. Isn't it important that this circuit not be energized when the truck is off and using accessories like the radio? According to the wiring diagram, no matter what position the key is in, the coil is energized. How can i be comfortable grooving with van morrison and making out with the wife or listening to the red sox knowing that the electrical system is not wired correctly? I took the problem to my auto parts store and they suggested installing a toggle switch dedicated to the coil, but this seems like the type of solution a ford owner might propose. Any ideas on the subject other then giving up necking with the wife and listening to baseball?

[Don Coatney]

Can you post a picture of the schematic you have?

[alanhaley]

You can see the diagram and photos of wiring harness at this url: http://dodgepilothouseclub.org/know/wiring_harness/wiring.htm

[Bob_Koch]

I don't think our truck had an accessories position on the key switch. So power to the coil is on when the truck is starting and also running. The other post on the key switch only applies power to the fuel gauge when the truck is running, but not starting. So, yes, power goes to accessories and the coil both. You would have to use a different key switch that has an accessories position, or use the toggle switch approach.

I don't know if the cars of our same era had an accessories position. If they do you might be able to use that and hopefully keep things looking original. If cars had the accessories position, then that tells you that Chrysler made them for things like making out (and ball games) , but not trucks.

[wallytoo]

if the trucks don't have an "accessory" position, why does the key switch allow the key to be turned to the left? in my '48, when i turn my key to the left, it allows the "run" circuits to operate, but i can't start the truck in this key position. the starter will turn, but it won't fire. as far as i know, the key switch is the original to the truck.

[Bob_Koch]

Then that should solve the problem.

if the trucks don't have an "accessory" position, why does the key switch allow the key to be turned to the left? in my '48, when i turn my key to the left, it allows the "run" circuits to operate, but i can't start the truck in this key position. the starter will turn, but it won't fire. as far as i know, the key switch is the original to the truck.

[grey beard]

Alan,

I made the schemtic you are using. Bob is correct - there was no accessory side to original Pilothouse ignition switches, so the issue was not addressed in the schematic. His advice is just fine if you wish to use a switch with this feature.

One oher thing you want to remember too - with your 12-volt conversion you will certainly need a ballast resistor between the ignition switch and the coil. AND, assuming you are making your new system negative ground like most 12-volt systems, you will need to turn the two primary coil wires around so the ignition polarity is correct. Lots of luck.

Any more questions, let us know.

[Merle Coggins]

I just looked at the back of my switch (because it's sitting here on my desk yet). It has 3 terminals. One marked AMP (ammeter), one marked COIL, and one marked ACC. I don't have a continuity meter handy to verify it, but I'm guessing the coil wire attaches to the COIL terminal and any other accessories would go to the ACC terminal. This would give you what you want (I think)

Merle

[wallytoo]

merle,

that looks like the switch in my truck. is it an aftermarket switch?

thanks,

wally

[Merle Coggins]

I have no idea. It's the switch that came with my truck. The key also works in the door lock, so I have to assume that it's the original key and switch.

Merle

[Reg Evans]

If a guy wanted to listen to his 602 or 610T back in the day while parked how would he do so without an ACC position?

[Don Coatney]

If a guy wanted to listen to his 602 or 610T back in the day while parked how would he do so without an ACC position?

That is easy. With the key off step on the brake and turn the turn signal switch on. This will back feed the ignition switch. Only problem is everytime the turn signal flashes you will lose the backfeed power so the radio sounds will be a bit broken.

If you dont believe me.....try it.

[Reg Evans]

I believe ya Don. I also heard that's why the dance "The Jerk" was invented.

[bach4660]

the instructions that came with the 602 shows it being wired back to the ignition switch and connected to the post marked "RAD" or RA on the schematic back in one of the earlier posts, or if you look at Merles photo, there is the coil or ignition, the gauges or amp and the Radio or ACC,

[alanhaley]

Alan,

I made the schemtic you are using. Bob is correct - there was no accessory side to original Pilothouse ignition switches, so the issue was not addressed in the schematic. His advice is just fine if you wish to use a switch with this feature.

One oher thing you want to remember too - with your 12-volt conversion you will certainly need a ballast resistor between the ignition switch and the coil. AND, assuming you are making your new system negative ground like most 12-volt systems, you will need to turn the two primary coil wires around so the ignition polarity is correct. Lots of luck.

Any more questions, let us know.

Thanks for the excellent diagram. I do not have a key for the ignition switch that came with it so I will have to use a modern one. I think I can figure out how to mimic the original switch except for the pole that goes to the gas gage. Someone mentioned that there was a specific reason for the lead to the gas to be through this pole, that the gage had to be disconnected when the ignition was on and the starter bumped; is this so?

Why the ballast resistor and what voltage drop should I use. If I use a 12 volt coil will i still need a resistor?

thanks for the help.

alan Haley

[wallytoo]

out of curiosity, i checked out the key-switch on my dad's '52 b-3-c. same switch, with the acc position. i'm confused now, as the odds of both trucks having the same switch, especially aftermarket, seem low. dad purchased his truck circa 1985, and i purchased mine in 2007.

also, as with merle's key, our ignition keys work in our passenger door lock cylinders.

[MBF]

If you use a 12V coil, you won't need the resistor, but will still need to reverse the + and - wiring on the coil. Mike

[Plymouthy Adams]

the 12 volt coil is VOLTAGE sensitive..the coil is designed to start on 12 volts yeilding a very high energy spark to fire off a cold engine..operated in small burst while spinng the starter..not substained use...once the key is returned to the run position..the voltage must travel through a resistor to prevent overheating the coil. (about 1.2 ohms)

Wiring the coil is straight forward for polarity now that you are going 12 volt negative fround. However it is the resistor inline that is of importance. The coil side of the resistor must have the 12 volt start voltage applied with ignition in start position, either by wire from the starter as the Sisson Choke operates or you can use a Ford style 4 post starter relay..where the fourth post makes contact when starter relay engages to transfer the 12 volt to the input voltage (now + terminal) of the coil. The 12 volt coil of external resistor is designed to run on the old 6 bolt battery standard where a good charging generator would apply 6.8 to 7.2 volts. That is why these coils are direct replacements for the standard 6 volt coils.

[MBF]

To clarify. The 12V coils that I purchased from my local NAPA are designed for direct 12 v input w/o a resistor. I installed these 6 yrs ago and have not had any type of problem with the coils (in 36 plymouth and 52 1ton) or the points in either vehicle. I did however install a ballast resistor on the heater motors as they remain 6 volt. The fuel guage in the 52 is not hooked up as the sending unit is bad, but the one in the 36 will have an inline (not ballast) resistor installed as soon as I find a working guage. I bypassed the ampmeter in both vehicles as they are a potential source for failure if accessories are added. I installed a voltmeter in both vehicles, fused the brake and marker light circuits as well as the heater motors and changed all the bulbs. I'm happy with the conversion to the internally regulated Delco alternators.

As far as the key switch goes, mine is the original 3 post. The accessory post is just a post to connect accessories to, but the switch is basically an on/off switch with only 2 positions-no accessory position. Mike

[Plymouthy Adams]

Yes as MBFowler states the internal resistor ignition coil can be used. It is designed for straight 12 volt application without need for the ballast resistor. However in this set up you do not gain the added advantage of "boosted" secondary voltage during the start cycle when rich fuel mixture and cold engine would greatly benefit.