The Stovebolt Site Forums The Shop Area The Electrical Bay 1955 1st Series conversion from 6v to 12v

I am restoring a 1955 1st Series Chevy truck and want to covert it from the 6v system to a 12v system and have question. I want to keep my truck looking original as much as possible and want to keep the push start peddle. I want to keep the 6v starter in for now as well. There is currently a Positive wire from the starter to the battery, a grounding strap from the starter to the frame, and a ground wire from the frame to the battery. Will this be a problem if i leave wired like this with a 12 volt system? I don’t want my system to catch fire. Here is picture of the starter

You can use the cables & starter that you have. They will work fine. You need to get a starter switch that goes on top of the starter for a 12 volt system. It has a term on the side that you hook to the coil to bypass the resister when the starter is engaged. You must put a resister in the circuit from the ign. switch to the + side of the coil when you change to 12 volts.

I would not be concerned with your ground straps or positive leads the way you described them, that is how most remain with 12V systems

someone converted my 53 GMC to 12 V
all they did was put a resistor in series with the original 6V ignition coil
changed the battery out for a 12V
burned out all the light bulbs

then they messed with the internals of the voltage regulator to make it charge the 12V system keeping the generator.
i have been concerned to open it up and see what they did in there
it is over charging the 12V a bit i find, but i haven't gotten around to messing with that yet

it's still running like that today, except i replaced the burned out 6V bulbs with 12V versions
my plan is to restore it back to 6V when i start poking at the electrical

My experience when I converted my 55.1 from 6 to 12 was that all I needed to change was the battery, coil, voltage regulator and bulbs. The 6v starter switch should be OK because switches care about amps not voltage and 6v systems have double the amperage as 12v. Some say you'll need to put a resister in line with the gas gauge but I didn't and had no issues. To be safe you probably should because mine might have been the "exception" to the rule. Your starter and horns will be fine as long as you don't abuse them.

Your also going have to swap the generator for a 12 volt model or better yet install a 12 volt alternator. There is lots of info in this forum for a 6 to 12 volt swap. Check of the Tech Tips by clicking on the link at the top of this page.

Quite right you are. A 12v battery doesn't do much good if it's still charging 6v.

By your first question, it sounds like electrical is not your strong suit. My advice is to be SURE you understand the conversion tip given in our tip section and the advice given by the fellows above, before you attach the final battery cable. It's not hard to understand, just need to be complete.

You need:
1. 12V battery
2. 12V externally resisted coil.
3. New starter mounted switch with side terminal
4. Ballast resistor.
5. 10si Alternator-best choice. Easy. Brackets. Gets rid of regulator and wiring, but not original.... or a 12V generator- original looking, expensive and may still use regulator.
6. Possible voltage reducers for gauges/heater fan motor.
7. 12V bulbs all around
8. $250

my GMC seems to work alright without step #3
however it did require a fresh 6V ignition coil recently as the original was starting to be so weak it couldn't start hot anymore, i probably would have got a few more miles out of it had i had that side terminal switch
but if the coil is going weak anyway i rather just change it a bit sooner than later
-s

Don't know what year truck you have. Don't know what all you have as far as ignition system. Sounds like you, or someone, did not convert to 12V properly.

The side terminal has nothing to do with saving a 12V coil in a 12V system. It is part of a bypass system that saves the points on a 12V, points motor with foot start.

what's a points motor?
i thought it was to put the full 12V to the coil during cranking
else you could use a 12V coil without a resistor?
the 6V coil is about 1.5 ohms so it would be a bit too hot with 12V without that resistor
-s

ah i think i know what you meant by "points motor"
yes
but that bypass side terminal if anything will hurt your points during cranking because it bypasses the resistor momentarily
if your truck starts through the resistor like it runs normally that would be the better alternative if it works
that side terminal was like belt and suspenders for a 12V conversion
-s

A motor that uses points ignition instead of HEI.

The side terminal supplies voltage to the coil during starting, as you said, so that when the starter tries to use all the power, the coil/points will get as much as possible. When you take your foot off the start button and starter stops drawing, that side terminal goes dead and the coil/points get their voltage thru the resistor. The resistor reduces the voltage to about 9V. The standard 12V conversion is done with a 12V externally resisted coil, a ballast resistor and a side terminal switch. A person can do whatever they wish otherwise.

right
there are a lot of pieces at play
12V coils with internal ballast resistor
12V coil without resistor
6V coil
old timey first generation 12V batteries that had so much internal impedance that the crank voltage dropped ridiculously

my truck is using a 6V coil, and the external resistor is meant to drop the voltage by half so from the ignitions point of view it is running on 6V still as original
there are a few ways to do it, what every shop or farmer did my truck was just the flavor of the week
-s

Your system is a doable alternative. However, while you are starting the truck on a cold day, or any day, you are getting a heavily reduced voltage to coil/points because the starter is drawing so much volts/amps. You are running the points thru the a resistor/voltage reducer while starting right when they need a snappy spark. If that does not cause any problems you are good to go and a lucky man, so far.
Whoever wired your truck was, as you say, a tractor man. Not done that way on trucks. You are messing with mother nature and father time will catch up to you.
There is only one right way. The other ways are wrong.

Bartamos, running new electrical in my truck isn’t my strong suit; however, I am having my brother who is knowledgeable help me. We had that one question as we were re-wiring the engine this weekend. I did replace the generator with an 10SI alternator, 12v coil, 12v bulbs all around, I have a voltage drop to attach to the fuel gauge so I can keep the original fuel gauge, and replaced all other accessories such as heater, horn, etc., to 12v.

Do I still need a ballast resistor? Also the wiring harness I have from painless wiring has the wires for the 12v coil, a MIDI fuse, the wire to attach to the starter and a wire for the starter solenoid. So i would attached the starter solenoid wire to the side terminal of the starter switch you mentioned, correct?

Pancho, Sorry I got off track talking to 2ManyTrucks.

I can not say what wire from the harness kit goes where without seeing the instructions and the kit, but here is how to wire. So just follow the harness wires you asked about and see if they will accomplish the list below. Not sure which wire they want protected by that fuse but you should be able to figure that out and install it.

Yes you need a ballast resistor.
1. Wire from the "ON" terminal on ignition switch to one side of ballast resistor.
2. Wire from other side of ballast to coil positive.
3. Wire from starter button switch side terminal to coil positive.
4. Big battery cable from battery positive post to large stud on starter button switch.
Start it up!

I assume you have a foot start starter not a solenoid. The coil should be an EXTERNALLY resisted 12V coil. Did you hook up the alternator correctly?
Still using the ammeter gauge? I don't like those.

Rule of battery connections when taking cables off battery posts. The negative cable is the first one off and the last one on.

Let me know if you need further.

Thank you Bartamos. Yes I do have a push peddle start inside the truck, which I would prefer to keep with the 12v system. Thank you for your advice

You can get the starter switch from Classic Parts. https://www.classicparts.com/1947-59-Starter-Switch-w_Side-Terminal/productinfo/53%2D712/