VCCA Home Forums TECHNICAL - GENERAL Electrical - 12 volt 12 volt conversion gone haywire

Well, we took Maddi (our 1950 Chevy, Styleline) out for here maiden voyage. Went about 10 miles. Found the few things I need to do before I can get out on the road with her. Before I got her, someone did a 12 volt conversion. I have no idea if they had a clue what they were doing. I have headlamps and tail lamps. I do not know if they put in a voltage reducer or just changed out to 12 volt bulbs. No directional lights (it has the add on switch), no gas gauge, no dash lights and no horn. A bunch of the wires under the dash have been cut (ie: cigar lighter and radio) I can see where a new heater/defogger fan was installed (yep, another add on), again I do not know if it was upgraded to 12 volts. OK guys... Any advice is more then welcome, like where to start and what to look for. It has been only about 45 years since I worked on one of these. Thanks in advance.

My advice is to change it back to 6 volts. You can then re-connect your wires and fix your problems without worrying about burning things up. A properly functioning 6 volt system will give satisfactory service.

Mike

I saggiest that your best approach is to start with a wiring diagram for the car. The circuits are the same regardless of the voltage.

It will take some time and patience to trace each circuit. That will help you identify which wires are properly connected and where there are problems. Along the way you will be able to confirm the condition of the wiring. Closely inspect the insulation for cracks and confirm that the terminals are still securely attached to the wire. I would even consider taking each connection apart and use a small brass wire brush to polish the contacts.

You are working with a 70 year old vehicle. Insulation gets hard and breaks and connections oxidize. Everything needs to be properly grounded to the chassis.

Start with the simpler circuits such as the taillights and brake lights. That will help you understand how to read the wiring diagram and track the circuits. That will give you the confidence to handle the more complex areas such as behind the dashboard. Invest in a decent volt-ohm meter if you do not already have one.

Whether you stay at 12 volts or go back to 6 is a secondary decision. I expect that you will learn things while you trace the circuits to help you make that decision.

Checked fan and lights and they are all 12 volt as well as the alternator. Think I will stay with the 12 volt system. I know some of the wires have the insulation broken off and I think I will address this (as Rusty suggested) when I go with one circuit at a time. Going to check forum and find a wiring diagram and start "plugging along".

If you go back to 6v check the gauge of any wires the prior owner replaced. Someone else here can better explain this but I was told when starting the job of rewiring my 6v 41 that a smaller gauge can be used with a 12v system than a 6v will safely support.

I'm keeping there 12 volt as they did do a lot of it right. I wish it was 6 volt. then I would have put a 12 volt motor cycle battery in her to "run" a few of 12 volt things for the wife. But, I'm kind of stuck with the 12 volt system. Traced wires, lots of wires, and got most of the stuff working again. Most of the problems I ran into so far are insulation falling of the old wiring and grounding out. Fixing some and replacing others. Dash lights and gas gauge next for wiring. But for now taking a brake from wires and doing a few other things.

The old rods in the gas throttle linkage are worn and very, very sloppy. I will be taking out the old rod system and replacing with a cable throttle. That way I can drive Maddi (1950s Styleline's name) until I can put the rods on the bench to repair, replace and fabricate parts and get it all working again. Then I will probably reinstall it. I will only have an extra hole to plug that way and still enjoy the ride while working on that.

In about a month I will be putting her in storage for the summer and heading back to the "North-land". When home I can scavenge parts from my "rust bucket" Chevy to use on this one. I have many memories coming back while I am working on her. The wife just wants to ride and I enjoy the fix. I will just keep plugging away. Oh yeah, Thanks guys!

Hi Jeff,

That sounds like great progress. You just have to be organized as you work through the harness.

Given the condition of the wiring that you describe I suggest you might want to consider a replacement wiring harness as next year’s project. Good harnesses are not cheap but the alternative is very expensive. A wire shorting to ground can cause a fire.

When I got my car I immediately recognized that I would never be able to safely connect a battery. At least half the wires that I touched had insulation falling off. There were a lot of bare wires visible. I paid the money for a good YNZ reproduction harness and installed it. I have not had any wiring issues in the 5 years I have been driving the car.

I assume that you will disconnect the battery before you head north for the summer.

I also used a YnZ harness in my 48. Installed in 2012. I removed the seats so I could throw some blankets on the floor and lie down on them to do everything under the dash. The 6 volt wiring will work great on your 12 volt system. Here is a site that has nice colored and laminated wiring diagrams. https://www.classiccarwiring.com/

Well, today I was checking things out and all of the sudden she quit. Went to checking wires. Then the blue/black smoke started to roll. It seems the switch shorted out and a few of the wires burnt. Rusty is right. Next years project will be installing a new wiring harness. Going to just get her running to get to storage this year. Now the search is on for a good, but decent priced, harness for my '50 stlyeline.

One good thing I noticed is that when "whoever" converted to 12 volts he unhooked all the gauges. Now when putting in a new harness, I just need to put gauge voltage reducers when i hook them back up. Any ideas on a good & cheap wiring harness will be appreciated.

Checking prices and I think I will go with making my own harness Not many circuits or wires. I will just pull wires and put them in a standard fuse box.

UPDATE: I had a helper with me today. My grandson, who is 11 years old, wanted to help. What a help he was! We went through and found any bare wires and he went and taped over them (some with liquid electric tape) to keep anymore short circuits at bay. Looked over his work and he did a very good job. Only missed one and had the rest covered well. We then went through the engine wires. Another mess. I found out why points were getting burnt, a hot was connected to the points all the time. Again my Grandson used the testers and found out where things were messed up. He liked learning about the car. We then pulled a few new wires and got her running. I have a "makeshift" key. The light switch on the floor deal. Ordered a new key switch. We had to remove it from the bottom as the spring catch would not compress. After I ordered the whole new switch (switch & tumblers), the two of us went to the garage and with some patience and a lot of PB Blaster, we got the tumblers out. Still debating on if I should make my own wiring harness or order one. This HAS TO be done. I did find a few on EBay (EZ wire) that were not to bad of a price. Comments and advice are more than welcome. PS: The wife is starting to get mad about me working on the car too much.

Well done teaching your grandson. I f your wife continues to complain start getting under her feet then she will send you to work on the car.
Tony

Hi Jeff,

I strongly encourage you to look beyond price when you select a wiring harness. I have used an EZ wire in a '49 Chevy pickup. We got everything to work but it took some study and patience. It was not just a "plug & play" activity. There were wires we had to put terminals on and some we had to splice after cutting different wires to length. Plus wires that we did not use but had to determine that on our own. Whatever you do take lots and lots of picture before you remove the old harness. Routing the wires is as critical as getting them connected properly.

Building a high quality replacement harness takes lots of patience and lots of different materials for the various wire colors and sizes as well as all the different terminals plus all the bulb sockets. There are more circuits there than you realize and how they interconnect takes some finesse.

You keep saying that whoever did the 12 volt conversion disconnected all the gauges. Unless you have some type of aftermarket dash the only gauge that is voltage sensitive is the fuel gauge. You do need to put a "Runtz" resistor in that line ahead of the gauge. Most classic car supply houses sell a similar part. The ammeter does not run on voltage. The oil pressure and water temperature are mechanical gauges.

The heater fan motor will take some study to determine how to make it run on 12 volts. It might be easier to find a 12 volt motor that will fit that application.

Of course all the light bulbs as well as the flasher for the turn signals need to be 12 volt units.

Spend some time this summer researching the wiring diagram for your car and reading up on 12 volt conversions.

Good idea to stay with the 12V systems and alternator. There are not many wires on old cars and trucks. The wiring is very simple. The harnesses are inexpensive and easy to install. The common ones, which all use the same quality wire are Painless brand, Speedway auto, Ez wire. You probably only need a 12 circuit or so. The conversion is quite simple and as said some gauges are mechanical. You should get a new ignition switch and headlight switch. You will just tear out all of the old wiring and throw it away. Keep any and all connectors, clips, brackets, sockets, switches, knobs and any other associated electrical items. Just is case, until the job is completed. You will need a splice tool and a stripper tool. The DIY method you describe is no good. I have installed many harnesses and one time decided to do a DIY install. Never again. You want to be SURE you buy a prewired fuse panel type harness. ATO/ATC fuses. These are in the $150- $250 range. Voltage reducer resistors or a genuine Runtz will be needed here and there. The Runtz must be wired directly from the battery, NOT from the starter or any other place. None of this is anything to be worried about. You should highly consider abandoning the ammeter. You don't need it. Use a voltmeter. Most of the harnesses above do not support ammeters.

The expensive end of this is if you use American Autowire harnesses. They are very nice and have many many extras. Most of which you do not need. They are up in the $600+ range. Then there are the "original" specific custom harnesses using cloth covered wiring and original terminals and etc. Mostly for purists doing full out restore with 6V. They are higher priced than that. They really are not for a 12V conversion.

I would recommend Rhode Island wiring for your harness. It will be the correct type, fit, length of wires, etc., and usually cheaper than YNZ. I would call them and tell them that your car has been converted over to 12 volts and tell them what alternator and connector type it has. They can make it special for you and probably include the resistors where you need them or at least recommend which ones plus the instructions will show exactly where to put them. They do a superb job and get it done.
Most change from 6 to 12 volts because of the generator and cutout. Today with things like the Peterson hidden regulator staying with 6v and having the benefits of convenience of not worrying about an undercharged or overcharged battery, getting a new starter, alternator, putting resistors on things, changing out bulbs, etc., makes way more sense than doing a conversion to 12volt. Conversions are old school fixes for lack of knowledge and sheer convenience in my opinion as there is no longer a need simply to get more power for modern options or accessories. If you need music or something like that, today’s lipo batteries make for a tiny power pack to power those things and they can simply be tucked under a seat or what many do, in a radio box. I restore many cars and have not seen the need once to do a conversion. From cars, civilian trucks, to military trucks, they were built with 6 volt systems and ran perfectly fine with 6 volts for many years.converting to 12v has become a good excuse for poor grounds and undersized battery cables. 6 volt cables need to be much heavier and multi stranded compared to 12v.

This should be required reading for all car owners, especially those considering making a complete system change. It came 6, leave it alone, and clean it up and it will continue to work as designed.

I agree, stay with 6 volts! Going to 12 volts is NOT an upgrade! The only reason I see that you would want to go to 12 volts is to add airconditioning. I am not going to do that! If I have to have cooling I will take something modern.

Stay with 6 volts !! Why break into jail ??

I agree not to change to 12V just to change. My opinion is based on if a person is putting in a new universal prewired fuse panel harness and/or wanting to get rid of all the clap trap and wires involved with generators and voltage regulators....and of course V8 swaps. 12V is, in fact, an upgrade and a good idea unless you are that much of a purest. I cast no shade on a purest, original show car or nostalgia lover. In my opinion, electrical upgrade does not hurt anything. If you like cloth covered wire and generators, great.

For those wondering why convert to 12V as GM did in 1955: (trucks and cars)
1. No big huge cables required
2. You can buy a 12V battery anywhere.
3. Faster starting, especially in cold weather.
4. You can add accessories, winch, electric wipers, radios, bluetooth, bags, etc......
5. You can by bulbs anywhere
6. You can't get a jump start from someone without burning out bulbs and gauges.
7. Automotive is built around 12V systems. A standardized GM USA system since 54/55
8. Testing is built around 12V
9. Aftermarket is built around 12V
10. You can buy a 12V alternator anywhere and cheap. You can't buy a generator or Voltage regulator anywhere and cheap.
11. No Gen. polarizing or sticky VR contacts
12. Brighter headlights and tail lights, no need for relays
13. You can charge your cell phone
14. 6V takes twice the current/amps to get the same watts. If you have 50W hi beam headlights, they will draw twice as much current as on a 12V system. I.E. 100W (both headlights) is 100W/6V=16.7 Amps vs 100W/12V= 8.33 Amps. You can run out of amps on 6V. (dim lights, etc). Then you start band-aiding with relays, voltage regulator tricks or living with it.
15. May take a special harness to rewire 6V.
16. It's so easy and inexpensive.
17. There is no reason not to convert except to prove something...........I don't know what

18. You can also buy a new car or truck and get all the benefits of a 12 volt system without changing anything except dollars. Also have internet connectivity, drive at highway speeds, have many more people understand how to fix it, many "safety" features, etc.

In that case I am mystified why so many 12 volt crossed my service bay over the decades where the owner could not get things working properly. If I had a dollar for every time I heard "It must be something simple" or "but it worked before" I probably could have retired earlier. To this day I have never seen a converted car with every accessory and gauge working. This is a situation where a good understanding of Ohms Law and Kirchoff's Laws would save people a lot of money and trouble. If there is mainly 12 volt equipment to run, as in an engine swapped car with a 12 volt starter, 12 volt aftermarket gauges, 12 volt air conditioning, 12 volt stereo, etc. then 12 volts is a no brainer. On the other hand, if you have mainly 6 volt equipment to power, SPOILER: 6 volts works best. It still takes the same current to run those devices as it did before a conversion, and that implies those devices will be using twice the power they did before, and dissipating half of it as heat in a resistor or voltage regulator. You can't fool mother nature.

I feel for the OP because I have found myself in many messes like that, a few of which I created myself before I had enough experience to know any better. In the mid 80s I drove a 6 volt Nash for a winter car. I didn't have any starting problems, and it gets bitter cold here. Those 6 volt cars all worked when they were new, or the companies making them would not have been able to sell them for very long before people got wise. At the local cruise-in (when we still had one) many of the folks would say the same things you did in your post above. It's funny how none of those people take their cars on long trips. Today I daily drive a 6 volt car. I would rather drive than spend a bunch of time re-engineering the electrical system and I do know how.

As for the reason GM switched to 12 volts, my best guess is it was to save money on wire. Copper restrictions from the Korean War probably had something to do with that as well. GM switched in late 1952 by the way, for some 1953 models. They just didn't immediately propagate it company wide. By the time the change made it to Chevrolet and Pontiac for the 1955 models the horsepower race was well underway and there was no turning back. It is much easier to stuff extra turns of wire in a starter to crank a high compression V8 when that wire has half the cross sectional area.

As for number 13, there are readily available USB adapters that plug in to the cigarette lighter socket. USB charges at 5 volts, thus it works in a 6 volt car! I have powered my Garmin GPS as well as several different brands of cell phones using this USB adapter in a 6 volt car!

1. There is NO "re-engineering" involved in converting to 12V. No starter change. It's very simple.
2. I am speaking, as I said, of cars and truck owners doing a new harness and charging improvements. That would be older vehicles basically.
3. Buying a newer vehicle has nothing to do with my post.
4. 12V vehicles do not have more trouble than 6V, if that is what was meant by "things not working properly". The comment has no bearing on my post at all. We have been running 12V for 65+ years.
5. Spoiler: I am not talking about Ohm's Law. My headlight example is Watt's Law. It takes less current using 12V, for most components.
6. I'm sure there are many good memories about the 6V days.
7. Motors start better in winter with a 12V battery. There will be 6V and 12V motors that won't start well in winter. That's a story for a different post.
8. Copper restrictions had no basis for the entire auto industry switch to 12V batteries and components. There was no rationing or copper supply problem from 1949 thru the Korean war. The auto industry didn't change to 12V until the war was over.

From an original 1955 Chevrolet brochure: " A new 12V electrical system provides better ignition, faster cold weather starting and greater generator output".

There seems to be a lot of passion involved in this issue. I am a "original" type guy. Every older car and truck I have rebuilt/refurbished/refreshed/restored has been mostly original. I look for years for the right parts. I rebuild the old parts. I love the nostalgia. I grew up with all those cars and trucks. I am not a purist, but: I don't raise, drop, bag, hydraulic, chop, clip or pimp them. I think all that is cool. Just not my "bag". I don't smoke. I do drink beer. I don't use bias ply tires, I don't use tube tires, I don't use split rims, I like to put V8's in them sometimes, I never change the chassis or body or interior, I have indoor plumbing, I switch to 12V, negative ground. I don't use ammeters. I do have a cell phone but it's a flip phone. I add turn signals. I switch to alternator. I use
a new prewired fuse box universal harness. If a person is so stuck on nostalgia and wants to know they have 6V electrons and protons flowing thru their ride, that is "good". It's the way it was from the factory. There is nothing else "good" about 6V. I am just pointing out the truth for anyone who wants to
know. Urban legends, blog stories, aside. Sometimes I just get tired of folks advising to stay with 6V, as a "good" thing to do. Better than 12V it ain't. Said Yoda.

12V guys, you can come out of the closet.

6 volt or 12 volt - the actual voltage is irrelevant. It all works the same if all the corresponding correct components are used, installed properly and maintained. The underlying issue is many of these conversions are done by people who do not understand fully what they are doing and it results in a problematic system and much pain. Properly thought out and done with quality parts like the harness ChevyChic mentions as a starting point, a 12v conversion could work superbly on an old car.

Electrical systems seem to confuse more people than any other automotive technology so is one of those areas where the old adage "if you don't fully understand it, don't mess with it" applies.

There is no right or wrong in choosing whether to run 6v, 12v or even 24v, it's the execution and quality of the work that makes the difference like most things in life...

Yes, a new harness can be confusing for some folks. Together with 12V conversion and alternator. It's why I started an internet help business just for that.

Canadiantim hit the nail on the head !! Thanks for that.