Electrical System Updates

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This web page is about restoring/resto-rodding a 1950 Ford F-1 pickup, and is one of a series of articles documenting the project. I am providing this in the hope that it is helpful to fellow Ford truck owners, but beware that there are many ways to accomplish the same goals... I have only shown one way. Also, keep in mind, that my comments are specific to this year, make and model, and should not be generalized. Feel free to drop me a line if you see mistakes or need more information, but please understand if it takes me a while to respond. To go back to the main project page click here.

Our Plan

Our plan was to convert the truck from 6V+ ground to 12V- ground.

First Rewiring

When I was given the truck, it came with a new wiring harness, which we were told was from JC Whitney (P/N 3211). I completely re-wired the truck in July 1992 using this harness (see wiring diagram at top).

Second Rewiring (Converting from 6V postive ground to 12V negative ground)

Unless you are doing strict restoration, you will want to convert the truck from 6-volt positive ground to 12-volt negative ground. If you don't convert to 12V negative gound, you can't even consider electronic ignition, air conditioning, electric fan and fuel pump, or even get a jump start! Converting the truck from 6-volt positive ground to 12-volt negative ground was quite easy since there are no fancy electronics or computers involved. The gauges work on resistance, so changing polarity is not an issue. If you are using the factory gauges and sending units, you will need to install a voltage reducer. There are 2 kinds of voltage reducers to choose from: the kind Ford used from 1957 up through the 70's and Runtz style. Most people (including myself) are not aware that Ford continued to use 6V gauges after the switch to 12V in 1957... all the way up through the 1970's. They accomplished this by adding an Instrument Voltage Regulator (NAPA P/N ECH IR1), which has a set of points that open and close (about once per second). The voltage is not actually reduced, but switched on and off, the net result being that a 6V gauge reads correctly when fed 12V. The second kind of voltage reducer is called a Runtz voltage reducer (Speedway P/N 91064101). It works in basically the same way except it uses transitors to switch the 12V feed on and off. Neither of these is a resistor, which would affect the gauge reading. Do not use any kind of voltage reducer on the ammeter. See the Finishing Touches section for how to eliminate the ammeter in favor of another temperature gauge and use a voltmeter instead.

The advantage of the Ford-style voltage reducer is that you only need one to feed all the gauges, but the disadvantage is that you'll notice your gauges "bounce" a little bit. This happens because the Ford-style voltage reducer cycles the power to the gauges slowly. On the other hand, Runtz reducers cycle much faster, so the gauges do not bounce, but you have to use one Runtz per gauge because the Runtz reducers cannot handle much current. I tried it both ways... they both work... but I ended up sticking with the Ford-style reducer - the wiring is a little cleaner.

If you don't want to re-use the factory gauges, there are a couple of options. You can send the instrument cluster and have it converted to 12V with modern movements and an electric speedometer, keeping the original look (cost $2000-$4000), or you can buy a billet instrument cluster panel and use modern round gauges (cost with senders, less than $1000). This option is less expensive, and you have many choices of gauges, including modern or classic look, but so many people choose this path, its kind of boring.

As mentioned in the article on the engine rebuild, we had the factory generator rebuilt and converted to 12V and used an external voltage regulator. The problem with this is that generators don't put out much at idle or when they are hot. A better solution is to switch to a 12V alternator. There are 2 ways to do this. First, you can use a modern 12V alternator and buy (or make) a custom bracket and change the pulley to wide belt (or change everything else to a narrow belt). The most common way to do this is to use a Delco alternator, and mounting brackets are readily available. The disadvange is it does not look stock. The second method (the one we used) is to buy an alternator that looks like a generator. Powermasters makes a kit for Ford flatheads, which includes a modified (but factory looking) mount, an internal voltage regulator and 1 wire hookup. Speedway has these for early and late flatheads.

The wiring harness installed in 1992 was in excellent shape, and since it was designed for 6V, it did not need to be replaced after converting to 12V because the current load is halved. However, we added an electric cooling fan, air conditioning and turn signals, and while we could have made due with the wiring harness, I decided to replace it with a modern harness. The main advantage is safety - the factory wiring had only 2 fuses!

I purchased the American Autowire Highway 15 wiring kit. This kit has 15 fused circuits, horn and signal relays, and headlight and ignition switches. The wiring is color coded and labeled, and has all appropriate terminals installed (for headlamps, etc.).

Installation is relatively straighforward using the supplied instructions, but if you are not comfortable with wiring, you should hire someone to do this for you. One area that required some changes was hooking up the turn signals. I added turn signals (Mac's Antique Auto Parts, $57), but this kit includes its own 3-post flasher. I wanted to use the flasher built into the Highway 15 kit. This was not difficult to figure out (combining the 2 wiring diagrams and figuring out how to hook up the signals to a 2-post flasher), but in doing so, the light on the turn signal stalk does not flash with the signals. In order to make sure that I don't drive down the road with my turn signals on (there is no self-canceling mechanism), I installed a "loud flasher" (NAPA LF-12).

Relays

Relays should be used for all "high load" electrical devices. The American Autowire fuse box inlcuded built-in relays for the horn and head lights. I added relays for the fuel pump, cooling fan and air conditioner. Relays are simple to install, and reduce the load on the ignition switch. Most relays are rated for either 20A, 30A or 40A, and can be picked up at most auto parts stores or from Speedway and Summit, among others. But beware: all relays are not all created equal... and some are only for "interior use". Most automotive applications will need a SPDT relay. I recommend Hella relays, and waterproof ones for anything not in the cab.

Hits & Misses

The American Autowire Highway kit is first rate quality.

Time Line

July 1992 - rewired truck with factory style harness
December 2010 - complete custom rewire using Highway 15 kit

Last Updated: Monday May 30, 2011