Hi guys,
My 53 is bone stock except for a 302/C-4 and 9 inch rear end. It was an old farm truck. The previous owner removed all the wiring and stored it badly and it is completely ruined. I need to re-wire the whole truck. ..... It is a negative ground 12 volt harness. Can I get away with just running some voltage reducers on the gauges and switch the blower motor over to 12v? ..... What have you guys done when you stuff a later engine into one of these? My truck was originally 6 volt positive ground.
(sorry, an OCD moment) The harness itself isn't likely positive or negative ground, that's determined by which battery terminal & cable goes to the engine block/body of the truck. A 12v harness has smaller gauge wire than a 6v harness.
I like putting the battery ground cable to the engine block or head. It's a shorter higher capacity path for the ground connection of the starter, and you'll need a good sized ground wire from the block/head to the body of the truck. In the unlikely event the truck has an oem clock it is polarity & voltage sensitive. You'll probably want a 12v fan for the heater.
What year is the 302? Does the distributor have points inside or something electronic?
Ignition wiring to the coil can be confusing and you'll need a 12v starter solenoid. (photo below) Depending on the battery & solenoid location relative to the starter, the large battery & starter cables to/on the solenoid can be swapped no problem. But the wiring to the 'S' and 'I' terminals has to be as shown. Also, it makes a difference if the ignition coil with the 302 has an internal resistor or needs an external resistor. If the coil is marked 'internal resistor' the 'I' wire from the solenoid is not needed.
Here's a link to some good 6v to 12v conversion info.
https://www.ctci.org/gilsgarage/6to12.php
The oem 6v fuel & temp gauges and their sensors are not polarity sensitive, but the best/only chance they'll work correctly is to use original sensors. Due to the way the older gauges & sensors are made they can usually self-compensate for the higher voltage. A gauge voltage regulator isn't always needed.
If the original fuel gauge & it's sender are in good working condition they should be fine as is.
But, an older oem 6v Temp Gauge will not work with the '57 & newer (12v) temp sensors.
They aren't made the same way and won't work correctly with each other. If you can find an original 6v temp sensor and get it to fit in the 302 engine that would work. But, they are longer and have different size threads. The newer ones are 1/4 inch pipe thread and the older 6v style are 3/8's inch pipe thread.
I used a set of heads from a newer (12v) car on the engine in my (converted from 6v) '55 and had to re-thread the head to fit the older larger Temp sensor that matches the oem gauge in the dash.
In the photo below the larger temp sensor may actually be a one-year-only 12v '56 version,
IIRC the wire terminal/connector is different, but the overall size is the same as the earlier 6v ones.
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