The Stovebolt Site Forums The Shop Area The Electrical Bay 1946 Chevy 1/2Ton - New Wiring Harness

I'm getting ready to install a new wiring harness. Where do I begin? Is there an order of what I should connect first? Nothing extra on my truck. I am changing to 12v and have the harness for alternator. I think I have the first step completed - wiring harness through the firewall.🙂 Any helpful tips out there? Thanks!

Thanks to Dan (Gdads51) for posting a wiring diagram of my truck with generator. Also, Lee (46Sparky) emailed me a diagram of how they wired their truck. This will be helpful. I won't have a voltage regulator or generator.

You will have a generator. It's an AC generator (aka alternator) rather than a DC generator.

When looking at the diagram last night, I noticed one tail light was missing. But then I remembered the truck only came with one tail light back in those days. Adding the second light should not be difficult.

I have done two restorations, my '37 and '50 COE. On both, I started the harness placement before the gauge clusters were in place. After feeding the harness through the cowl from the engine side I fed extra into the cab. That way you could sit on the bench seat and make all those little connections with the gauges on your lap, a lot more comfortable than laying underneath the dash wondering if you are shorting out some connection. You still have to perform acrobatics to place the gauges but quite a bit more simple than the electrical connections. I am convinced they must have done this on the assembly line at the factory.

Kent

Looking for wiring help on which way to wire through the AMP gauge:

#1 - Wiring from the battery to starter, wire from starter to AMP gauge, through AMP gauge to ignition switch, through switch to ballast then to + on coil. Which side +/- should the wire from the starter connect to the AMP gauge? Or does it matter?

#2 - My wiring harness has a red wire from the alternator to AMP gauge. Does it matter which side +/-?

Is there a "Rule of Thumb" when wiring through the AMP gauge?

These are the two things I'd like to accomplish tomorrow. Thanks for any help.

Assuming a negative ground system, the rule of thumb is that the battery + connects to the starter and then to the ammeter +. All other loads and the charging system connect to the ammeter -. Once connected, turn on the headlights. The ammeter should show a discharge. If it shows a charge, swap all wires + to - on the ammeter.

So, do I need to connect the wire from the alternator to the ammeter? Will my stock ammeter take the increase in amps? (I'm converting from 6v to 12v with alternator.) I wasn't planning to connect that wire, but my wiring harness has the wire numbered and it says it connects to the ammeter.

Thanks for your input Bill. Much appreciated.

Assuming no added devices other than your second tail light, your 12v system will have less amps flowing than the 6v system had. As you add additional load you may find that the ammeter needle momentarily hits the peg just after first starting.

Another thing you will probably see is a lack of charging (and maybe a discharge) when idling, especially with the headlights on. Your alternator was designed for an engine that probably idled at 750-800 rpm. I don't know the proper idle speed for your '46, but my '52 GMC idles at 450 rpm. My 10si alternator does not put out enough power at that speed to keep the headlights from dimming. I don't have an ammeter, but my voltmeter drops to somewhere under 13v in that condition. Increasing engine rpm just a few hundred rpm jumps the voltage back into the high 13s+.

Thanks Bill! This morning I found the directions for the alternator setup. Mine has a DA plug so one wire to the back of the alternator and the other wire (exciter wire) goes to the ignition switch when in the ON position. So, I probably need the red wire in the wiring harness to connect the alternator to the ammeter to allow the battery to receive a charge. I think I'm good to get these connections in place today.

I just looked at a '50 Chevy truck wiring diagram, the closest I have to your '46. The only device connected to the ammeter + is the feed for the horn.

I have a '46 wiring diagram, but it has a generator and voltage regulator which I'm not using. It shows starter wire to ammeter and same terminal has wire to horn. The other terminal on the ammeter shows three wires to: Batt on voltage regulator, wire to ignition switch and wire to head light switch. I'm thinking I should connect the harness wire from the alternator to the same terminal on the ammeter as the starter and horn wire. That way the battery can receive a charge from the alternator.

The alternator should be connected on the ammeter on the opposite side of the battery (starter/horn) connection. So you can see if it shows a charge. The alternator has the regulator built in. The ammeter uses a shunt (a piece of heavy conductor) that carries the current, and the meter itself measures the voltage drop across that shunt. So no real concerns about current carrying capacity of the alternator.

Thanks Kevin! This is very helpful.

I don't know if my old wiring had any fuses? I was planning to add some. Any input on what size fuse I should be using and where? I was thinking: one between the starter and ammeter, one before the headlight switch and maybe one before the turn signal flasher. Not sure if all fuses should be the same or not. 10A, 20A, 30A - ?? I have an old diagram of a 6V system, but I have a 12v system with alternator now. My wiring harness did not come with any inline fuse connectors, but I have some now.

According to the wiring diagram HERE your truck had ONE fuse on the wire feeding power to the light switch.
Your plan on adding fuses would be good. As far as amp rating of the fuses, you'd need to add up the load on each fuse and install a fuse with a rating one size above what you come up with. Bulb info should have the amp draw of each fuse.

OK - Just found a formula to help determine fuse size. Wattage divided by Volts (12), then multiply by 1.5 to have a safety margin and get your fuse Amp size. I'll give this a try.

Update: I have most of the wiring completed, but waiting on parts for the left head light. I connected the battery last night and POP! My 30A fuse from the starter to the Ammeter was blown. I checked some wires around the dash, replaced the fuse and POP again? I got a little dejected because this wiring project has been pretty tough for me. I took another look around the dash and then in the engine bay. I had not connected the alternator yet since I wasn't running the engine and the wire from the harness was shorting out on the exhaust manifold. This morning I wired in the alternator and "exciter" wire to the ignition. Park lights, tail lights, head light, dash lights, turn signals,... all look to be working! I had to reverse the wiring on the Ammeter because it showed a charge when I turned on the lights. Now it shows a discharge. (Thanks for the tip Bill Hanlon.) So I'm feeling pretty happy now. I wasn't sure I'd be able to do this.

I'm glad to have guys like you around helping and sharing your knowledge. I was about to create another thread about my short circuit last night, but I came back to this thread and found everything I needed to help me resolve my issues. You guys ROCK!

It's always a great feeling when you find the cause of a problem and confirm that your solution was effective - great work!