The Stovebolt Site Forums The Shop Area The Electrical Bay Harness Upgrade in Stages?

('49 3600, 261, SM420, generator)

I've been reading all the excellent old posts on electrical harness upgrades and have 2 unanswered questions:

1. Texmo's excellent tech note https://www.stovebolt.com/techtips/electrical/electrical_upgrade/index.html references an earlier write-up on a '54 truck upgrade by Alan Horvath but alas the link has gone dead. Alan's '54 project writeup would be more relevant (for me) than Texmo's '63 project. Anyone aware of where one can find Alan's '54 truck writeup?

2. Interesting that all the projects and notes that I read are executed all at once. I understand the reasoning why, but has anyone done this upgrade piecemeal and have advice for that? The basic Classic Parts harnesses look like they come in three main parts. For those of us that can't sideline our trucks for an extended stretch, is it reasonable to do this upgrade in three separate weekends? Engine bay, then gauges and behind the Dash, then rest of the frame?

Good question and relevant. Some of the tech notes contain dead links and some contain some suggestions that could stand another look today. That has been discussed, by the way.

I've done it this way...in parts, that is. Once on a 1951 GMC and also around that same time on an MGB. Process is the same, no matter how you slice it, but I should add one observation. This approach works best if you have a firewall socket/plug. That is to say wiring under the hood leads up to a socket and wiring behind the firewall (internal wiring) plugs into that socket, leaving a natural staged approach.

You can find Alan's write up using the wayback machine. He used a store bought harness, so you may or not find it helpful:
https://web.archive.org/web/20191214114112/http://www.alanhorvath.com/54chevy/ezwire_day1.php

Before I give my spiel/answer, I would like to know your vision for your truck. We all like originality. There are some exceptions to that route. What is your aim as far as originality? Are you a purest, not wanting to deviate from original? Are you just trying to keep it looking original with some modern upgrades for safety and reliability? What is the overall goal, refurbish, restoration, refresh, preservation? Sounds like it is your daily driver, you only mode of transportation.

It is not feasible to do a piece meal wiring job using several separate harnesses. It is possible to get it running, or get lights, or get gauges, or get charging working but they all work off each other, sort of, and getting enough to be road worthy is doing them all. Don't worry about that. A weekend is all you need. I will explain once I get a feel for what you want as a truck.

My truck ('49 3600 261 SM420) is functional for light hauling/errand running. I like to keep it mostly looking original but am not a stickler for concours quality stuff, so I'm happy having a straight six 261 in it, but wouldn't go so far as to put a V-8 in.

I just can't ignore the corroded rat's nest of hacked up wires under the dash any longer. Is a weekend really all you need for an entire wire harness change? Engines I'm fine with, but electrons . . . that's like magic stuff . . . ;-P

Papa (or Mr. Disco), the main problem in rewiring is getting yourself under the dashboard. If you can manage that, you have much of the fight already won and with such a simple wiring scheme as the AD truck, I'd think a weekend might be plenty of time. The AD truck compared to one of today's vehicles is like comparing a see-saw to the Space Shuttle. If you get the proper firewall grommets, that can and will make your chore easier also. Personally I don't like wires that are spliced. Even if you splice them correctly, a continuous wire from start to end is best in my view. You might find some of those wires under your dash were added by previous owners and you might be able to do away with some of that wiring clutter.

I started studying electronics in 1957. Obviously, tremendous changes have occurred, but electrons are the same. The man who taught me said "It is a very good thing electrons are invisible. If you could see them constantly flying through walls, windows, concrete blocks, people, dogs and things you would be too scared to get out of your bed every morning."

Would you add a second fuse block for unknown future additions? My truck has the original fuse block (just the basics: lights and stuff). Maybe an extra terminal block in the cab and on the firewall for any future additions so I'm not trying to hotwire things off the headlight switch (like how they did the cigarette lighter!).

The Classic Trucks harnesses are not necessarily in three separate plugable sections. They are coiled in sections in the picture maybe. If a person is going to rewire a truck, I always recommend going to 12V. It's not any more work as far as harness install and just a little extra to accommodate 12V power. I always recommend a prewired fuse panel harness. There may be separate harnesses sold that can be connectorized to each other, or spliced, that could be done piece meal. That would be a bad idea. When converting to 12V it is better to also include an internally regulated alternator and you can keep the ammeter or install a volt meter. Also not a big deal to do. Your truck, and most trucks here, have very simple wiring. Nothing complicated. You only have two electrical gauges.


To answer your above question. In my scenario, you will rip out and abandon all wiring, fuses, generators..... and install a 12V battery and 10si alternator. It may or may not take more than two days. Lots of variables only you can control about that. A 12 circuit prewired Speedway Motors harness for $189 or equivalent will suffice. With two Classic Trucks part number 55-152.

More fuses won't hurt. It sort of depends on what you have. Common when the AD trucks were built were individual fuses (for things like radio, heater, etc). Not common at all were fuse blocks where additional things could be added. I'm certain you've seen these. Do you have the original wiring diagram? I might have it here somewhere. It wasn't bad work, actually but sophistication in production styles overtook it as few as 7 years later.

A prior owner converted the truck to 12v in the 80’s, but kept the generator. 12 circuits/fuses would be double what I have now so big improvement

Adding a new and expanded fuse block allows you to add other items easily. Example: I have A/C, HEI and an electric fan. And I have an alternator. These things use lots of juice. And please keep in mind relays. Your ignition switch was probably meant to handle a maximum of 10 amps of power flowing through it. Amps and voltage are two different things. For a long time I've told people to think of voltage as the size of your arm and amps as the strength of your arm. Mahalia Jackson had large arms. So does Arnold Schwarzenegger. Which one would you rather arm wrestle? Anyhow, using HEI or a strong electric fan can ruin your old ignition switch tout de suite. But with relays, you can send power to these things safely. Not to say you're going on a tear to find electronic things to add, but one never knows what may be in the future. I do have the 1949 wiring diagram. It is however very small so it would need to either be enlarged or viewed with a magnifying glass. But there were very few electric using "things" in there aside from lights, the coil, horn, etc. Just let me know if you want the diagram and I'll figure out how to get it to you.

Thanks Jon, I've got the shop manual and the factory assembly manual, both have a wiring diagram in them. Using relays is a good tip. I'll switch out to the electric fan one of these days and maybe A/C next summer.

Wow! a 12V generator and voltage regulator. PO was a certified purist.