74 Charger complete rewire

Has anyone here done a complete rewire of a 71-74 B body? Preferably a 74 Charger SE as that's what I've got. I've tried to find something like a complete step-by-step documentation as to how someone would do that but haven't had much luck the past several weeks.

Basically, I intend to replace the old alternator with a newer more powerful one, install a 6 speaker stereo system (likely running two amps, and 2 10s behind the rear seat in the trunk area), replace the ammeter with a voltmeter, install a tachometer in the dash, and will probably swap out some of the instrument panel lighting with some LEDs. So other than the stereo install (and possibly some LED lighting in the trunk) I will not be adding other electrical components. Not using electric fans, electric fuel pump, electronic ignition (sticking with the coil and distributor), etc. I also plan on doing away with the bulkhead connector and replacing the old eight cavity fusebox with something more manageable, relocating it to the glovebox or something similar.

I'm trying to figure out (as close to) exactly what wire I need, sizes, lengths, etc as well as how many fused circuits I need for the fuse box. I'd like to "simplify" the wiring so things are more tidy and (to me anyway) more sensible. I'd like to eliminate as much piggybacking as possible. I have this fantasy about every circuit having its own fuse and the only items on the same circuit would actually be related to each other (instead of having for example the dome light running off the radio fuse or whatnot).

I realise this is a major undertaking but it's something that seems to me to be worth the effort. So... are there any actual guides online (or in print for that matter) that offer more than "buy a complete harness from XYZ and follow the directions that come with it"?

I have done numerous wiring improvement on my 74 Charger and separated circuits. Added fuse boxes as well as relays for upgrades. Wiring has been challenging and actually finding schematics that match has proven to be impossible. Learn as you go and plan out what you want to do.

My car is not a show or collector car so I am going for safety and reliability.

64fury74charger said:

I have done numerous wiring improvement on my 74 Charger and separated circuits. Added fuse boxes as well as relays for upgrades. Wiring has been challenging and actually finding schematics that match has proven to be impossible. Learn as you go and plan out what you want to do.

My car is not a show or collector car so I am going for safety and reliability.

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So if I understand you correctly you basically rewired the vehicle section by section or part by part over time? Where did you start?

I have done a number of complete rewire jobs, most recently a 69 Ply Wagon and a 73 Cuda before that. I am not sure what your intent is with regards to the harness, are you wanting to modify the stock harness, get a different harness or something else.

While it is true that there are some things within the stock harness that draw/provide power to multiple things I don't know how you would add more circuits without a new harness unless you want to use a power distribution block which is certainly possible. Personally I would start with a new harness, modern harness pretty much have single circuits powering all of the system. You can get a cheap one (generic eBay) and then wire the car yourself or get a better one (Kwik wire) and wire it yourself but have a better system.

As to the sizes of the wires, look a stock diagram, they give you all of the sizes there (at least they do up to 73). I tend to up the wire size a bit when I do them just as insurance.

No need to replace the amm with a volt
You can uograde your alt just installing an alternative path from alt to the cab.

Once alt is upgraded, you can make a custom power junction point to feed from there everything you want. Alt output be calculated based on the accesories will working at the same time.

Alt is the main power source, not the batt.

Batt is is the cracking power source and an ocassional backup reserve load for the rest.

I have the 74 diagram but without the the full legend info. The best for you is get the FSM... CDRom or printed. Unfortunately the 74 manual is not uploaded anywhere yet. And no, is not the same than earliers, ALTHOUGHT for the basics, earlier will be helpfull too.

From a 74 daily driver owner to the other. Other than if your wiring is hacked up, you won't need really a big job neither investment to make the stock wiring fully trustable with just minor upgrades and fixes.

Right now, I keep blowing the fuse in fuse cavity 4, which feeds the tail lights, the instrument panel lights, and a few other things. My stop lights work, blinkers work, headlights work, brights work, dome light works, but no tail lights, side marker lights, or dash/instrument panel lights.

Looking up under the dash, it looks like a mess! Previous owner had a couple wires just snipped off (not even taped), obvious patch replacements (using different wire colors), etc. A couple days ago the car wouldn't even try to start. Thought my starter was done for but I fiddled around under the dash and wiggled the fuse block (put it back on its mounts) and pushed a connector plug up out of the way and lo and behold she starts right up.

So obviously there are some gremlins running around up in my dash.

I have repaired a number of systems like you are describing and it is time consuming painful work, personally I would replace it with a new harness, perhaps not a stock one but new nonetheless.

Rebel74 said:

So if I understand you correctly you basically rewired the vehicle section by section or part by part over time? Where did you start?

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Some time ago I had intermittent starting issues where turning the key got absolutely nothing. Would work fine for weeks and then crap out. Plus my car had the seat belt interlock along with the “emergency starting button “ on the firewall and both had been previously butchered and not fully taken out of the system.
Then I pulled the dash just to have a good look and that was not pretty either. At that time I was not able to take the car out of service as it was my main daily driver, so I wired in a push button to the relay for the starting issue which was a major improvement and used that until the 318 was swapped out for the 400 a few years ago.

I put a fuse box over on the right kick panel that handles the heater blower, radio and small amplifier. I have another fuse box and 8 relays in a small box where the battery used to sit. 3 relays are in use now with plans to use a couple more soon. Provides clean 12 volts for ignition and the Sniper efi.

I ran a double loop of 8 gauge wire from the alternator stud to both the amp gauge wire and the relay on the firewall. Put a 40 amp fuse on the other side and bypassed the firewall connection completely. This was the result of low voltage even with new alternator and regulator. After this update voltage is 14.5 even at idle. There is plenty more but I am going to let you digest this and go from there. I don’t have access to the pictures right now but will try to post some pictures later.

I have driven this car on trips and daily and so far zero electrical issues. Hope this helps you.

I went with a new wire harness kit from American Autowire on my 71.
They have a kit that is specific to 71-74 Chargers and includes everything from the fuse box to the light connectors. They have sub harnesses for the dash (after market gauges or original dash), new headlight switch, new hi/low beam switch, all the connectors and pins needed are included as well.

Every wire is labeled and the instructions were spot on.

The only other things I had to buy were the AC sub harness (comes with non-AC sub harness) and good set of crimpers.

I put the American Autowire update harness in my '71. It's a very nice kit. My only complaint would be that they went with their own color scheme on the wiring, even in places where it would have been easy to use the factory color scheme such as the front light harness. For mine, since I had an almost brand new front light harness, I just replaced the AAW front light wiring with the wiring from the Year One harness that I already had. It was simple enough to pop the AAW leads out of their bulkhead disconnect and insert the leads from the YO bulkhead disconnect. I did have to find a male Packard 59-series terminal to complete the switchover but I don't remember if that was for lighting or ignition. I switched to an HEI distributor and a one-wire alternator (AAW instructions call for a one-wire alternator) so my firewall-mounted ignition box, voltage regulator, and ballast were no longer needed. Those holes were welded up and painted over. If you go the AAW route, do yourself a favor and buy good crimpers.

you would be suprised how easy is fix a wiring system if you really care about it.

Nacho-RT74 said:

you would be suprised how easy is fix a wiring system if you really care about it.

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I've been frying my brain to figure this stuff out.

I broke down and ordered an actual 74 Charger service manual set so I can at least quit trying to guess how accurate the 73 manual I have is. I'm basically just going to wait until the new manual set arrives so I can see what's actually relevant to my car and go from there.

I'm still trying to determine where to start - the "headlamp relay" mod? Or start with a new fuse block and work outward from there? I think I'm probably over-analyzing things too much.

Rebel74 said:

Right now, I keep blowing the fuse in fuse cavity 4, which feeds the tail lights, the instrument panel lights, and a few other things. My stop lights work, blinkers work, headlights work, brights work, dome light works, but no tail lights, side marker lights, or dash/instrument panel lights.

Looking up under the dash, it looks like a mess! Previous owner had a couple wires just snipped off (not even taped), obvious patch replacements (using different wire colors), etc. A couple days ago the car wouldn't even try to start. Thought my starter was done for but I fiddled around under the dash and wiggled the fuse block (put it back on its mounts) and pushed a connector plug up out of the way and lo and behold she starts right up.

So obviously there are some gremlins running around up in my dash.

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Sounds like a bad ground(s), or frayed/cracked powered wiring going to ground.

remove the wiring, work it on a bench... is a surgery game. Isn't a game even dirty o greasy!!!