One of my goals is to feel good about taking the car for medium length trips, weekend sort of things, a few hundred miles each way. Part of feeling good about that is making sure that I don't need to pack oddball parts like ceramic fuses. They don't have any unique characteristics and just make things complicated when the whole world has standardized on blade fuses eons ago. 1976 is when they were introduced, says Wikipedia. That's long enough.
So how do we get modern blade-style fuses into an old car? Fortunately there are companies making replacement fuse panels which are 1:1 replacements. The panel I bought even has built in headlight relays. #Winning
Here are the new panel and old panel plus my semi-janky headlight relay setup. A new panel with relays was always part of the roadmap so I knew this was a temp setup. The current relays are bolted to a sheet of aluminum that is tie-wrapped against a piece of insulating foam. The wiring is all soldered and shrink-wrapped and then wire tied. It's not beautiful, but it is very solid. And I did not drill any holes. Ground runs to the chassis bolt all the way to the left (pic), and hot is connected at the battery clamp. (the 12ga red wire headed up from the battery in the pic).
In general, auto wiring is generally very simple and repetitive. You loop from + on the battery to ground (chassis or - on the battery) with some device or system in line. The car is really just a series of loops in parallel. The hot side (top) of the fuse panel is where power enters, and then it leaves the fuse panel from the bottom to go to the load; whatever it is we are operating. Fuses are there in case something goes wrong and that load draws too much current - without fuses we could fry our wiring. All wire has a current rating that comes down to how much heat it can take, which is a product of the current it is carrying plus if it is out in the open or tied up in a bundle (where it can't easily get rid of heat). And take it from someone who has been there; setting your dash on fire on a hot date is not a good look.
For the curious
https://www.engineeringtoolbox.com/amps-wire-gauge-d_730.html
For a next level understanding, think about it using Ohm's Law. Ohm's law states that voltage is equal to current multiplied by resistance, or V=I*R. V here is nearly always going to be 12 - our battery. So I (current flow) is determined by the resistance of the load. If the load has a short circuit, R may drop to close to zero which will maximize I, because V is not going to change, and I*R always has to equal 12. Car batteries can deliver a LOT of current. Usually in the hundreds of amperes. Your car has a lot power on tap. You can weld with it. Please don't test this.
Process
First we need to compare old to new and make sure it all ties out. I am also referencing them both to the diagrams in the Bentley manual. There are extra spots on the old panel - they are just extra connection points because of the number & size of the wires. I need to make sure everything will fit. There are also shorting links on the old panel; those links are indicated on the circuit board on the new panel and do not need to be moved over. I double checked the links with an ohmmeter. They are all there.
If everything ties out on paper we can begin our work. A place for every wire, and every wire in its place. That is the goal. Step one will always be disconnecting the battery.
Next, the panel mfr recommends tie wrapping new on top of old (only after disconnecting the battery!) and then moving wires over one at a time. I am going to be a bit more OCD; I am going to print labels for every lead as well as take a bunch of pictures. Then I will move them over. Slow and steady wins this race. I am red-green color blind so the pics will be of limited good. I need to be more organized.
It's only 21 connections on top and again on bottom. The answer to the universe, 42! Just go one at a time, be very careful not to lose any wires behind the board, and you should be fine.
Step 1: "The labelling is the hardest part..."
We have chosen to label for a few reasons here. First is I am RG color-blind. Photos and diagrams will only do so much good: I need more. Second, we need to spot problem areas ahead of time. For example, we have 21 positions top & bottom on the new board. But the old board has extra spots, and does not follow any kind of "one wire per hole" convention. It's a bit of a free for all. Labelling everything forces me to ID the wires at each position on the panel and ID all of my issues ahead of time. I started from the RH side, with position 21. I made the top row "prime", but my label maker doesn't have a single quote so I used an asterix. Net net, label 21* is the top, 21 is the bottom.
15* & 16* are where the leads go to & from the headlight relays (hence the splices) 14* has no connection because it is bridged to 15* to operate the headlights.
Exactly 42 connections, on paper. Read into that what you will.
This is an example of the "fun part". The first 3 positions (going L to R) look ok, 1 position with 1 wire. ok. But look at the 4, 5 & 6. They are shorted together to make one big terminal for 5 wires. (and shorted to 2 & 3 as well by those copper straps). There are several spots on the panel that do this just to make room for all the wires.
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