There is a recent post on ammeter bypass i have watched and read Daniel Sterns article on relays. I understand the wiring concept however get lost in the flow, and maybe that's wrong. I have a 68' 300 with an electric fan with two relays powered directly from the battery with a temp switch turning on/off. If the fan is drawing say 30 amps when on from the battery, is the replacement power not still flowing through the ammeter if no changes made from alt to firewall to ammeter to battery? How do the relays reduce the flow through the ammeter? Same example would be with a headlight relay. I guess the question is, if power taken directly from battery by other sources, how does that reduce power replacement through the ammeter?
First, glad to see the correct term "ammeter".
Let's understand (although I think you do), that the relays for the headlights are added to reduce the current running through the connections at the bulkhead, switch etc. and to have less voltage drop because of shorter, more direct wiring. Using a relay for the fan is done so any additional wiring (let's say a dash switch) also has less current running through it.
Let's forget about the fans for a minute.
So, in answer to your question, yes, the charging current is still running through the ammeter. Adding headlight relays keeps the current down running through the wiring, and that's good, but it doesn't change what runs through the ammeter. But that current also hasn't increased, and as long as everything is in good condition and tight, all is good.
Now add the fans. Yes, the amount of current draw from the battery is increased. The battery will now need more charging current, but you have some limitations. One is alternator output. It's only going to charge what it can. So, in theory, all should be good, but it is going to be taxed. But will the stock, low output alternator be enough? Probably not. So you put the higher output alternator on that's capable of charging the battery a little faster and now you are pushing the stock wiring and ammeter past its limitations.
If you are adding fans, yes, good idea to do the bypass. Adding fans AND increasing alternator output to make up for them? Yes,
do the bypass, no question. Adding just a larger alternator with nothing else? Yes, good idea to do the bypass, but remember that it only puts out what it needs to (I had a girlfriend like that once) and unless you've added more draw (like amplifiers or fan) it's not charging any more than your stock alternator did.
It is my opinion that the so called ammeter fires are actually bad wiring or loose connections (especially at the ammeter). Doing the bypass is still a good idea for many reasons though even when staying stock. It does take the load off the wiring and connections.
