ignition switch confusion

good info...   so did you add one to your 76? when I ordered mine Vince ask me which one I wanted and I didnt know what to tell him. so we went with 40 since it was cheapest and the alternator didnt make but 35-37a anyway. I guess 40 is better than none

Because it wasn’t stated explicitly, it should be noted that the purpose of the breaker is to protect the WIRING (breaker size should be nominally lower than the current handling capability of the smallest wire attached to it). If - and only if - the wire size has been appropriately selected to handle the full rated output of the alternator, should the breaker be similarly sized.

In this case I suspect it is... but to omit the wiring from this particular conversation seems just a tad short sighted.

Having read this info I'm a little worried.
I put a 1 wire AC Delso alternator in my 85 SN. It's 105 amps if I remember right. I hooked it to the orange wire and left the excitation wire unused. It seems to work great but it sounds like I could melt some wires.
I have no extra electric loads in the boat than it came with when it was built I bought the alternator because it was cheap and easy to hook up, not to supply lots of power to anything.
What can I do to protect my wiring?

TRBenj wrote: If you want to mimic the factory set up, then you would want to upsize the wire between the alt output and main engine breaker (unprotected side) such that it can handle the full rated load of the alt. I’d have to check the chart, but this may be an 8awg or even 4awg for 105a. The main engine breaker is there to protect the other side (10awg wire feeding the dash) and shouldn’t be changed.

I've done just that with a Delco alternator, it works just fine moving the alternator feed to the upstream side of the main breaker with bigger wire instead of the dowmstream side where it was originally hooked up by PCM.

Doing it this way, 40 plus amps anywhere on the "protected" side causes a breaker trip and takes the battery and the alternator out of the picture at the same time,unlike the PCM way which takes the battery out but must depend on the alternator cooking itself if you have a fault is between the 40 amp breaker and the 20 amp breaker on the dash.

You might figure a fault there is pretty unlikely but..............sheet happens

Which naturally leads to the question of why they did it the way they did

I've also taken a different approach and left the PCM wiring as is, including the 10 gauge Orange alternator output wire and put a 40 amp fuse on the alternator output terminal with the Orange wire hooked to that.

Basically turned the higher capacity alternator into a 40 amp alternator with that fuse, but the boat has no extra loads and won't ever use 40 amps unless there's an electrical issue like a ground affecting the system.

Like Cyclone who asked the original question I got the higher amp alternator because it was cheap and easy to install And Delco parts are readily available most anywhere and they're easy to "fluff and buff"   

Both ways have given no issues    

Tim

I'll let ya' in on a little poorly kept secret...............There's a really good easy to follow diagram floating around out there for the mid 80's PCM engines.

It was made by some guy with the same name as you

You should get paid a royalty fee every time it gets used

Twice the fee when it shows up on Team Talk,

Three times the fee when it's used for an Indmar 351 reference

I took the easy way and installed a 40 anp fuse and all seems well. Thanks for a good discussion of things that could be done.