How many amps are too many?

[Pep48]

I'm installing a 12v alternator, Negative ground system, in my 48 coupe. I'm planning to connect the output wire to the stock regulator's B terminal (F & A wires removed).

 

The alternator is a GM 12si rated at 78 amps. I'm installing a 100 amp fuse in the output line.

The only added accessories will be a stereo (10 amp max) (no amplifier) and H4 LED headlights (approx 9 amps total for both headlights). = 19 total amps above stock.

 

Will this fry my stock ammeter gauge?

Thanks for your input.

[Los_Control]

37 minutes ago, Pep48 said:

I'm planning to connect the output wire to the stock regulator's B terminal (F & A wires

Why?

 

You are converting 100% to a totally different system .... why would you want to use any of the old charging wires that were put in place to work opposite of what you currently have.

 

No expert here, but not my choice.

You will be fine, you actually want to cut into the charging system after the amp gauge .... 78 amps going through your amp gauge could start a fire.

Pretty sure your F& A wires cut in before the amp gauge ...... no idea but I think you better spend more time thinking about it. I'm replacing all my wiring and the power wire off the alt goes after the amp gauge .... then a volt meter is more functional and included in my wiring diagram.

 

I'm just saying, the typical 48 cloth covered wiring needs to be replaced .... if your wiring has already been replaced that is fine ..... just creates issues if you are switching grounds and such from positive to negative ..... you sure do not want to run a positive wire into a ground wire.

[Sniper]

The ONLY load that goes thru the ammeter is battery charging and the horn in the stock configuration.  Nothing else.

 

Your headlights and stereo, assuming you didn't wire them direct to the battery, should never go thru the ammeter with the engine running.

 

Where did you wire your new stuff?

 

Also, remember that stuff draws half the amps with twice the voltage. 

[Sam Buchanan]

Your alternator fuse needs to be sized according to the current load your wiring harness will tolerate before failing, not according to the potential output of the alternator. The fuse is to protect your car's wiring in case an internal short occurs in the alternator (quite unlikely but protection is a good idea).

 

I don't know what that number is since I don't know details of your wiring architecture but 100a is no doubt way too big.

[tonybiel]

Repeating some of what was already said:

 

Your conductor must be sized properly for the load, then size the fuse to protect the conductor from overload.  On my 51 Dodge, I wired the alternator directly to the battery cable with a fused conductor.  Using an ammeter and wiring to the dash is old technology and a fire hazard.  I kept my ammeter in the dash just for looks, but it is not wired in to the system.  Add a voltmeter somewhere.

 

I wanted to stay as original as possible, but in my opinion a 12v system with an updated wiring harness is a must.  You can purchase a complete universal harness with multiple fused circuits at a very reasonable price.  Your fuse panel is powered from the battery terminal.  All conductors are then protected with the proper size fuse.