Amp Capacities?

[FY1Cuda]

When we were putting together our car, the 12ga red wire that feeds to the ammeter was toast so we replaced it.  We put an inline 40 amp fuse in the wire because we didn't have the fusible link anymore.  Here's my question: Does anyone know the amp rating for the original fusible link (and does a 40 amp fuse do the job)?   Related to that, I know that for house wiring, particular wire gauges are related to the amp capacities of the circuits, like 12ga wire on a 20 amp circuit and 10ga wire on a 30 amp circuit.  For a 12v car system is there a rule of thumb for wire gauge and the fuse that protects that wire?

[Bullitt-]

http://www.engineeringtoolbox.com/amps-wire-gauge-d_730.html

American Wire Gauge (AWG) Length (feet)    Current (amps) 5    10    15    20    25    30    40    50    60    70 15    16    12    10    10    8    8    6    6    4    4 20    14    12    10    8    8    6    6    4    4    4 25    14    10    8    8    6    6    4    4    2    2 30    12    10    8    6    6    4    4    2    2    2 40    12    8    6    6    4    4    2    2    1    1/0 50    10    8    6    4    4    2    2    1    1/0    1/0 60    10    6    6    4    2    2    1    1/0    2/0    2/0 70    10    6    4    2    2    2    1/0    2/0    2/0    3/0 80    8    6    4    2    2    1    1/0    2/0    3/0    3/0 90    8    4    4    2    1    1/0    2/0    3/0    3/0    4/0

As for the fuse you will be ok as long as there is no surge, the problem with regular fuse's is they blow easily...a slow blow fuse would be better, fusible links available at any auto parts store.

[FY1Cuda]

Thanks for the info and link.  I thought you might be the one to respond because you're pretty savvy with electrical issues.  Thanks again.

[Moparal]

electrical, I was hoping he'd drive over and help with mechanical

[73EStroker]

You need minimum 8AWG wire for your ammeter. And bypass the firewall connection plug if you are not worried about the originality. IE drill out both sides of the plug (for the battery to ammeter and ammeter to alternator connections) and bring the wiire to the inside of the car and use 2 crimp lg rings on each pari of wires. Use 10-32 bolts and nuts to join, cut the bolts short and tape with GOOD PVC tape not cheap crap from department stores. This way if you have to disconnect the firewall plug you simply undo the tape, bolts and voila!

[FY1Cuda]

Thanks.  We have a 10ga wire in there now and have the headlights on relays, but we did blow the 40 amp inline fuse the other night by starting the car with the lights and heater on, so that was why I was wondering about how much current was going through there.

[73EStroker]

Something is wrong if you are blowing that 40A fuse. The starter basically has no fuse protection as it goes from battery + to the starter solenoid direct. Have you replaced the starter solenoid yet? The circuit that drives the starter has some fusible link protection so it may be half shorted and that would cause a larger current draw. I know everything costs money folks but with electrical, unless you know the history of the car or have owned it for many years, then the electrical is usually always suspect. These machines are nearing 40 years old and some times the electrical is best to be replaced if it gives trouble. But make sure the part you are replacing is the faulty piece. So to do that I suggest that you take the  solenoid wire off the starter relay, wire it through a temporary fuse (15A should suffice) then with that wire touch it on the main terminal contact. Sparks will fly but not too much and the starter will spin so be careful. If it blows a 15A fuse then there is your culprit. If not start by process of elimination. Excellent that you run the lights through relays. I did mine and boy do they hurt at night but they are Hella H4/H1s.

[FY1Cuda]

Thanks  for all  the input.  I was also surprised that the fuse blew so I will look into it further.  The solenoid is on a rather recently rebuilt mini-starter, but your suggestion to eliminate that source of trouble seems easy enough to do, so I'll try that when I find time to play with the car.  In the meantime I think I'll take Bullitt's suggestion and put in a slow-blow fuse. Thanks again to both of you.