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Author
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Topic: shorting out ampmeter
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rexbd
Journeyman Posts: 26
From:
Registered: Jan 2005
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posted 09-19-2005 08:20 AM
 
Everything is now working and the car is on the road after a year and a half restoration! One remaining problem is I have shorted out two ampmeters and don't know why. Everything else is working great. Any ideas. I did not replace my constant voltage regulator, could that be the problem?
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ciscokid
Gearhead Posts: 182
From: Ooltewah, TN
Registered: Jul 2001
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posted 09-19-2005 09:59 AM
What do you mean by "shorted out" the ammeters? How did they fail, by pegging in one direction or the other? Burning out and smoking? Just not working at all?The constant voltage regulator is not involved with the ammeter circuit. The ammeter circuit is very simple, but also very touchy. In the early Mustangs the ammeter measures the amount and direction of the current flowing through a portion of the heavy black/yellow wire that connects the alternator to the battery. One side of the ammeter is connected to the battery side of the starter solenoid (yellow wire). A violet wire (for '67) coming out of the alternator wiring harness connects to the other side of the ammeter. The ammeter is in parallel with a segment of the black/yellow wire. What happens is that a small, proportional amount of the current flowing in the wire also flows through the ammeter. The ammeter itself cannot handle a lot of current, which is why a small amount is shunted through the meter while the majority flows in the black/yellow wire. If, for some reason, the ammeter is not wired properly, or there is a high resistance in the wiring of the black/yellow wire, then an excessive amount of current can flow through the parallel ammeter and can burn it out. Another thing that can happen is if you were to disconnect the black/yellow wire from the starter solenoid and left the yellow wire for the ammeter connected, and then did something that draws a significant amount of current, like turn on the headlights, then all of the current will go through the ammeter, which is sure to fry it. It is very important that you have the right alternator wiring harness for your car, and that is is in good shape and installed correctly. If it is a replacement it needs to be from a quality manufacturer. The wrong harness can shunt an incorrect amount of current through the ammeter. Never disconnect the black/yellow wire from the starter solenoid without also disconnecting the yellow wire for the ammeter circuit too, or your asking for trouble. Just stepping on the brake pedal could fry the ammeter.
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rexbd
Journeyman Posts: 26
From:
Registered: Jan 2005
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posted 09-19-2005 10:09 AM
The thing went up in smoke as soon as I turned the key. I know I am wired up properly on the back of the gauge since it is stamped right into the metal. I wonder if I have a wire in the wrong spot on the solenoid? I will look at how that is wired up tonight. Appreciate the help.
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ciscokid
Gearhead Posts: 182
From: Ooltewah, TN
Registered: Jul 2001
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posted 09-19-2005 12:52 PM
If it went up in smoke then it has way too much current through it. You can't hook it up in a way that would damage it, if the wires were reversed it would just read backward, showing a discharge condition when it was charging and vice-versa. You can hook the wrong wires to it, or the other end of those wires could be connected improperly. It's only two wires so it should be pretty easy to check.
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blackford
Journeyman Posts: 76
From: Corona, Ca
Registered: Jan 2004
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posted 09-19-2005 07:42 PM
I don't know what car you have so i'll tell you how a '65 works and most likely yours is similiar. The ammeter circuit is in parallel with the circuit between the alternator output and the positive battery terminal (a heavy 10 gauge black wire on my car). It carries only a small fraction of the current while the other circuit carries most of the current. If the other circuit is open or the ammeter is hooked to ground, it will fry. My ammeter only takes about 3/4 amp to peg one way or the other. They have been known to get burned out when people jump batteries, etc. so I put a 3 amp fuse in the ammeter circuit to protect it.------------------
Tracy Blackford
'65 "Black" ford FB, 331 with H beam 289 rods, KB322s, fully prepped 351w heads, 282S cam, C-4 auto, 3.50 9" posi. Many Suspension and handling mods. 4.5 year restomod project completed in May '04. 313 RWHP @ 6300.
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DidgeyTrucker
Gearhead Posts: 1813
From: Greenbrier, TN USA
Registered: Oct 99
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posted 09-19-2005 10:40 PM
Wow, Ford really does/did build "tough" trucks. The optional ammeter on the '65/'66 Custom Cab F-100s DOES carry all the current.Tracy [This message has been edited by DidgeyTrucker (edited 09-19-2005).]
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rexbd
Journeyman Posts: 26
From:
Registered: Jan 2005
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posted 09-20-2005 07:29 AM
Ok, I definately have a screwed up wiring situation. For back ground, this car was originally a small block no tach vehicle I bought as a baslet case and no motor. I put in a 390, 4 spd and stayed with original no tach wiring. I bought the big block alternator wiring harness but it wouldn't hook into the wiring loom as the connectors were different so I bought a different alternator connector. Here's what I noticed last night when I went back throught the wiring.The wiring is layed out as follows: Alternator:
large black wire hooked to BAT terminal on alt
Orange wire hooked to FLD terminal on alt
Black/Red wire hooked to gound. Alternator wiring to Loom wiring:
Female black/red to male black red in loom
Male large black to female large black on loom (this is the wire that is getting hot)
orange male to white female in loom. Volt Regulator:
White to F terminal
Green/Red to B terminal
yellow to A terminal Here's what I noticed: The schematic shows the middle wire from the alt harness should go to the volt regulator, mine doesn't, I think I have it connected to the ground screw along with another black wire and a black/red wire. The schematic shows that the bat terminal wire should go directly to the bat side of the solenoid, it doesn't have such a wire in the alt harness I used. I know that there is damage in the wiring loom, so I think the best bet is to replace. Questions:
Should the bat terminal go directly to the solenoid?
Since my underdash loom is a non-tach loom I assume I should stick with a non-tach head light harness?
What difference is there between the big block loom and the small block headlight harness except for the tach wiring?
They sell a 67/68 alternator harness w/o tach should I switch to that? Guys, I appreciate the help, I darn near burned up my car after working on it for two years. That would have sucked.
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