Ammeter Wiring

[Kilgon]

Hi,

Trying to find out if anyone knows exactly where the wire splices are for a 71 Fastback ammeter.  My oil and temp work on my center gauges but the amp does not.  I have tested the gauge and it is good.  I also tried a spare I have. 

 I have checked the wiring diagram but am unable to determine where number 654 and 655 splice are at.  I have trace 654 and it is tied into 37 right after it comes out the fuse block connector. I don't know if this was done at the factory or not. I have traced 655 into the block connector but the wire is missing on the out side to the firewall.  

The socket is empty where it should be at.  I plan on running a new wire but am not sure exactly where to tie in at what point.    Below is where 654 ties into 37 out of the back of the fuse block junction.  The upper left hand corner is where 655 should be but it is missing.

Any help or ideas would be appreciated.

 

[midlife]

Well, that splice is incorrect, for one. You have a standard (non-ammeter) headlight harness, so you don't have the proper signals feeding into the ammeter. The feeds for the ammeter start near the starter solenoid (one side) and the other where the alternator feed joins the main power feed, a few feet away from the starter solenoid, buried in the headlight harness.

 

[delawarebill]

ha midlife. i'm always amazed at the knowledge many of the folks here have... nice job..

 

[Kilgon]

Well, that splice is incorrect, for one.  You have a standard (non-ammeter) headlight harness, so you don't have the proper signals feeding into the ammeter.  The feeds for the ammeter start near the starter solenoid (one side) and the other where the alternator feed joins the main power feed, a few feet away from the starter solenoid, buried in the headlight harness.

I sorta figured that splice wasn't right.  If I rewire the harness to the correct wires should the rest of the electrical system be ok? I know that the voltage regulator is wire different then it is if you have a amp light.   Would you happen to have any pictures of where the splices are?  

Thanks  for your help.

 

[Don C]

The ammeter is a shunted ammeter and functions from only a sampling of the amperage the car is using or the alternator is providing, not the entire load. The shunt is in the correct wiring harness and not a matter of connecting wires. You either have to have the correct wire harness or a lot of electrical knowledge to make your own shunt. If you want your ammeter to work get the correct harness from Midlife.

 

[Kilgon]

The ammeter is a shunted ammeter and functions from only a sampling of the amperage the car is using or the alternator is providing, not the entire load. The shunt is in the correct wiring harness and not a matter of connecting wires. You either have to have the correct wire harness or a lot of electrical knowledge to make your own shunt. If you want your ammeter to work get the correct harness from Midlife.

 

[Kilgon]

Thanks for the info Don. I'll get with Midlife. I visited his site but it seems they recommend to get a new harness instead of a having mine refurbished.

 

[Don C]

Refurbishing your harness will not add the shunt or other connections, a different harness is required.

 

[SteveO_71]

Do you really want to use the ammeter, especially since they never seemed to work even when wired correctly? Then add to that, the fact your harness is not correct.

May want to do the RCCI ammeter to voltmeter conversion. At least, thats straightforward +12 and gnd wiring.

https://www.rccinnovations.com/index.php?show=menu-volt-all

M7123V - Volt Meter for 1971-1973 Ford Mustangs

The M7123V is the Amp meter from a 71, 72 or 73 Mustang converted to read volts. It uses the original amp scale, but has been modified to indicate charge/discharge by voltage.

If you prefer a volt meter face, order the M7123VO below.

Notes:

• Unless you specify another configuration, the normal readings (using gas gauge descriptors) for this gauge are:
  D = 9.5V
  ¼ = 11.5V
  ½ = 13V
  ¾ = 14.5V
  C = 16.5V
  

 

[TheRktmn]

Do you really want to use the ammeter, especially since they never seemed to work even when wired correctly? Then add to that, the fact your harness is not correct.

May want to do the RCCI ammeter to voltmeter conversion. At least, thats straightforward +12 and gnd wiring.

https://www.rccinnovations.com/index.php?show=menu-volt-all

M7123V - Volt Meter for 1971-1973 Ford Mustangs

The M7123V is the Amp meter from a 71, 72 or 73 Mustang converted to read volts. It uses the original amp scale, but has been modified to indicate charge/discharge by voltage.

If you prefer a volt meter face, order the M7123VO below.

Notes:

• Unless you specify another configuration, the normal readings (using gas gauge descriptors) for this gauge are:
  D = 9.5V
  ¼ = 11.5V
  ½ = 13V
  ¾ = 14.5V
  C = 16.5V
  

Thanks for the plug, Steve-O

The volts face for the 71-73 ammeter conversion is now available as well:



M7123VO

 

[Kilgon]

I want to keep what I have left of the original for the time being. I have spare gauges so I rather get the right harness. As Don suggested I got with Midlife and am getting the correct harness.

Thanks everyone for the info and help.

 

[midlife]

My website states that headlight harnesses are not warrantied and indeed, they are not. However, in 11 years of doing this stuff, I think I've run across only 3 that were so bad (brittle insulation) that I had to give up. For the 7123's, there are no reproductions and thus no alternative to refurbishment (with the single exception of the 71 non-tach Mach 1 variant, which runs $400. Compare to my $100 refurbishment cost...)

 

[jpaz]

Surprised no one mentioned the fact that the ammeter is also a fire hazard. The wires are always hot, not keyed. So if they happened to groundout then it can start on fire. Volt meter is safe and it gives you a way better idea of what is going on with your electrical system.

 

[Omie01]

Thats why I just opted to put a VDO set in my car. I just never liked the quality of the original gauges, I tried really hard to keep most things on my car as original as possible, but the small gauges had to go!! I have never regretted it!!

 

[Kilgon]

I'm starting to have seconds thoughts about it. Replacing the gauges may be the best way to go. I'm afraid I might open up a can of worms replacing the harness. I know I can get the ammeter converted to a volt meter but I still have the older gauges that are at risk of failing. What are a few of the midrange cost meter brands out there?