For some time I have been upgrading my 1982 E350-based Motorhome with the 460 engine and C6 transmission with GearVendors Overdrive. Recently, I encountered considerable battery drain with ignition and all accessories off. It turned out to be a bad diode or diodes in my alternator. I decided to replace the existing unit with 140-amp hybrid Ford/GM one-wire alternator. As usual, I searched this site for comments, opinions and problems. My motorhome dash instrument panel sports an ammeter (which seldom moved a measurable amount charge or discharge). I want a functional ammeter!

I quickly encountered a series of dire posts about the unsuitability of the shunt ammeter, as installed, in conjunction with high output alternators. The original unit was rated at 70A and I'm essentially running it up a factor of 2 in output current. There were warnings of fires or other thermal damage to the wiring harness. Finally, I wanted a useful ammeter, not one that could read + or - 140 amps full scale. I wanted a full scale ammeter of + or - 50A.

In searching this site, 460Ford and several Mustang sites, I found that several individuals had measured the resistance of the shunt at 0.002 ohms and full scale deflection of the stock ammeter was around 125 millivolts. With some experimentation and a bit of internet research, I found that 5 feet of stranded 6 AWG wire corresponded to 0.00226 ohms and that a 10 foot length of that same 6 AWG wire could carry 140A without the surface of the insulation exceeding 105 degrees Fahrenheit in open air. As a result, I concluded that by replacing the stock wire from the starter relay junction to the alternator output with 5 feet of 6 AWG wire, I could have a shunt and robust current carrier for a sensitive ammeter which would not be damaged by intermittent currents above 100A.

To implement the modification, I located the input lines to the ammeter, connected the battery side input to the starter relay junction post and the other side to the Alternator output terminal. I connected the alternator output to the starter relay junction lug with a 60 inch long 6AWG cable with soldered connectors on each end. Of course, with the 1-wire alternator, I removed the wiring for the voltage regulator and cut the end connector off of the stock power lead to the alternator. In so doing, I am using the 6AWG wire as the ammeter shunt and the current carrying lead to the battery. I have also left the multiple fuse links that tee off the main link at the starter relay junction lug intact.

For the results: After discharging the main battery to 12.3 V indicated, I started the engine and saw a surge current of 110 amps which quickly dropped to 50A then 37.5A and finally to a charging rate of 5.8 amps. The in dash ammeter read full scale at 50A. At the ammeter needle indicating the first tick on the charging side (halfway to full scale) my calibrating ammeter read between 25A and 27A! More than accurate enough for my taste. With headlights and all blowers running, the ammeter registered just beyond the midpoint tick on the discharge side.

Hope this helps someone else pondering the 1-wire or 3G alternator upgrade!

 

Nice!

 

Yes, great repair

One of the problems always had is with the OEM wiring, they use a high content of copper which in time *and '82 is a lot of time* corrodes inside the jacket (insulation) You'll notice this when cutting back the jacket, and seeing the once bright copper wire turned black.

Replacing the wire as you did, resolved what might have been a interior corroded wire.

 

Definitely true, always observed at the connector end when cutoff and renewed. I usually have to strip back an inch or more if I reuse an OEM wire.