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That is the junction for the optional ammeter. The wires will go from the alternator to this, to the gauge on the dashboard. It can be removed/rewired, some feel that an ammeter is dangerous. So is waking up, you pays your money, you takes your chances.
Some people used the bolt to retain the wires in the same orientation and then wrap it with some electrical tape. You don't want that connection to touch the fender which is chassis ground. It's designed to hold the wiring off a ways from making contact.
Went from a standard instrument panel on my 65 to a custom panel that included the oil pressure and alt gauge. Took awhile to hook up the alt gauge I had concerns running a high amperage circuit to my instrument panel. Likely would not be an issue but I decided to go with a fused junction block purchased at local auto parts for less than $10. There are numerous fuse block options but found the 50 amp fuse block as an alternative which I installed numerous years ago.
You can get a junction block on e-bay cheap. Black Junction Block / Power Post Insulated Terminal 3/8" Stud - Stainless Steel | eBay
I'm guessing you have the optional oil and ALT. gauges. That wire going to the gauge is quite heavy and more than capable of handling 70 amps. Problem is the gauge isn't. There is a copper shunt in the gauge that will melt if you get a short. The large trucks used a fuse block to protect that circuit. I added a resettable 70 amp breaker that accomplishes two things, it protects the gauge and gives me a way to shut all the power off to stop the electrical vampires from killing the battery when the truck is sitting.
You can get a junction block on e-bay cheap. Black Junction Block / Power Post Insulated Terminal 3/8" Stud - Stainless Steel | eBay
I'm guessing you have the optional oil and ALT. gauges. That wire going to the gauge is quite heavy and more than capable of handling 70 amps. Problem is the gauge isn't. There is a copper shunt in the gauge that will melt if you get a short. The large trucks used a fuse block to protect that circuit. I added a resettable 70 amp breaker that accomplishes two things, it protects the gauge and gives me a way to shut all the power off to stop the electrical vampires from killing the battery when the truck is sitting.
I like the set up. Your engine bay is very clean!
the night the alt gauge stopped working correctly, I was driving home and my headlights and dash lights were brighter then ever, my alts were reading 60+ and about 10 miles into driving dash went dark, blew all the lights, the only light that stayed working was the alt gauge light and it was really hot to the touch. I ended up replacing battery, alternator and voltage regulator. Alt gauge never worked properly after that.
If you're not going original swapping out the amp meter for a volt meter eliminates the need to run the heavy cables to the dash. Page 4 of my build has some details/pictures.
If you're not going original swapping out the amp meter for a volt meter eliminates the need to run the heavy cables to the dash. Page 4 of my build has some details/pictures.
I got a new junction box, one from eBay. Not an oem one. Plugged the wires in and the amp gauge is acting like an rpm gauge. It moves however the does. Any ideas what to check?
here’s a back story- when I got the truck everything worked as it should. One day driving home, volts were reading through the roof blew out dash lights. I didn’t know what happened so I replaced voltage regulator, alternator and battery. Sense then the volts gauge hasn’t worked correctly and then I noticed the junction box was broken so I thought that is why my volt gauge isn’t working. And now my alternator isn’t charging the battery. After a day of driving it won’t start back up. It’ll act like a dead battery. But if I park and try and to start it up in the morning it’ll start up just fine as if the battery is charged.
Don't throw parts at a wiring problem. Buy a wiring diagram. Go through that 56 year old wiring harness, clean the connectors ,restore the grounds, straighten up whatever mess other people have made. Then replace the parts that failed because of bad wiring.
My 1966 custom cab has 2 amp gauges. One is a light and the other a calibrated gauge. Amp gauges go in line and read current flow; an amp gauge is set within one positive wire (on a positive ground car) to measure current flow. If the gauge fails, it opens the circuit and on many cars the failure will stop the alt from changing because the system has an open.
A volt meter is across a negative and positive pole of an electrical system with 2 wires reading voltage in the system. The other gauges in the truck, like fuel and water temperature gauges are accentually volt meters that measure variable resistance/ voltage from a sender unit to the calibrated gauge face with a case ground to the block on the sender. The ammeter has no ground and should never touch ground or it is a toaster.
I would do what Crop duster suggested and I would add because you have 2 amp gauges undo the one that shorted and see what happens. The amp gauge light in the cab should work because that amp gauge is in a different wire.
Moreover, the oil pressure gauge and oil light on my custom cab 66 truck are volt meters measuring resistance of the voltage to the gauge and displaying on the face or lighting the light when voltage falls to low.
steve
There are a few ways to wire the ALT circuit, perhaps if U can post a drawing member may be able to provide advice?? I am too slow figuring out electrical wiring diagrams and had a heck of a time trying to figure out the ALT circuit, a FTE member PM a diagram and it took an hour to run the ALT circuit, this was many years ago.
