Trouble with hooking up battery and solenoid

[69F110]

Everything was disconnected and some wiring removed. I put new cables on and rewired everything to the best of my ability, which is sketchy at best.

Once it was all rewired, I connected the negative terminal and when I put the positive terminal on it arc’d huge- left a dent in the terminal lead and the battery post.

I read online the positive should be attached first, so I hooked it up positive first and when I connected the negative cable, it arc just like the other...

So, I disconnected it all and left it sitting. The diagram I attached is what I used as a guide. I will walk through everything again in the morning.

Any ideas why it would arc like that? No switches are turned on, the ignition switch was off as well.

Thanks for any suggestions.

[HOWDY69]

I was hoping someone more knowledgeable would respond but I will help to the extent I can.

I think we can say that something was switched on or there is a closed circuit that isn't supposed to be closed. Obvious things that could have been on would be the headlights, radio, dome light, instrument lights. Of those it seems to me only the head lights would have sparked as you described.

If the solenoid or something in the ignition circuit was closed the starter would have moved so I don't think the problem is in that circuit. But the starter does draw a lot of power.

This is a wild idea but charging the coil would pull some current but I'm not sure what wires would have to be connected to charge the coil when you connected the battery.

All I can suggest is to make sure everything is switched off and then inspect the wiring looking for a wire that closes a circuit or is in parallel with a switch, which would be the same as being switched on.

You haven't made any unauthorized offerings have you? If it was the arc of the covenant you're in big trouble (ref Lev 10).

[HOWDY69]

I asked your question over on Reddit. Here is a link.

https://www.reddit.com/r/MechanicAdvice ... ecting_the

My son and I are getting close to putting the battery back in his 1971 Mustang so I need to know this stuff.

[pcmdub]

Steve,

To get an arc that leaves a dent, you have a short somewhere. However, if you left it connected, then your battery should be dead in about 1 hour. If you unhooked it (smarter idea), then you need to find the short.

Finding a short: Grab a multimeter and set it to continuity. With the battery unhooked, find the resistance between the + and - cables. If this is Zero or close to it, then you have a major short. If this varies/fluxuates then you have a bad circuit/gauge/switch that is grounding out. To fin the culprit, just start unplugging extra items until it stops or the resistance goes up.

Guesses: Ammeters are problematic because they are basically shorted leads to find the "differential" of current. Ignition switch on the diagram looks odd, you will have to take a picture of the actual wiring to see if it is incorrectly wired. Voltage regulator could be bad too, but not sure until you test it separately.

[two-bit]

Is it possible that the charge wire from the Alt to the solenoid. Is mounted to the wrong stud on the Alt. ? That would cause a direct short to ground and make a pretty good arc hooking up the battery cables. Just a guess.
Two-bit

[MadMike]

There are slight differences in the years and if the truck uses gauges or idiot lights.
Wire it up as though it has lamps rather than gagues, or vice/versa, and the circuits will not work correctly.

More detail on what year, what gauges, and how original the harness is will help. There are slight differences and will determine how the alt/reg are wired up.