89 Winnebago, alternator causing short?

[fire-99]

We have an '89 Winnebago Chieftain which as been sitting for awhile and has developed a distressing issue.

When I try to hook up the battery I get a massive arc and the fusible link for the main power from the starter has burned up.  I've traced this to the alternator but I think there's more to it than that. 

I trace the wire up to a solenoid in the engine compartment where the wire to the alternator joins up.  I discovered that if I unhooked the alternator then the short would go away. 

I took the alternator out and had it tested at the local NAPA, it showed bad so I bought a new one.  I put the new alternator in but get the same problem with arcing when I try to hook up the battery.

I know there's something more involved but there are way more wires in this thing than I'm used to. 

Does anyone have any suggestions? 

 

[afchap]

I had a similar problem years ago on a Ford van ...melted the voltage regulator and burned up several other electrical components, and blew the end off my favorite pair of pliers before I found I had a direct short on the ground cable from the battery. It was between a header and the car body and the insulation had burned off. I would suspect you have something like that going on somewhere. I would try to physically trace all the heavier electrical cables, both positive and ground starting with battery, alternator, and starter connections.

 

[seilerbird]

Are you absolutely and positively sure you are not hooking the battery up backwards? That will cause an arc.

 

[Lou Schneider]

Get a 12 volt light bulb and socket and connect it between one of the battery terminals and it's cable, so that all the current flows through the light.  This will limit the short circuit current to a safe value so you can troubleshoot the problem without burning anything up.

As long as there's a short, the bulb will glow at full brightness.  When you eliminate the short the light will go out.

If your alternator uses an external regulator, the regulator could be bad even if the alternator itself tests good.

The solenoid sounds like the one that connects the house batteries to the alternator for charging.  There's not any possibility the house batteries are completely dead, shorted or connected backwards, is there?

 

[Art In Mobile]

You are getting some great advice here! I would not expect anything less! I will also second the reverse polarity of the battery idea as a possible problem. A reverse battery will blow the fuse link in an instant. So would a short to ground. If that is not it, the lightbulb in the curicut to check it out for shorts is an EXCELLENT idea.  (where did I leave that spell check again) Art

 

[fire-99]

Are you absolutely and positively sure you are not hooking the battery up backwards? That will cause an arc.

Almost positive, I'll feel quite stupid if that's the case but I'll check to be sure.

 

[fire-99]

Get a 12 volt light bulb and socket and connect it between one of the battery terminals and it's cable, so that all the current flows through the light.  This will limit the short circuit current to a safe value so you can troubleshoot the problem without burning anything up.

As long as there's a short, the bulb will glow at full brightness.  When you eliminate the short the light will go out.

Is there a way to bypass this solenoid and take the house batteries out of the equation?  Is it as simple as just unhooking the wires from the one side of the solenoid and joining them together?

If your alternator uses an external regulator, the regulator could be bad even if the alternator itself tests good.

The solenoid sounds like the one that connects the house batteries to the alternator for charging.  There's not any possibility the house batteries are completely dead, shorted or connected backwards, is there?

Good advice.

I'm positive that the house batteries are surely completely dead, so do I need to try throwing a charge into them?

The alternator is an internal regulator deal.

 

[Lou Schneider]

The solenoid is a switch - when it's energized it connects the two large posts together.  One side should come from the house batteries, the other from the starting battery and alternator.  So yes, getting it out of the circuit is as simple as removing the wires that are tied to one post (the wires from the alternator and the starting battery) and tying them together.

Or leave them on the solenoid and remove the single wire (going to the house batteries) from the other side.

I mentioned the house batteries in case the solenoid was defective and was permanently connecting the two together.

If the house batteries are completely dead, and have been that way for a while, they're probably toast and should be replaced after you get everything else working.  You can try charging them, but I doubt they'll take much of a charge.

 

[Mavarick]

I agree, I would remove and bench test all the batteries to make sure they will take a charge etc and are not shorted then check for bad wiring from there.
One other piece of advise before you start unhooking everything. Take pictures of all the wiring before you remove batteries etc so you have a record of where you started. It helps to trace things out and use colored electrical tape, if necessary, to mark wires.

 

[fire-99]

I agree, I would remove and bench test all the batteries to make sure they will take a charge etc and are not shorted then check for bad wiring from there.
One other piece of advise before you start unhooking everything. Take pictures of all the wiring before you remove batteries etc so you have a record of where you started. It helps to trace things out and use colored electrical tape, if necessary, to mark wires.

I learned this part the hard way recently when taking a motorcycle apart to do a bit of work to it.  I swear when I was younger my memory was better but now if it doesn't go back together the same day I might as well forget it.

I'm going to hit this again pretty hard this weekend and see if I can't get something figured out.  I'll post back then but in the meantime I'm still open for suggestions.  Hopefully it gets a little cooler before I have to go back out.

 

[fire-99]

Are you absolutely and positively sure you are not hooking the battery up backwards? That will cause an arc.

Well darn it all anyway.  Can you believe this was the problem all along?

Side post battery that I didn't look at before I put it in, I just hooked it up the way the cables fell naturally.  Well this Winnie has been unnatural since I've been working on it so I don't know why this would be any different.  I was able to look through the grille and see the polarity and I had it wrong.

Once I changed the cables everything works perfectly.

Thanks to everyone for all the help!

 

[John Canfield]

Tom wins the monthly troubleshooting prize!  Now we need to figure out what the prize is  .