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Short Circuit or bad alternator? '87 B250

12-22-2007, 01:49 AM
My van has been eating batteries lately. Its my band van so I don't drive it a lot - about once a week to and from shows in town.

The last 3 or 4 shows we've had I've either had to have it jumped to get to the show or have it jumped after the show. When I get it jumped and then leave it running for a while it'll start up by itself but then when I leave it sitting for even a day the battery will go dead again.

I've taken the van to the local Schucks and Autozone and had them hook up their tester to the battery to check the alternator and battery and the tests always come back ok. However, on more than one occasion I've taken the battery out and had them test it in the store and they tell me its bad so I don't really trust their tests.

I also purchased a little handheld battery/alternator tester but I'm not sure I trust its results either as they always seem to show something different.

So my questions are: Does this sound like a bad alternator or a short circuit somewhere? Are there any test I can do to find out which one is the problem? If it is a short what would be the best way to go about finding it?


12-22-2007, 02:03 AM
Right now your battery is shot and needs to be replaced. But to prevent this from happening again, read on:

The lifespan of lead cell batteries like in your van are dramatically reduced when they are drained and recharged often. If a battery is kept "full" like when a vehicle is driven daily (or close to) then it generally lasts it's full lifespan. In your case where the van is being used once a week, the battery is being drained slowly, yet constantly, by the on-board electronics. This deep discharge/recharge cycling is what's killing it.

To overcome the problem use a solar powered trickle charger like show at the link below. This will keep the battery fully charged and should eliminate this problem you're having. If your lighter socket works with the key off, this will just plug in there and do it's job. But if your lighter doesn't have power when the key is off, you'll have to connect it directly to the battery with the clips that come with it.

12-22-2007, 02:10 AM
So you're saying that my last battery didn't even make it two months because it was only being driven once a week? That seems a little extreme. This is an '87 we're talking here... there are almost no on-board electronics.

Plus, I live in Portland, OR so a solar charger isn't going to do me the least bit of good this time of year.

12-22-2007, 02:29 AM
Even in an 87, the electronic spark advance computer, a radio, and a dash clock (if equipped) will all draw power even when the key is off. The fact that you're in the middle of winter and it's cold out, compounds the problem.

12-22-2007, 03:24 AM
So what would you say is the longest I can let it sit without running?

Also, I saw these terminal cables somewhere that are for boats and RVs that let you turn a knob on the cable and "disconnect" the cable from the battery. That would keep the battery from draining right?

12-22-2007, 11:25 AM
I have a Mustang GT 5.0 convertible that only gets driven in the summer. When it's off the road in the winter I start it and let it warm up no longer than once every three days. I have a large capacity battery in it and could actually go several weeks and it will start. But that's only because the battery is in good shape and is an extra capacity one. I run the engine every three days not only for the sake of the battery, but for the engine and tranny as well. Sitting too long allows the oils and fluids to flow off of the internal metals and will lead to premature wear.

Yes you can use a battery cut-off switch. But you will lose memory to things like your radio.

Here's one:

12-22-2007, 02:43 PM
Well I just went to the auto supply store and picked up a little circuit tester light. I unhooked the negative battery cable and ran the light betwee the battery and the cable. The light came on. I read that this meant that something was drawing power from the battery. So I went through all the fuses and found that if I removed the #7 fuse that the light went off. Everything seems to work without the #7 fuse except for the glove compartment light. So hopefully that's all it was.

Anybody know what the #7 fuses does? So far the only thing I can see it affecting is the glove compartment light.

12-22-2007, 06:25 PM
I just discovered that the brake lights don't work with the #7 fuse removed. I've checked everything else (reverse lights, hazards, turn signals, headlights, tail lights, interior lights, cigarette lighter, radio, heater/ac, windshield wipers and power windows). So the only things affected are the brake lights and the glove compartment light. Weird.

Any ideas on why the brake lights or glove compartment light would be drawing power from the battery?


12-23-2007, 07:41 AM
The glove box light will only draw power if the light is staying on even with the GB door closed. Removing the bulb and retesting for any draw on the circuit would answer that question.

Brake lights, 4-ways, and turn signals are supposed to be powered from the same circuit. Removing the fuse should prevent all of them from working. Since only the brake lights have stopped this means the wiring has been altered from the factory wiring and as a result factory wiring diagrams will be of no help.

If this van of yours was ever setup to tow, there could be an electric brake controller installed somewhere. This would explain why the brake lights are being fed off of a different circuit. If the live feed going to the brake controller is tapped off of the #7 fuse, this could explain the draw on that circuit.

12-23-2007, 12:45 PM
Yes, this van has a tow harness.

Are you saying that an electric brake controller SHOULD be drawing power?

12-23-2007, 01:18 PM
An electric brake controller is connected to an always live circuit and does draw power all of the time. How much that draw is will depend on the unit itself, make, model, power requirements, etc. Of course they can go bad just like any other component and start drawing more than they should.

Do you have a brake controller for electric trailer brakes in your van?

12-23-2007, 03:35 PM
I'm not sure what one looks like. Where would be a logical place to look for it?

12-24-2007, 02:23 PM
Sorry for the delay in getting back to you. A 24 hour bug hit me like a ton of bricks yesterday afternoon. :(

The brake controller cases are something like 4"x4"x2" and a lot of times you'll find them under the dash for the simple reason of being able to access the wires that have to be tied into. But in reality, if one exists it can be anywhere that the installer felt comfortable installing it.

12-24-2007, 03:03 PM
Is a brake controller required for a tow setup? I don't see anything like that anywhere.

12-24-2007, 05:02 PM
It's not required until the trailer exceeds a specified weight. So to answer your question, no, in most cases for people like us it's not required. It was just a thought to explain the brake light circuit draw.

12-28-2007, 08:37 PM
I think you have a drain on the battery which is excessive. Disconnect the battery ground use a DVOM set to amps and check the draw between the ground clamp and battery negative. You might to disconnect a fuse at a time to find the problem. The tail lights have a switch by the brake pedal poor adjustment or a bad switch will cause problems. The trailer brake unit can be disconnected. Let the vehicle set over night and check if this helps.

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