Help! Suspecting a mystery short!

[porsche0nut]

1986 Carrera.

Early December after the car sat for about a month, I tried starting it. Car wouldnt start. Battery was drained. I tried boosting it, no luck, so I left it for winter and took the batter out and put it on a tender.

So this past Tuesday, battery reads good, so I put the battery in the car, it starts up and I go for a drive. Awesome.

Get to the car today. Turn the key and nothing happens. Battery is drained down to 7v.

I try boosting it. No luck, tries but doesn't turn over. I noticed the booster cables are pretty hot.

Thoughts??

[Ronnie's.930]

First take the battery to an auto parts store and have them load test it. After you determine that the battery is good, or you buy a new one if it isn't, start the car and measure the charging voltage at the battery terminals (should be above 13-14 volts - plus or minus a couple of tenths) at 2000 rpm.

[porsche0nut]

If it was the battery, why am I unable to boost?

My battery is a 1yr old optima red top... Can they test this just like a regular battery?

Thanks

[porsche0nut]

I checked continuity with my multi meter.... It tells me continuity between the positive and negative leads of the battery... Which is why I suspect a short somewhere.

[porsche0nut]

I have now disconnected the starter... Still continuity, which tells me the problem is before the starter in the wiring.

I then pulled every fuse, checking the continuity between battery leads in between and got nowhere. I have no fuses left and still reading continuity!!

I'm lost.

[tirwin]

Jonathan,

Looked at the wiring diagram for my SC (don't have an '86). There are 2 things to look at: the path from the battery to the CDI and to the ignition switch. Has to be something like that.

[porsche0nut]

Thanks Tim... we've dug into the fuse panel a bit... we realized that from the positive terminal of the battery there are 3 separate leads (4 wires, one lead has 2 wires from it) and that testing continuity from them all as they are joined wasn't helping isolate the issue.

Good news was that 2 of the leads (3 wires) were good, no short. The 3rd lead we isolated as the "problem wire". It goes to the fuse panel.

So now we start pulling wires out of the top of the fuse contacts... some are good, some are bad. It's a very complicated mess of wiring, with fuses jumped together and some fuses grouped off the same bus... difficult to isolate things. In the end, we have about 5 wires that we have deemed "problem wires" that feed the top of the panel... from those 5 wires a few more fuses are fed through jumpers or being bused together.

Not sure where to go from here. I really don't want to start tracing individual wires!

[porsche0nut]

Originally Posted by Ronnie's.930

First take the battery to an auto parts store and have them load test it. After you determine that the battery is good, or you buy a new one if it isn't, start the car and measure the charging voltage at the battery terminals (should be above 13-14 volts - plus or minus a couple of tenths) at 2000 rpm.

Well, lesson learned! Start with the simple tests/solutions before over-complicating things! Turns out it was the battery, replaced the optima with a warranty-replacement and all is well!

The good news is that in the process of digging into the fuse box I realized some fuses were incorrect values.

Thanks for the replies guys, I was pretty anxious the other night!

[Ronnie's.930]

Originally Posted by porsche0nut

Well, lesson learned! Start with the simple tests/solutions before over-complicating things! Turns out it was the battery, replaced the optima with a warranty-replacement and all is well!

I'm glad that worked out for you before you went about replacing all of the wiring in the charging and starting circuits!

I've been there before (most here probably have at one time or another) - I own a 1990 e350 diesel that experienced a sudden "no crank" situation . . . both batteries were less than a year old and measured at 12.6 resting volts (so couldn't be that, right?) . . . took the starter off and had it tested (good), replaced the starter solenoid (no change), replaced the glow plug controller (no change), finialy took the batteries in for load testing and one of them had 5 dead cells - duuuuuuuuuuuuuuuu - definitely learned a lesson there!