Hi everyone,

I recently acquired an EF Fairmont as a bit of a project, and I have a problem.

volt meter was reading very low on the dash, so I tested the battery with a voltmeter (12.6v) and with the engine running (11.8 and dropping). I figured just replace the alternator and all will be well.

Got a replacement alternator and tried unlocking the car with key fob and no luck. Tested battery voltage - 0.00 - I then thought maybe there is a massive amp drain so charge the battery and try to track it down, but the charger didn't want to know about it so I took out the battery and tested continuity between the positive terminal and the chassis and it was bad news - 0.00 (so earth short?) disconnected a whole lot of wiring and it appears the the wire on the battery fuse and ignition fuse are showing a connection to earth...

Is this going to be a nightmare to fix? New loom time? Or is there something I have done wrong?

Firstly... You never check for continuity on a voltage wire with voltage already on it... Continuity puts out a voltage and then measures the current flow... You shouldn't try to put a voltage onto a voltage wire you'll blow a meter up or damage something else...

Once you had the battery disconnected then a short circuit on the postive lead probably doesn't surprise me... You are measuring the impedance of everything on that wire to earth in parallel which will give a low resistance... Disregarding continuity, what resistance did the meter actually show up (continuity will usually beep for less than 40 odd ohms...)

Lead acid batteries fail open circuit... Is the battery still zero out of the car... You can try ignoring the battery charger and just hook it to another battery with jumper leads... Be very careful, if the battery has failed for some reason it could exploded... I've seen batteries that have been too flat for a smart charger to begin charging, given them a quick boost off another battery and off they go...

I'd whack a new battery in it first, if you get a big spark when you hook on the last terminal chances are you did have a short and it SHOULD blow a fuse on that circuit... At least you'll know where to look then... Needle in a haystack if you do have a short... May be nothing wrong with the alternator... Occasionally a lead acid will get to a point where the alternator is trying to charge it but the voltage wont rise up, appears to be low... The alternator is trying and working fine but the battery is failing and pulling it down... Happens at work all the time and my last car battery did just this... Replaced it and saw the system voltage rise back up that touch to 13-14odd...

Cheers,
Tim

Thanks Tim,

I probably didn't explain very well before - I didn't check for continuity with the battery connected, I had already removed the terminals first. Battery was brand new from the store, I charged it while it was out of the car and it charged fine, is now back to showing plenty of voltage.

I just used a multimeter (doesn't have a beep function) set to 200 kilo-ohms (I think - the 200 setting) connected the negative lead to the chassis, and the positive probe to various different wires on the main fuse box and alternator wiring. A couple of them (such as the wire from the non-battery side of the battery fuse) were showing 0.00 or a direct line to earth. Is that normal? I would have thought that indicated a major fault.

Also, when I had first tried charging the battery (with it still in the car) the charger didn't want to know and just started clicking on and off, yet charged perfectly once the battery was removed from the car

hmmmm... Maybe there is a problem...

Don't set your meter to kohms... You want the most sensitive setting... Is there a 20ohm or 200ohm setting? These circuits might only have a few ohms them, the 200kohm scale probably wont go small enough for you to acurately get a value...

If you get low ohms still I'd be looking for a problem yes... Try first by finding your low resistance battery lead and pulling fuses til you see a major change... Or pull them all and see if it fixes it... If it does then it's past a fuse... If it doesn't you may have a short between the battery and the fuses...

See you'd only need a filament globe to be on (like a door open when the door buttons are connected directly to lamp) or something like that and you will get low resistance because a globe has bugger all until it gets white hot... (As things get hot their resistance goes up)...

Cheers,
Tim

I pulled the fuses and tested the wires, and the readings were better with the ignition fuse and battery fuse removed (also at one point the ALB fuse).

Doors weren't open, but shouldn't have any effect without battery connected?

It's a strange problem I haven't seen before, and I would have expected some blown fuses, but they all seem fine

I'd be sucking it and seeing... Just hook the battery up... Avoid looking down over it incase it sprays up and hoping for the best... It's hard to know... If you see smoke you have a wiring short and probably should pull the lead back off and investigate further...

Cheers,
Tim

Hmmm really not to keen on that approach for the following reasons:

Brand new battery was completely emptied just about overnight
charger went spastic with terminals connected
(both leading me to believe there is a problem)
Even if the problem has gone away, it could be temporary, and I would rather not be driving along the highway and have the electrical system crap itself.

Thanks for the input though, but rather find and repair the problem

Did you disconnect the battery when you changed the alternator?

Haven't got around to putting new alternator in yet, but yes, I removed the battery before disconnected the old alternator

Get the battery checked, you may have dropped a cell.

okay, will take it in to work and put it on the tester, but why does the charger charge the battery nicely out of the car, but then goes spastic if it's in the car? It confuses me, the whole thing seems strange

refit battery - connect negative side - buy a in line fuseholder and a handful of 30 amp fuses - connect fuse holder to battery positive with fuse in and touch against each positive circuit until a fuse blows - you can then at least work out what is working and what circuit has a short across it by connecting other circuits and seeing what works or tracing the faulty circuit - dont ignore battery cable as you may have a faulty starter-possibly locked in mesh and check power cable to the altenator -(alt may be shorted or possibly the cable to it) also possible short in ignition switch etc etc ....

mind you dont burn your fingers and be aware of sparks near a recently charged battery as the gas is explosive - blow fumes away and drop a damp cloth over the battery -protective glasses etc

battery is still a possibility -wouldn't be the first new battery to fail ..................

Well we have progress!

As SWC (and others) suggested, I tested the battery, all seemed okay. I then hunted around the main loom, pulled guards and bumper off and checked it all - there were some dodgy looking, poorly insulated wires, so I fixed all that up and re-insulated everything.

Installed replacement alternator, and put the battery back...... Hooked up the multimeter, and started swearing at the thing! Turns out part of the problem was the multimeter is goosed I had charged the battery the other day and left it sitting for a few days, multimeter said it was sitting at 17 volts....

I tested it with a different meter, and it's now at 12.6 with everything off, and 14 with engine running - success!

Now to reconnect everything, and see if it keeps working...

and DON'T believe a new battery won't fail .... been there done that

I know, I sell them This one seems okay though, went on the tester and passed with flying colours