Battery Draining

Several years ago I installed a Centech wiring harness to my '69 after a near electrical fire when the stock key switch got stuck in the start mode.

Since then I noticed that my lights would change their brightness based on the RPM of the engine, which I was led to believe that my alternator was going bad or not powerful enough. I replaced my stock alternator with a 135A alternator that I had bought several years before and never had the time to install it. A couple of years ago the stock alternator finally died about 90 miles from the nearest city in Arizona, of course %), so now was my chance to install the new one.

After installing the new one, it worked for a few months then stopped charging (again at the same place in Arizona - probably won't be going back there again ;D). It had a built-in regulator and I was able to find a kit that I could rebuild it with and tried that a couple of times with no luck. I finally decided to go back to a stock alternator. I fired it up after the install and thought everything was good, but the next weekend I went to start it and the battery was dead

I bought a new battery and a few days after installing it, it was dead. So I obviously have a short somewhere.

I bought a Power Probe III to try to help track it down, but I'm not really sure where to start. I read in a post this morning that using a multi-meter you can pull one of the cables off the battery and connect one probe to to terminal and connect the other end to the fuse holder and figure out which circuit is bad.

I disconnected the negative cable from the battery (mostly to keep it from draining) and connected the Power Probe's black connector to the negative terminal and the red to the positive. I then went to the fuse block and pulled each fuse to see what would happen. On all but a few of the fuses one side was hot and the other was not. But, on the Heater, Backup/Inst, Alt/EMM and IGN SYS fuses, both sides were hot.

I'm not sure if those circuits should be hot on both sides or not or if one of them is my problem.

Any advice on how to track down my short and if anyone has experience with the Power Probe in tracking down a short, I would appreciate any advice. It's been over a year since I've been able to drive my Bronco and this is the perfect weekend to get it out and drive

Thanks!

Well to start with just do a simple check to see if you have a draw. Take the key out of ign. Open the hood and pull the POS battery wire. Keep NEG wire hooked up. Take a 5 dollar 12v test light and attach the clip to the POS terminal. Take the pointed end and touch it to the POS wire you disconnected earlyer. If the light comes on bright you have a large draw. If the light comes on dim you have a small draw. if the light dont come on at all you have no draw.

Hopefully the light dont come on. If you have a radio the wire that keeps the memery for the presets and clock will always draw a small amount of power. There is a larger power wire that only gets power when key is turned, but there is a second smaller wire that always draws power (memery wire). Its best to desconnect that memery wire so you dont get a false reading.

Start there and get back to us.

Also pull that alternator and have it checked at your local auto store. Make sure the alternator checks out good. Id take that battery back in and have it checked also. Draining a battery "dead" destroys it in a hurry unless its a deep cycle.

If you do find a draw (after you varifyed the radio is completly unhooked), then start pulling the fuses until the light goes off. That Gives you a idea what circut the draw is on. On the factory harness things such as the horn are not fused. My horn was grounding and i found it by following the smoke!

bknbronco said:

Well to start with just do a simple check to see if you have a draw. Take the key out of ign. Open the hood and pull the POS battery wire. Keep NEG wire hooked up. Take a 5 dollar 12v test light and attach the clip to the POS terminal.

Click to expand...

Tried that with a voltmeter and it was pulling 10.7 V (all that the battery is currently putting out). I pulled each fuse and it was consistently 10.7V.

A friend of my son's suggested testing the alternator wires and with the key off, both the field and alternator wires were at 10.7V (with the cables back on the battery).

Next I'll try pulling the alternator and have it tested. It's a reman and I've had bad luck with them in the past.

Any other info is greatly appreciated. My Bronco has been down too long with this problem. I might have to resort to taking it in for someone to fix it, which I really don't want to do!

Do you still have the external voltage regulator? is it the newer style? The new ones are fancyer and short circuit protected.

bknbronco said:

Do you still have the external voltage regulator? is it the newer style?

Click to expand...

I suspect the voltage regulator as well

I do still have the external voltage regulator and it's fairly new (bought not too long before installing the internal regulated alternator) but I have no idea if it's the "newer" style.

Edit:
I read through a different post and figured out the difference, mechanical is old, solid state is new. Just ordered at Napa and will pick it up when I go into town today.

Finally!

It was the voltage regulator! ;D

The Field to the alternator is reading zero with the key off and there isn't anymore drain when I have the positive disconnected and a multi-meter between it and the positive terminal.

Who knew that a $15 part could keep me from driving my Bronco for the past 18 months!

Thank you bknbronco and Nobody for getting me to look at that!

ATTA BOY! Now drive that damn bronco and keep them electrical gremlins out!!