[EOD Guy]

Friends 99 Mustang, V6, let it sit for more than 2 days battery goes flat, start it every day, it's fine. Alt putting 14.3 across the battery terminals. Multimeter between the pos post and the pos cable, pulled fuses only 0.01 increase in voltage, pulled the Maxi fuses and relays, no changes in voltage. New battery and it's checks out good. Cruise control does not work.

Stumped

[pepi]

With the meter are you measuring volts or amps when pulling the fuses. You should be using the AMP scale for troubleshooting.

[EOD Guy]

I measured volts

[LATECH]

pep is right. check the current draw. Anything over 40 milliamps is to much.
should be a round 30 milliamps or so on the pony. lincolns and cads and such with a lot more electronics can pull 40-50 milliamps as a norm.
.0050 = 50 milliamps or 50/1000 of an amp.
.0030 = 30 milliamps or 30/1000 of an amp.
This is reffered to as a parasitic draw. some is allowable to maintain memory circuits in the radio the pcm and other devices.

[Don Lyon]

With key off, underhood light bulb removed(if so equipped) dis-connect POSITIVE batt. cable. Connect test light BETWEEN battery and CABLE. Light should be out. Remove one fuse at a time, when the test light is on, thats the circiut causing the grief. Just did this on a 96 Chevy truck, it was the Radio / Batt fuse circuit. (Of course it was the last fuse pulled)

[EOD Guy]

I'll give it a try

[LATECH]

Hook the light between the negative cable and the negative post. Make sure the dome light is disabled as the door will be open. When you start pulling fuses the light will be ON, when you pull the fuses on the affected circuit the light will go OFF. Just to clarify things a little. If it is a low current draw the bulb may not glow very bright, it may actually just look a little red,if you dont see a light look real close.It may just be barely glowing, depends on the bulb and the size of the draw .

[LATECH]

Originally Posted by Don Lyon

With key off, underhood light bulb removed(if so equipped) dis-connect POSITIVE batt. cable. Connect test light BETWEEN battery and CABLE. Light should be out. Remove one fuse at a time, when the test light is on, thats the circiut causing the grief. Just did this on a 96 Chevy truck, it was the Radio / Batt fuse circuit. (Of course it was the last fuse pulled)

Don had the right idea just wrote it down wrong, not meaning to nit pick...just saw it as a little confusing thats all. Good luck.

[EOD Guy]

I got the jist of what he was saying..... what's the difference between the pos side vs the neg side of the battery?

[LATECH]

Disconnecting the positive side means the tool you are using is charged psoitive and can short out if it touches metal
Not a good thing.
Also I have seen where it can also cause a voltage spike that will take out some of the electronics. I have seen car alarms killed that way, allways disconnect the neg first, and re connect it last. Period.

[Don Lyon]

All I know is the method I used worked for me and was recommended by several others, but next time I'll try the oposite method. It's a poor day when you don't learn something new.

[pepi]

Originally Posted by latech

Disconnecting the positive side means the tool you are using is charged psoitive and can short out if it touches metal
Not a good thing.
.

latech is right, if you bump something with the wrench disconnecting or tightening up the POS post/cable ............. ZAP!

Reason you are completing the path to ground and have a dead short, it's the same as if you just put the wrench across both posts of the battery.

Could hypothetically explode the battery, there is a load of amperage going through the wrench, the whole batteries worth. What 80 -100 amps at least?

POS first and then ground, no sparks ever, much safer. Disconnecting the battery NEG/ground first isolates the battery. Battery jumper cables should also be hooked up POS then NEG.

[EOD Guy]

Ok, so I'm getting there isn't really much diff between the actual test (pulling the fuses) using the neg or pos terminal......... I'm well aware of the wrench shorting between pos terminal and the body etc.... I also wouldn't lay the wrench on top of the battery so that it would short across the posts/cables etc.....

[LATECH]

Originally Posted by latech

Hook the light between the negative cable and the negative post. Make sure the dome light is disabled as the door will be open. When you start pulling fuses the light will be ON, when you pull the fuses on the affected circuit the light will go OFF. Just to clarify things a little. If it is a low current draw the bulb may not glow very bright, it may actually just look a little red,if you dont see a light look real close.It may just be barely glowing, depends on the bulb and the size of the draw .

Read it again if you didnt see it the first time. The way don stated it was backwards, at least the way I read it.
Once again disconnecting the positive first can throw a voltage wave Or spike through the system due to capacitive discharge in some circuits. All that power looking for a place to go can kill some electronics in a search for a place to dissipate, you know capacitive discharge is a type of ignition (hi Voltage) just a saftey precaution for your electronic components.Plus as was said before you dont want to short out the wrench in your hand, but I see you got that.

[LATECH]

Originally Posted by Don Lyon

With key off, underhood light bulb removed(if so equipped) dis-connect POSITIVE batt. cable. Connect test light BETWEEN battery and CABLE. Light should be out. Remove one fuse at a time, when the test light is on, thats the circiut causing the grief. Just did this on a 96 Chevy truck, it was the Radio / Batt fuse circuit. (Of course it was the last fuse pulled)

Just trying to keep the facts straight so you get the test down right, like I said he had it right just had the light status backwards thats all, just thought it may confuse you.