wagontrash

2002 Grand Cherokee Laredo 4.0L that I purchased recentlty. Had a bad alternator (voltage surges while engine running), so I replaced that and verifed battery will hold a good 12+ volt charge when disconnected. Once reconnected....dead in a day/won't start/yadayada. Did the amp draw check and yup..... 0.5 to 0.9 mA when everything is off/sleeping. Then went and tested voltage accross all fuses with a fully charged battery. Fuse 17 (Cluster/Diagnostic Connector) is drawing 0.3 volts constantly, and fuse 29 (rear wiper/washer) is drawing 0.9 volts constantly. I pulled the two 10amp fuses, and let the car sit for a day. Batter is holding a chare reading 12.1 volts. Assuming that the rear wiper/washer circut issue is a bad wiper motor, I can let that issue "sit" for a while, just leave the fuse out and not use it (which I hardly ever do/did on my '96 ZJ) but that fuse 17 draw.... Help Please!

dave1123

I just checked the FSM for my 2000 WJ and the only things on fuse 17 are the diagnostic link and the instrument cluster. IDK what in the cluster needs to be powered up constantly, but I'm assuming that's where the problem is. The cluster is easy enough to remove so try that. Just pry off the plastic shelf bezel in front of it and take out the 4 phillips screws, then pull it out. Disconnect the plugs on the back. You could check the diagnostic link to see if it's got crap in it or frayed wires.

I'm told the odometer mileage is stored in the BCM so that's not stored in the cluster either.

wagontrash

I will give removing the cluster a shot. If that doesn't get me anywhere, maybe I'll try adding a new ground run from the diag connector to the frame.

wagontrash

Hard to say "for sure" at this point...however... I pulled the dash, blew contact-cleaner on both connections, also up into the diagnostics connector. Then cleaned (contact cleaner, and wire brushed) the five grounds up in the engine compartment. Also what looked like a ground in the cabin. Reinstalled the battery, and retested... No Draws At All!!! Reconnected the fuse #17-Nothing! Reconnected fuse #29 (rear wiper/washers)-Nothing!! No Amp Draw, No Voltage Draw!! Calling this one "done" for now!!! (Until a couple days from now when the battery will be dead of course.....)

97grand4.0

Goodness where to start.

Check voltage with a meter and don't go by the dash meter which may be flaking out.

Voltage surges don't mean a bad alternator, unless the regulator is in the alternator. You have regulator problems.

Holding a 'good 12 v charge' is not good. Fully charged a battery is 12.6 volts. 12.0 volts is 90% discharged.

"0.5 to 0.9 mA when everything is off/sleeping" is outstanding. Actually I would expect more like 14mA. so I think you read it wrong.

"Fuse 17 (Cluster/Diagnostic Connector) is drawing 0.3 volts constantly, and fuse 29 (rear wiper/washer) is drawing 0.9 volts constantly. "
Well this is not possible because fuses don't 'draw' voltage.
The voltage across a fuse should be Zero if the fuse is good, and B+ if it is open or blown. You can check how much CURRENT is flowing through a fuse with a multimeter set to Amps.

i'm tired now.

dave1123

He's showing a voltage DROP across the fuse, meaning there is current flowing in the circuit. Somewhere I have a chart that relates voltage drop to amps, but IDK for the life of me where it is.

97grand4.0

If he is showing a voltage DROP ACROSS the fuse, that can only mean that the fuse has resistance.
The chart you are looking for is Ohm's Law, E = IR, or E/R = I. or E/I = R.

dave1123

https://us.autologic.com/news/how-to...nversion-chart

97grand4.0

Scratching my head on that one! At first I thought you had something, but I don't know who would write such an article or how it could pass muster.
I am analyzing why this has to be wrong. I'll get back to you after a few dozen cuppas.
Hey did ya check out the watchfire last night? I was there...what a crowd and the fire was scorching couldn't get within 100 yards of it so hot.

OK. So I learned something. Apparently there is some micro resistance in the little stab fuses that is exploited to look at the current through it. Useful if you have sensitive enough equipment to measure the resistance and not pick up stray signals in the microvolt range. Incidentally your average AM radio antenna picks up 200 microvolts with no trouble.

dave1123

Yeah, it kinda had me scratching my head as well, but it worked finding the parasitic draw in my XJ when I got it. I needed to use this method when I realized my DVM only read up to 200 milliamps. It seems my trailer module was drawing enough current to flatten the battery in 2 days. After removing it, the battery would start the beast after sitting for 3 weeks in single-digit cold! Of course it was a new battery because I replaced it first thinking that was the cause.

97grand4.0

Well in my world of 120v repairs all day long, a fuse or breaker showing a voltage drop would be a bad breaker and a hazard. But, I live and learn. I think the way this would be useful, is not so much to find the exact draw, but rather go down the fuses until you find one that IS showing a drop, something that seems to be more than the other at rest fuses, any drop more than the others, then investigate that circuit. Kind of a binary thing. Either good or bad.

dave1123

Yeah, that's what I figured out. At least that gave me the circuit to look at. The only fuses I got a drop on besides the brake light circuit was the one for the PCM memory. My beast doesn't have a dedicated IOD fuse. All the others showed 0 volts.

I couldn't make it to the watchfire because I'd need one of those 4-wheeled handicapped carts. I have trouble walking that far with no place to sit down afterward. I really didn't want to look like a disabled vet because my injuries are civilian and old age, not from combat. It's just a personal thing.

97grand4.0

The watchfire was amazing, yes you would have had to walk like 4 football fields, I did. I was impressed with how well behaved a crowd of 30k people was. No cops in sight either. Plenty of motorcycles tho.
The fire itself was like 6 stories tall. I brought an old flag to burn but it was going full blazes when I got there and couldn’t get within 100 yards of it for the pure heat. If they had fences up, they didn't , people would have been burned when the mob moved back. I could plainly smell it at my house when I got home some 4 miles away.