Dead "batt" circuit at the fuse block

[MJR]

Actually, the best way to wire every circuit in the xj would be with a separate fused wire from a source near the battery but this is, of course, not practical.

Well early ones 84-90 used main fusible links and 91-01 used Maxi-fuses near the battery. Oh and one other thing you might not realize is that the ground wires are also smaller than the positive for a reason.

 

[winterbeater]

Well early ones 84-90 used main fusible links and 91-01 used Maxi-fuses near the battery. Oh and one other thing you might not realize is that the ground wires are also smaller than the positive for a reason.

Please don't keep us in suspense! Why are the ground wires smaller?

 

[88 Wagonman]

Please don't keep us in suspense! Why are the ground wires smaller?

My guess would be that they are shorter runs, so they don't need to be as big, but since there is some mystique in your posting this I am assuming that that's not the reason.

 

[MJR]

Please don't keep us in suspense! Why are the ground wires smaller?

Serious it matters? LOL. It's another way of circuit protection. If the fuse fails (or because someone put a larger fuse in it, like that ever happens), and the main fusible link/fuse fails, then the ground wire is the next to go before the rest of the wiring burns up.

 

[88 Wagonman]

I disagree with that entirely, site your source (or is it speculation). I have seen many circuits without fuses fail (customer's bad wiring on several occasions) and the grounds were untouched.

 

[MJR]

I disagree with that entirely, site your source (or is it speculation). I have seen many circuits without fuses fail (customer's bad wiring on several occasions) and the grounds were untouched.

I'm not saying it always works out but it makes sense (especially since it's funny how quickly people think engineers don't always know what they are doing) and based on my 16 odd years as an automotive electrical mechanic. It is stupid to always think someone knows better than the engineer when they have know idea what the parameters are. There is more to be considered. I too have seen times where the harness burnt up (usually same size wiring on high load circuits like one I had with the rear defroster). Take it as you will.

 

[88 Wagonman]

I'm not saying it always works out but it makes sense (especially since it's funny how quickly people think engineers don't always know what they are doing) and based on my 16 odd years as an automotive electrical mechanic. It is stupid to always think someone knows better than the engineer when they have know idea what the parameters are. There is more to be considered. I too have seen times where the harness burnt up (usually same size wiring on high load circuits like one I had with the rear defroster). Take it as you will.

I am not trying to belittle your experience, please don't take it that way, I can only site what I know about this subject on a personal experience basis since I was not part of the original design team for Jeep and I assume you were not as well. So what I am saying is that it is speculation on both of our parts, the difference is that you are saying it as if it were fact that that is the reason, which is why I asked for a source.

I agree with you about people thinking that they know better than the engineer, I hate that, but I just don't think the grounds add circuit protection. Maybe an experiment is in order?:shhh:

 

[MJR]

So what I am saying is that it is speculation on both of our parts, the difference is that you are saying it as if it were fact that that is the reason, which is why I asked for a source.

I am trying to get people to think about things. There's always more then meets the eye as they say. It's kinda like the thread on the HVAC doors. Most people do not realize all the things an engineer takes into account. Things that go on as the design passively.

I can remember one such thing with the NS (1996-00 Chrysler/Dodge minivan). It was explained to us that if a customer gets into the hot vehicle (been sitting in the sun) and turns on A/C then selects the recirculate function it will appear to the customer it did so. But in fact the controller locks out the recirculate function for a few minutes to flush the hot (hotter than outside) air out of the vehicle (flow through body vents at the rear of the vehicle). This is just one of those things that goes into a car design that's smarter than the average consumer.

 

[kastein]

OK, hasta a large cable in good condition will have a very low resistance (OHMS), in comparison a large cable with every strand but 1 still making a connection or in this case intermittently making one will have a very high resistance, this will make troubleshooting very easy and definitive. Just simple electron theory.

Voltage drop is a measure is what?..... hmmm resistance yeah that's it. So a test that measures voltage drop is a test of what?....hmmm oh yeah resistance sorry.:shhh:

Stop being a wiseass about this, it's kinda annoying. Yes, it'll have a slightly higher resistance, but did you know that most metals have a positive resistance thermal coefficient? i.e. they get more resistive when heated? That means that under load, the wire has more resistance and... less current will flow. Measuring voltage on automotive electrical systems is far more accurate a diagnosing tool than measuring current. Also, remember that for stuff like headlights, the light output is proportional to the cube of the voltage supplied, rather than being first order... this means that a tiny variation in supplied voltage shows up as a LARGE difference in brightness. So let's see, a crappy connection in a wire carrying 7 amps to a headlight, say it's half an ohm of resistance in the connection. That's going to drop 3.5 volts :looser: (you know ohm's law, right? You seem to think you know everything about electronics, or "electron theory" as you call it) you now have approx 10 volts at your headlight, how bright is it going to be? Not very. Yet you put your ohmmeter on the wire and say "well my meter says .7 ohms, .2 of that is the test probe leads, half an ohm, not bad, problem must be elsewhere."

OP - "divide and conquer" is the best method to take with electrical issues. Get yourself an FSM or if you really can't afford it, make do with a Haynes manual. Find the circuit you're having problems with, find all the connectors on it and accessories powered by it, start by unplugging the furthest upstream (toward the fuse/battery) connector you can find, check if you have a good voltage reading after doing that. If you don't, it's between the last place you measured upstream and where you are now. If you do, plug that back in and move down the chain. Keep doing this till you find what section or accessory is causing the problem, repair as needed.

 

[krochus]

OP - "divide and conquer" is the best method to take with electrical issues. Get yourself an FSM or if you really can't afford it, make do with a Haynes manual. Find the circuit you're having problems with, find all the connectors on it and accessories powered by it, start by unplugging the furthest upstream (toward the fuse/battery) connector you can find, check if you have a good voltage reading after doing that. If you don't, it's between the last place you measured upstream and where you are now. If you do, plug that back in and move down the chain. Keep doing this till you find what section or accessory is causing the problem, repair as needed.

While as a rule of thumb I agree with this assessment I will say that the amount of effort I put into a vehicular repair is directly proportional to how much I have tied up in the vehicle and how much longer I expect it to last. In fact at this point and age I'm quite reluctant to disturb the main fuse block connection at all.

$800 + 257K miles = I'm just going to pull a fuse, make a couple crimp connections and provide for another route of power supply.

I'm not an electrical noob, I've made my own TBI fuel injection retrofit systems from boneyard parts and whittled down factory harnesses but LOL sometimes it's just easier to just run a new wire

 

[MJR]

sometimes it's just easier to just run a new wire

If it works for you that's cool but I'm just not wired that way (LOL) and would prefer personally to find/fix the problem. I've had to fix a few on the XJ's I have owned. I think the most expensive XJ I have bought to date was $1,250.

 

[krochus]

Most people do not realize all the things an engineer takes into account. Things that go on as the design passively.

since we're already waaaaaaaaaaaaaaaaaaaayyyyyyyy OT already

I would like to make a good natured counter to this if I may that engineers are indeed not infallable and sometimes overlook major issues with a design element

case in point- the in bellhousing slave cylinder

the engineer who came up with this abomination should be drug out in the street and shot

 

[kastein]

I'd like to add the guy who put the E12 inverse torx screws and the CPS on top of the bellhousing to the list of those who should be drug out and shot.

Maybe the one who thought it was a good plan to put the belt tensioning bolt on the 91-93 underneath the PS pump, too...

I definitely understand the "screw it, patch it till it works" mentality, I've had to do that a few times, though I much prefer a clean OE repair when I'm not too frustrated to do it.

... reminds me... at some point I should actually bolt the front edge of my front skidplate to the crossmember

 

[MJR]

I would like to make a good natured counter to this if I may that engineers are indeed not infallable and sometimes overlook major issues with a design element

case in point- the in bellhousing slave cylinder

the engineer who came up with this abomination should be drug out in the street and shot

It wasn't meant to suggest that they aren't human. One of the frustrating things for me has been seeing repeated mistakes which comes with new engineers every period of years I have noticed with Chrysler.

While that type of slave is not easy to change it works ok as long as the pressure plate doesn't cause problems.