jpdocdave Posted August 9, 2009 Share Posted August 9, 2009 :smart: i gotta start by saying i've been a professional mecahnic for 8 years now and working on cars for many more, and i am pretty flippin good at electrical probs..... :( that being said.....i was installing a factory fog light harness, but i had to splice in just the fog light parts into my existing headlight harness, cuz the whole donor harness had one bad wire. so i figured i'll just splice the power wire for the relay and the green/black signal wire both for the factory relay, that are built into the factory engine side of the harness but dead end. anywho, i can't imagine what went wrong, i've been over what i did a few times, and i've removed the fog harness. here's whats happening, the ground circuits in the cab, and the circuit off the body ground on left front fender are being shorted, and getting 12 volts w/ the key on, or when i pull the headlight switch, or if i step on the brake pedal. any of these actions will engage the a/c clutch, and also run the fuel pump. :huh???: ya, its kinda cool actually. anyway things i've done that have made no change: pulled every relay pulled the wiring harness apart from firewall to headlights, no melts/shorts removed main bulkhead connector, checked and cleaned removed fuse box under dash, no probs, cleaned removed headlight switch ground (i really thought the switch was shorting power through the ground) but it wasn't disconnected computer disconnected ignition switch (thought that was it, but no change) disconnected headlight sentinal disconnected ever connector i could see just to try and isolate a circuit, still did it no matter what i do. i'm leaning to believe a power wire has to be shorting to a ground wire somewhere burried in the harness, but i was hoping to at least narrow it down. anyone think of anything else? :hmm: Link to comment Share on other sites More sharing options...
jpdocdave Posted August 9, 2009 Author Share Posted August 9, 2009 oh yeah, also checked all the fusible links at the ignition relay. Link to comment Share on other sites More sharing options...
Eagle Posted August 9, 2009 Share Posted August 9, 2009 Just to be sure I'm reading correctly -- it was NOT engaging in any of this before you tried to splice in power for the fog lights, correct? Link to comment Share on other sites More sharing options...
jpnjim Posted August 9, 2009 Share Posted August 9, 2009 If you have 12v dead shorts to ground, you should be either blowing fuses, or smoking wires. (are you?) How are you determining that your cab grounds are @ 12v (+)? (are you testing to some other ground, or to the battery, or ?) Keep in mind, if it's just a BAD ground, connecting a test light between the bad ground, and a good ground will light the light (and/or give you a reading on a voltage meter) With the key off, & the headlight switch/brake pedal switches in the off position are these grounds at negative polarity (-) like they should be? Since both the headlight switch & brake light switch energize the tailights, I would start there. The fuel pump & the tailights share a ground wire, I would make sure it's correctly grounded (common problem with MJ's). I would also look for a hacked up trailer light connection (first place I check with any funky wiring issues) It sounds to me like you have some bad grounds, and end up with stuff that share grounds in series with each outer, as the try to find good grounds. Link to comment Share on other sites More sharing options...
jpnjim Posted August 9, 2009 Share Posted August 9, 2009 Also, check to see that the ground jumper from the body to engine is in place. I'm betting if you ran a decent size jumper wire directly from the battery to that cab ground (when you are reading 12v there), it will not short out, and the problem will go away. (FWIW, I'm an electrician, but I absolutely HATE automotive electrical :nuts: ) Link to comment Share on other sites More sharing options...
jpdocdave Posted August 9, 2009 Author Share Posted August 9, 2009 Just to be sure I'm reading correctly -- it was NOT engaging in any of this before you tried to splice in power for the fog lights, correct? thats correct, so it is very hard to beieve its a coincidence. i went over the two wires i spliced, and also removed them. the two wires are there on the engine harness by the air box for the fog lights, the headlight harness just doesn't pick them up if the truck didn't have the option. Link to comment Share on other sites More sharing options...
jpdocdave Posted August 9, 2009 Author Share Posted August 9, 2009 If you have 12v dead shorts to ground, you should be either blowing fuses, or smoking wires. (are you?) How are you determining that your cab grounds are @ 12v (+)? (are you testing to some other ground, or to the battery, or ?) Keep in mind, if it's just a BAD ground, connecting a test light between the bad ground, and a good ground will light the light (and/or give you a reading on a voltage meter) With the key off, & the headlight switch/brake pedal switches in the off position are these grounds at negative polarity (-) like they should be? Since both the headlight switch & brake light switch energize the tailights, I would start there. The fuel pump & the tailights share a ground wire, I would make sure it's correctly grounded (common problem with MJ's). I would also look for a hacked up trailer light connection (first place I check with any funky wiring issues) It sounds to me like you have some bad grounds, and end up with stuff that share grounds in series with each outer, as the try to find good grounds. i think it is weird fuses aren't blowing, then at least i'd have a circuit narrowed down. i have an automotive test tool called a power probe. it hooks up to both sides of the battery, and it will show what you are testing if its power or ground, without constantly changing test points. i've back probed every ground in the cab, and they do not have a good ground with key off and so on, and get power with key on, brake pedal, headlight switch. i agree about the bad grounds in series, it is gonna find the path of least resistance, and looking at the diagrams, the factory really did some weird stuff with what circuits are shared, even factory spliced ignition power. thanks for the help, i didn't think about tailights, and grounds there. i'll look there to, i just can't believe its not something i did, but strange things happen on cars, but you gotta go where you were when something like this happens. Link to comment Share on other sites More sharing options...
jpnjim Posted August 9, 2009 Share Posted August 9, 2009 If fuses aren't blowing, I would definitely say it's a bad ground issue. When you read 12+ positive where there should be a ground, you are really reading through a load connected to that (bad) ground. (you are 'seeing' the hot on the other side of the load, through the load). If you put a volt meter on it, you should get some funky voltage less than system voltage (because the meter would be in series with the load, or loads). Their website says the Powerprobe has some kind of a bad ground detector, is it just an indicator light, or ? Link to comment Share on other sites More sharing options...
jpnjim Posted August 9, 2009 Share Posted August 9, 2009 i have an automotive test tool called a power probe. it hooks up to both sides of the battery, and it will show what you are testing if its power or ground, without constantly changing test points. i've back probed every ground in the cab, and they do not have a good ground with key off and so on, and get power with key on, brake pedal, headlight switch. This makes PERFECT sence. Turning the ignition/headlights/tailights/etc on increases the number of loads looking for that ground (that isn't there). If you connected a regular test light from the battery (-) to that ground point, the light would glow brighter & brighter as you increased the loads looking for that ground. Somehow, when you did the work, and/or replaced that bad wire, you must have disconnected the ground feeding that point. Check your (-) to body connection (should be a jumper to the engine), or even just temporarily jump the (-) terminal to the body. Link to comment Share on other sites More sharing options...
BlueXJ Posted August 9, 2009 Share Posted August 9, 2009 Is it possible that you selected the wrong wire when making your splice and are now trying to ground a constant hot wire. Link to comment Share on other sites More sharing options...
jpdocdave Posted August 9, 2009 Author Share Posted August 9, 2009 i have an automotive test tool called a power probe. it hooks up to both sides of the battery, and it will show what you are testing if its power or ground, without constantly changing test points. i've back probed every ground in the cab, and they do not have a good ground with key off and so on, and get power with key on, brake pedal, headlight switch. This makes PERFECT sence. Turning the ignition/headlights/tailights/etc on increases the number of loads looking for that ground (that isn't there). If you connected a regular test light from the battery (-) to that ground point, the light would glow brighter & brighter as you increased the loads looking for that ground. Somehow, when you did the work, and/or replaced that bad wire, you must have disconnected the ground feeding that point. Check your (-) to body connection (should be a jumper to the engine), or even just temporarily jump the (-) terminal to the body. i will jump the ground to make for sure. but i'm thinking the same about your last statement, i think i lost a ground on accident when doing this. thanks for the help. its alwasy good to bounce ideas around Link to comment Share on other sites More sharing options...
jpdocdave Posted August 9, 2009 Author Share Posted August 9, 2009 Is it possible that you selected the wrong wire when making your splice and are now trying to ground a constant hot wire. i'm 99.99 percent sure. it was very straight forward, and i just removed a harness from an mj being parted out, and i had the whole headlight harness to match it up to. the larger red wire was a constant power for the fog light relay. and the green/black tracer is the switch signal. that was all. and like i said, i undid that stuff first so it was back to normal till i figure this out. Link to comment Share on other sites More sharing options...
mnkyboy Posted August 9, 2009 Share Posted August 9, 2009 grounding a constant hot would be blowing fuses or melting wires. my nieghbor came to me the other day saying his XJ was running bad and doing weird things, he also said his transmission was going out. a few days earlier his old crusty battery cables had shorted together and melted the chassis ground strap,i replaced it and everything has been fine since. he had battery neg (-) to engine block and a strap from the engine to chassis and that was it,with the strap burned he had no continuity from the battery to chassis making everything go hay wire. I guess poor grounding is just part of our wonderful Jeep electrical system,I would also check the grounds and think about adding some extra grounds Link to comment Share on other sites More sharing options...
jpdocdave Posted August 9, 2009 Author Share Posted August 9, 2009 i did check the ground straps and made sure the engine and body grounds were good. Link to comment Share on other sites More sharing options...
mnkyboy Posted August 9, 2009 Share Posted August 9, 2009 don't know if you have a schematic but are there any junctions in the harness near where you were working? sometimes the factory will solder a bunch of POS(+) or NEG(-) together in the harness,Ive seen these get corroded over time or break loose and cause problems like your having. Its possible you may have disturbed something further down the harness Link to comment Share on other sites More sharing options...
jpdocdave Posted August 10, 2009 Author Share Posted August 10, 2009 don't know if you have a schematic but are there any junctions in the harness near where you were working? sometimes the factory will solder a bunch of POS(+) or NEG(-) together in the harness,Ive seen these get corroded over time or break loose and cause problems like your having. Its possible you may have disturbed something further down the harness i have checked this also. the wiring on this thing is whacked from the factory. i have the schematics, and i have found factory splices in the harness to check them. there is a factory splice for ignition power all coming together and it feeds the fuel pump, a/c clutch and a couple others that are powered up at the wrong time. same with some grounds, i pulled the harness apart to find them, and they are fine. its amazing, they didn't solder them from the factory, just clamped them together, and duct taped them. and it is factory, i've seen on the other harness i took apart to, undisturbed till i got to it, factory duct tape and wires just clamped together :nuts: thanks again everyone, keep the ideas coming. i've been hanging with the family all day so i'm going at it again tomorrow. Link to comment Share on other sites More sharing options...
jpdocdave Posted August 10, 2009 Author Share Posted August 10, 2009 so here's where i got back to it today Image Not Found Image Not Found Image Not Found many thanks to all that helped. i took some good advice and jumped some of the grounds. the main ground from battery to block was good. but when i jumped any body ground to the battery ground problem went away. weak body ground was the culprit, i had to go back to where i was and go that direction, its just to coincidental, but that happens. i didn't screw anything up, i can't even imagine that i disturbed anything, but its possible. so here's what i did. i ran a ground cable from battery to body Image Not Found this fixed the problem, but i ran another cable from the manifold to the body just for insurance Image Not Found Link to comment Share on other sites More sharing options...
mnkyboy Posted August 10, 2009 Share Posted August 10, 2009 those grounds should work alot better then the factory ones. glad you figured it out :thumbsup: Link to comment Share on other sites More sharing options...
CWLONGSHOT Posted August 10, 2009 Share Posted August 10, 2009 Glad you have figured this one out!! I have said all along, extra/new grounds are a VERY GOOD THING!!! CW Link to comment Share on other sites More sharing options...
jpdocdave Posted August 10, 2009 Author Share Posted August 10, 2009 yep, its cool to be right :yes: everyone was a lot of help, and a couple people did say this could be it. anyone in my position would have had to retrace their steps though, its just so flipping coincidental. you always gotta go to where you just were when something goes wrong, 99 times out of 100 you did something. thanks again to everyone. Link to comment Share on other sites More sharing options...
HOrnbrod Posted August 10, 2009 Share Posted August 10, 2009 Good work - glad you got 'er done. :cheers: Those coincidence things can drive you crazy. How about the factory el-cheapo braided ground strap from the back of the head bolt to the firewall? I also replaced that one with a cable since a lot of stuff uses the firewall for grounding. :D Link to comment Share on other sites More sharing options...
CWLONGSHOT Posted August 10, 2009 Share Posted August 10, 2009 yep, its cool to be right :yes: In re-reading my post it kinda comes off like I'm blowing my own horn. Please be assured, that's not the case. In fact I didn't even offer a suggestion to your problem. I did read the post, but as I didn't have any better suggestions than the ones offered, so I didn't comment. (I really am glad you found it out.) My reason for commenting now, was just pointing out that many problems not immediately apparent as electrical/grounding issues, can be remedied with new/ better electrical grounds. CW Link to comment Share on other sites More sharing options...
jpnjim Posted August 10, 2009 Share Posted August 10, 2009 A very similar (and confusing) thing happens when you don't ground building transformers. So a good rule of thumb (in cars & buildings) if you're getting screwy readings, and can't track it down, check your grounds. :D I'm glad you got it straightened out. :cheers: FWIW, what are you gonna wrap the harness in now? They make non-sticky tape for that (sticky electrical tape isn't the right stuff to use). Link to comment Share on other sites More sharing options...
jpdocdave Posted August 10, 2009 Author Share Posted August 10, 2009 FWIW, what are you gonna wrap the harness in now? They make non-sticky tape for that (sticky electrical tape isn't the right stuff to use). i shoved it back in the plastic tubing, i did use some regular old electrical tape to bundle them together at places. i'm always interested in learning something better, whats the right thing to use? Link to comment Share on other sites More sharing options...
jpdocdave Posted August 10, 2009 Author Share Posted August 10, 2009 yep, its cool to be right :yes: In re-reading my post it kinda comes off like I'm blowing my own horn. Please be assured, that's not the case. In fact I didn't even offer a suggestion to your problem. I did read the post, but as I didn't have any better suggestions than the ones offered, so I didn't comment. (I really am glad you found it out.) My reason for commenting now, was just pointing out that many problems not immediately apparent as electrical/grounding issues, can be remedied with new/ better electrical grounds. CW naw, i didn't think it sounded that way, i was just being funny since most people post these threads then one of two things happens. 1- there is never a fix posted so its a mystery, or 2 they come on saying hey i got it, i figured it out, and it was something someone said a long time ago :D Link to comment Share on other sites More sharing options...
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