moship

I’m in the process of building a wiring harness to improve headlight brightness similar to the ones found through out this site and others, but ran into a problem I didn’t anticipate with the stock light circuit.

1st off it is a 98 Cherokee with factory fog lamps, but not day time running lights or security alarm. With both head lamps removed I wanted to test the voltage output of the three headlamp wires to verify they would trigger the relays being added to the system. At this point all wiring is stock, but the headlights have been physically removed from the circuit.

With the stock light switch on and the dimmer switch in the low beam position something strange happens: (measured at stock female headlamp connector)
Ground reads near zero, Low beam reads near battery voltage, but there is 6 volts showing on the hi beam circuit!!!
With the dimmer switch in the high beam position: Ground reads near zero, Low beam reads zero and high beam reads near battery voltage as one would expect.

The problem is the 6 volts showing on the high beam circuit when it should be in the off state. Why is this a problem?… There is enough voltage & current back feeding through this circuit to trigger the relay to the on position.

Some additional info to confuse matters worse. When the stock fog light mini relay is removed from the underhood fuse box the voltage drops from approximately 6 volts to 3 volts on the high beam circuit when in the off state.

• Does anyone know why this is happening and provide a solution?
• Does anyone have a wiring diagram that I might be able to use to decipher where this might be coming from?

I noticed in some of the other headlamp/harness conversion threads people seemed to experience problems when dealing with later model years. Did something change in the elelctrical circuit around 96, 97 or 98?

Thanks in advance for your help!

1armyguy

I can't say why that is happening but, I did purchase the upgraded wiring harness from eautoworks.com and installed it with new silverstars and what a difference. Works great for me. I took the grill of to run the wiring in front of the radiator and attached it to the stock wiring harness to keep it from hitting the radiator or other sharp areas. Easy install. Had to remove the battery and tray to get the wiring through but, wasn't a hard job.
Good Luck

moship

I still need help, but here is an update.

The homemade harness has been installed and works flawlessly as long as the factory fog lights are removed from the wiring circuit. This is accomplished by disconnecting the fog light relay. The head lights are very bright now with full voltage, but I'm very disappointed to have the fog lights inoperable.

I know it is possible to rewire the fog lights to isolate them, but there has to be a solution that will allow the fog lights to operate with the wiring upgrade.

I'm hoping someone can shed some light where this stray voltage is coming from or a wiring diagram for 98 and new vehicles including the fog light circuit.

FYI. I did check the fog lamp switch in the center stack and it works correctly. In an older model I actually experienced a factory switch that melted.

Regards

4Loco

I've heard about the factory switches melting. I just bought my Cherokee a few days ago and began gleaming the internet for info so I can learn the ins and outs of Cherokees. Apparently, your year jeep had many different wiring harness configurations. As in the factory changed the harness design more than once during a model year production. It's possible that you could have one of the harnesses that inadvertently had back flow issues that were later corrected with a different harness.

As for wiring diagrams, you can't beat Mitchell! When I was working at firestone, we used mitchell for our tsb's and recall info, it was very detailed and elaborate. I highly recommend purchasing a week subscription and printing up the wiring schematics. BUT, if what I read is true about the numerous different possible designs, it could get messy.

freegdr

have you installed a new relay and see if that stopped the 6volt issue

moship

Freegdr,

I replaced both the factory relays located in the power distritbuiton center located under hood and the relays on the new wiring harness.

With the fog light relay installed (stock circuit) the leakage current is approximately 42mA on the high beam circuit when the low beams are on. The leakage current doesn't change when the fog lights are on or off. This leakage current is enough to get funky results on the high beam indicator located in the dash. (funky meaning dim glow that is always on)

Does anyone have a 98 or newer jeep with factory fog lights that could check the amount of stray voltage/current in the factory wiring? I'd love to know if this is due to the design or something wrong with my wiring harness and switches.

98jeepsrt6

I have a 98 with factory fog, no security, etc.. When i get off of work today ill go ahead an do that test for you..

Just to be clear its the female plug for the headlight assembly.. And ill be testing all three wires that lead to the connector. (1) Ground , (2) Low Beam, (3) High Beam/ Which is where you have the stray voltage.

So ill get back to you prob around 3ish with what results i came out with.


Is the stray voltage on both plugs are only one??

freegdr

relay has to be back feeding maybe run seperate power wire to fog relay

moship

98jeepsrt6,

Thanks for the offer. Both headlights have to be disconnected from their harness, so there is no load on the stock headlight wiring. Measure the voltage at all three female terminals (connector that plugs into head light) with the light selecter switch on Low Beam. It doesn't matter if it is the passenger or drivers side.

Mine will read near battery voltage on the Low beam circuit and approximately 6 volts at the high beam circuit. It's crazy the way this is.

I look forward to seeing your results!

Other: I have thoroughly tested the various relays and it is not a relay problem.

gmv93

for 97 GC, i found a 9007 conversion mod and i did it. actually it is more than cutting and resoldering wiring harness, including cutting slits to bulb base with dremel tool to fit bulb. anyway,

when i copied what i saw on internet to do this mod, after soldering wires exactly shown on photos, low beams were dim, like "6 volts". i tried all combinations on wires and found the correct wiring order(now low beams are bright and high beams are weaker but all are in 12 volts) i dont know how this is possible or why is so, but it is.

yours can be related to the wiring order.

4Loco

I abstracted this from my Haynes manual, hand-wrote it so I could get a feel for it and so the diagram doesn't have other stuff next to it that clutters up the image.

Hope this helps!!


::EDIT::
Crap! I forgot to label the color of the wires in the circuit.
Not sure how accurate haynes is with wire colors though.

moship

4Loco,

Thanks for taking the time out to think about this and provide the drawing.

If the insulation was breached in the proposed area I would expect to get a similar leakage current on the low beam side when the hi beams were engaged. On my vehicle this doesn't happen. What are your thoughts on this?

Here is another piece of information that may help given your wiring diagram.

With the fog light switch in the center stack completely removed from the wiring circuit there is no difference in the leakage results. If the drawing is accurate it seems removing the fog light switch would eliminate any of this wiring from the problem. I'm wondering if there is a problem in the power distribution center. Has anyone ever taken one apart to see what they look like inside? Can it be dismantled?

I'm beginning to wonder if the voltage drop is associated with some type of diode (or LED) or other solid state device in this circuit. Then again an abraded wire or other leakage path could be happening.

It has been frustrating trying to figure this out and I want to thank everyone for their input and help. I'm certain with the collective brainstorming the root cause will be uncovered.

4Loco

I hear that for a given model year, between 97-99, Jeep was trying to figure out the harnesses, so they came out with a different harness design multiple times per production year. Perhaps for your iteration, they tried some haphazard way of making the fogs stay on while the hi beams are on. This might have a factory leakage from the low circuit into the high.

Perhaps the fog light, or switch indicator shares a ground with the headlights. Or possibly the ground for the relay shares with the headlights. That would explain backflow into the headlight harness via the high beams. Auto manufacturers often try to share common grounds on the chassis to reduce RF noise, but this might be one of those cases where the engineers didn't bother with Kirchoff's loop laws. Haha, I don't necessarily blame them, I forgot the procedure for analysing circuits that way.

Either way, If you do so decide, you'll have brighter lights by giving each component a dedicated ground, they will be much more reliable, especially if you decide to fuse protect at each critical junction. A bit overkill, I suppose, but it'll handle power surges fairly well.

lilredxj99

The fog light relay coil grounds through the HI side of the DS head light. Nothing complicated about it... when the fog light switch is on and the hdl's are on low it grounds the coil and the fog lights come on. When the HI comes on, the relay no longer grounds through the HDL, instead it is back fed w/ 12v.

Nothing magic and not multiple wiring. The new kit to repair the fog light switch includes a relay that is close to the switch, and all it does is take the load off of the switch.

If you run a harness, clip the wires at the ds factory headlight connector, and locate the one w/ 6v w/ low beams on and fog light switch on. Should be brown/white.. Now you can do 1 of 2 things.

1. Take this wire and ground it, and the fogs will work with low or hi beams.
2. Take this wire and splice it into the HI beam side of your aftermarket harness, and the fogs will work just like factory. Low beam on, fog light on... Hi beam on fog light off.

moship

Lilredxj99,

Thanks for the great lead. I'll have to go with option #2 to pass PA inspection.

One question. What does DS mean?