Electrical Issue

[HB Chris]

I was working on the Chamonix project and bumped a fuse with a wrench which caused a small spark. No fuses burned, all wires fine, no wires disconnected from back of the fuse holder/junction block. Now I only have less than 4 volts from the battery on the large red wire (all red ones from the battery) inside the cabin that goes to the junction block and continues to the ignition switch. Nothing works or lights up, everything was working before so now I can’t start the car or do anything. Battery is new and fine with 12.3 volt. Very strange and very disconcerting as wiring is one of those issues we deal with on a coupe but are nightmare to identify and resolve. And all I was doing was removing extraneous wires that were tapped into the existing harness that every coupe seems to have!

On a side note, I have a brown ground wire that goes from rear fog switch (not present) to the wiper relay to the load shed relay and into the harness bundle and includes the turn/hazard relay that is fried so it obviously shorted to a hot wire somewhere and melted all along its length. Almost everything in the dash shares at some point a common brown ground wire. This one is going to be a challenge as it is so hard to open up the harness while in the dash, wish me luck. I think I will look for continuity in every positive wire to see which one was shorted out.

Can you tell I hate working under the dash?

 

[Thomas76]

Bugger! Might try pulling the battery then check resistance on a few wires in the area. Or connect a length of wire direct to battery, using that as a constant for probing around with a meter. Either way the problem will be on the very last one you check.

 

[Markos]

Ugh. Did you actually drop the fuse block down and examine the backside? I presume so given the work that you mentioned. I had the exact same issue after pulling my extraneous wiring. I pulled something near number 10 off the terminal.

Did you test the voltage at the battery just to rule that out? Seems somewhat “impossible” to read 4 volts on the battery side if your battery is putting out 12+.

 

[HB Chris]

I dropped the fuse block, checked every spade, checked every red wire with a max of four volts. Voltage at battery is 12.3 volts whether ground strap is connected or not, there is no drain on the battery as I left it connected the last several days.

 

[coupesport]

So you momentarily shorted the battery side of a fuse? Current surged to/thru that point. You now have a large voltage drop through only the red wire or its junctions/lugs /connectors in that path. Time to clean all contacts.

But perhaps first pull the fuses 1 by 1 while monitoring to see if something in parallel path was damaged.

 

[HB Chris]

No power is getting to the fuses, I tested with a meter upstream from the fuses.

 

[coupedegrace]

And all I was doing was removing extraneous wires that were tapped into the existing harness that every coupe seems to have!

I've managed to get many electrical things working that weren't when I got the car, but I've been reticent to try and get rid of the extraneous wires. I imagine somehow arc welding something even if I pulled the battery. Good luck with your detective work!

 

[Krzysztof]

I would start with battery clamp. It could be coincidence but sometimes they are oxidized.

Next the starter motor cable and alternator/generator cable. There two have direct connection from battery.

For me it looks like red wire was just "hanging" on a thin contact due to mechanical reason or oxidation, so current surge make it blown away.

Another step is to check where red wire is starting it way from battery (alternator?).

If there is no KL30 (DIN naming for permanent battery line) you will not run the car as there will be no power to energize contact relay on the starter motor even if the battery itself is charged.

Same story might be for brown wire (KL31). If the path is highly resistive no chance to start the car.

Playing with test bulb, continuity tester/ohmmeter is the way despite it is difficult and time consuming, but start with easily available contacts in the engine bay (including relay box) and follow that path till the firewall input/output in in the interior.

Good luck!

 

[Willem Tell]

Hi Chris, if you bumped a fuse and then had a continuous drop in battery voltage, I would suspect that the short pulled too much current through a diode (across a relay or device). The shorted diode is now providing a path to ground.
I looked at the circuit diagram, and typically the relays don't have bounce-protection diodes. Sometimes people add diodes to relays (if the window mechanisms have been changed to E28 for example).
Since you're not popping fuses, it is likely something between the battery and the input side of the fuse block.
Possibly the alternator or voltage regulator diodes, or there might be a diode built into the starter bendix coil, but I don't know for sure.
I would start by disconnecting the starter, alternator, and unplug the voltage regulator near the battery. Then switch on and check for +12.xV. If battery voltage checks good, it's likely one of those.
If not, I would suggest taking a photo of your fuse block so you know which type of fuse is in each holder, and then remove all fuses. Replace the fuses one-by-one while observing your battery voltage. If you find a fused circuit that pulls down the voltage, leave that one out and continue replacing the others. That should help you narrow it down.
If you can identify one circuit, start checking if any relays have diodes on their sockets, or sometimes relays have an internal diode (pull the relays). Once you know which fuse circuit is faulty, find a place on that part of the harness where you can physically feel the wires for heat. A shorted diode (or a shorted wire) will be hot enough to take the skin off your finger, so be careful!
Hope that helps.

 

[Krzysztof]

Looking on the schematics there are few wires starting same point.

By checking all the items (blue boxes) you can determine which wire is the root cause:

I excluded light relay and generator but they can also be examined once the other wires will be OK but according to text it should be one of the interior going red wires.

31 is diagnostic connector, so can also be easy accessed from under the bay.

 

[adawil2002]

I empathize with your electrical frustration, Chris.

Need a wire line tester to find any broken wires.

Note to self, disconnect the battery when working cleaning up previous owners's electrical stuff.
Your car can injure, burn or kill you. I know a few people who have gotten 3rd degree burns from their watch grounding, gets hot fast.

 

[sfdon]

Measure for Battery + at red wire to ignition switch with key off.
measure for Battery + at Green wire from switch with key on

 

[HB Chris]

No power at ignition switch, period. Going for a bike ride.

As you can see, one red wire goes to the junction block with five wires, I have no power there. Another red goes to input side of fuse 5, I have no power there. The last even larger red wire goes to the Alt, that is not in play here. One goes to the load shed relay which sheds loads during cranking, it doesn’t provide power it removes it from other consumers. I will tackle later this afternoon.

 

[sfdon]

I’m home- call if you want resistance readings.

 

[Krzysztof]

No power at ignition switch, period. Going for a bike ride.

As you can see, one red wire goes to the junction block with five wires, I have no power there. Another red goes to input side of fuse 5, I have no power there. The last even larger red wire goes to the Alt, that is not in play here. One goes to the load shed relay which sheds loads during cranking, it doesn’t provide power it removes it from other consumers. I will tackle later this afternoon.

Is any point with battery except battery itself where battery voltage is available?

May I ask where the negative terminal of the voltmeter has been connected? My question is coming from the possibility that the battery voltage is there but there is not negative/ground. The effect on the meter will be the same. The only reason is typically car has many GND points, so for low load as the voltmeter is, the voltage should be still in range.

In case there is no voltage on starter and generator nor diagnostic plug the problem will be with the battery clamp probably.

 

[coupesport]

have a brown ground wire that goes from rear fog switch (not present) to the wiper relay to the load shed relay and into the harness bundle and includes the turn/hazard relay that is fried so it obviously shorted to a hot wire somewhere and melted

reread and noted "melted". Your return/ground path most likely culprit. If your confident in reading schematic you can jumper in a temp/parallel return path but you'd want to be sure this jumper landed on the same ground junction as does this brown wire where it exits the harness bundle on the far end. This is tricky work so triple check or 2nd set of eyes before doing. Also before battery connection you might try and read the ohms on this suspect return path with and without the temp/parallel jumper - however a damaged/resitive path sometimes measures well since the ohmeter uses only trickle current as comared to real amperage. But the ohm meter may show a telltale.
I'll take a look at the schematic.

 

[Krzysztof]

BTW

Few watt bulb-based, simple tester is giving more confident readings than any digital, universal multimeter in voltage readings.

 

[HB Chris]

Is any point with battery except battery itself where battery voltage is available?

May I ask where the negative terminal of the voltmeter has been connected? My question is coming from the possibility that the battery voltage is there but there is not negative/ground. The effect on the meter will be the same. The only reason is typically car has many GND points, so for low load as the voltmeter is, the voltage should be still in range.

In case there is no voltage on starter and generator nor diagnostic plug the problem will be with the battery clamp probably.

When tapping into the large red wire behind fuse block (in three different places) I used several different grounds for the meter: door sill screws, door switch screw, bolt holding hood release handle.

 

[HB Chris]

reread and noted "melted". Your return/ground path most likely culprit. If your confident in reading schematic you can jumper in a temp/parallel return path but you'd want to be sure this jumper landed on the same ground junction as does this brown wire where it exits the harness bundle on the far end. This is tricky work so triple check or 2nd set of eyes before doing. Also before battery connection you might try and read the ohms on this suspect return path with and without the temp/parallel jumper - however a damaged/resitive path sometimes measures well since the ohmeter uses only trickle current as comared to real amperage. But the ohm meter may show a telltale.
I'll take a look at the schematic.

Thanks. Fried brown wire was in car when purchased and everything not connected to it worked: parking and head lights, instruments, tail lights, ignition, etc. Hazard relay was removed as I’m sure the fried wire is connected there too.

 

[Ohmess]

Hi Chris - I think Willem's suggestion is most likely. Melted wires providing a path to ground would provide a complete short, not an 8 volt reduction in current. With no parasitic drain, battery voltage at 12+ and a big voltage drop to the fuse block, I would concentrate on the diodes in your voltage regulator first. Isolate those diodes from the rest of the car and then check your voltage at the fuse block.

Next best guess would be your load shedding relay. Remove the relay and check the current at the back of the fuse block.

Oh, and when chasing melted wires, remember that they melt at the ends where resistance is highest. The point of this is when you find one end that is melted, check the other end. It is likely melted too.