traxtar928

As a few key members on here might know (I've reached out for some assistance already), I've been having some strange voltage issues. The car has needed a jump on a few occasions recently, with no reason as to the cause. Sometimes it would need a jump every time I drove it, and sometimes it would start right up. Battery and alternator test at a local parts store said they were both fine. Relays at the fuse panel are all cold to the touch at a cold start up. Grounds are all good, visually.

In addition to the car not wanting to start occasionally, the voltage was very inconsistent. Indicative of a bad voltage regulator. Voltage while driving ranged from 13.3v to 11.3v, depending on if headlights were on. At stop lights, the voltage would slowly drop to 10.5v while the headlights (and brake lights) were on. While driving, voltage would stay at 12.2v (with a fluctuation of 0.7v). Those voltages were measured by the multimeter display on my hard wired radar detector, not the jump post.

Unable to pinpoint the cause, I recently installed a new Bosch alternator (thanks to Roger and Laura for quick part availability). Regardless of that being the cause of the issues or not (I pretty confident it's not), it was time for replacement as the voltage was never steady and I have no record of it ever being replaced before I owned the car 5 years ago, so it had at least 80k miles on it.

For a sanity check, I ran long leads into the car from the jump post, connected to my fluke dmm. Now that I have the new alternator on, voltage while driving (with headlights off and minimal loads - radio, blower, etc) is rock steady at 13.5v volts, measured at the post. If I have the headlights while driving, the voltage drops to 12.7V. When I stop at a stoplight (headlights off, minimal loads), the voltage drops to 12.3v. If I turn on the headlights while stopped, it will further drop to 10.8v. So the issue was not fixed by an alternator replacement.

Do these issues point to the need for a new wiring harness? Anyone have similar issues they noticed? If so, what was your repair? I'm out of ideas.


Harness in its current state




Sensor wires with brittle insulation

Speedtoys

Next best candidate, is replace the ground strap in the rear...and clean/check battery + connections.

The ground straps can LOOK good, but be a huge problem under the insulation.

LT Texan

Any chance you can measure the voltage at the alternator post at different loads?

But if you are measuring the voltage at the jump post, that implies that your alternator is not putting out the juice.

Or that the cable from the alternator post to the jump post is resistive.

Always good to clean the grounds as Speedtoys says.

traxtar928

I'm looking at this Waytek ground strap I've seen people use:
https://www.waytekwire.com/item/36282/

And I purchased 15 feel of this UL-1426 rated 1 AWG cable for the positive connection to the starter:
http://www.genuinedealz.com/media/ca..._Specs_BBW.pdf

Next I'll be replacing the engine ground strap and the engine/alternator/starter harness with one of Sean's.

Something is definitely not right with the voltage... I recently installed Euro H4 lenses, and measured luminosity of the included Dr. Fischer bulbs to compare to my stock H5 bulbs, and they were actually dimmer! Also, lately I can't get the fog lights to turn on until I rev the engine (then they stay on). So, somehow I'm not getting enough voltage to charge the battery and the headlights aren't getting the best voltage either.

GlenL

Clean the ground points

LT Texan

I've looked not he current flow charts, but I don't know if there is a resistive point after the jump post cable connects to the CE panel.

Does it go through a main relay, or the ignition switch?

If so, could this cause the voltage drop?

traxtar928

Ground points are all clean, but I can check continuity.

dr bob

Similar symptoms on mine lead me to replace the positive cable, go through and clean the grounds again, and do a LOT of measuring with long wires and such, trying to identify the voltage drops.

Drum roll.... Replacing the ground cable was the answer. The cable measured fine with the meter, no drop apparent while charging, but there was enough resistance to keep the battery from fully charging, and also from delivering full current under low-RPM loads. That little cable was less than $25 from our vendors last I looked.

Replace the engine to chassis ground cable too at the same time.

gazfish

Where are you grounding the DMM when you're measuring the voltage at the jump post, if you've got grounding issues then your reference point will be different all over the car.
Can you run both +ve & -ve leads of the DMM to the closest point either side of the alternator and track its actual output to eliminate grounding issues, if the voltage is stable at that point then work your way back from there looking for voltage differences each end of straps and cables rather than relying on ground points.

GlenL

Yes.

I've found grounding problems by looking at the voltage between battery ground and frame and from engine to frame. The voltage you're measuring is the drop in the ground path and it should be zero.

dr bob

I did that for a while, with test leads strung to various test points and the DMM sitting in the cabin. It's tough to safely get a connection right at the alternator B+ though. Even measuring voltage drop across the ground strap itself, battery - to chassis ground point, the voltage drop while driving was virtually none per the Fluke meter. That's why ground strap replacement was so far down on the solutions list. Meanwhile, other smarter electrical guys here were recommending the ground strap replacement. I did it even though all the diagnostics said it would make no difference, and suddenly the whole systems was good again. Symptoms I didn't even know I had were suddenly fixed.


Meanwhile, I intend to be in the CE panel area in the next week or so, to install large (60A) circuit-breaker/disconnect in the feed from the jump-post connection to the 30 bus on the CE panel. I'll look carefully at the little factory wires there, and if there's a good way to replace with new larger wires it will be done. Next part of this would then be the front of engine harness that includes the primary feed from alternator and starter terminals to the jump post. That would complete the new replacement of primary cable in the car.

traxtar928

Voltage was measured via a long cable from the post into the cabin for positive, and negative at the chassis connection behind the tool tray near the hatch lock.

traxtar928

So, with the new alternator installed, a ground strap ordered from Waytek, positive battery raw cable being shipped from GenuineDealz, and sean's engine harness, my battery charging system is getting a complete overhaul. Will report back with results. If it's not perfect, I'm going to go drive the 928 off a bridge.

traxtar928

Built 3 ground straps and covered in a very durable heat shrink that also seals the cable from oxygen. Should last a lifetime. You can see the resin that was on the inside of the tube squeeze out at the ends, making the airtight seal. These are definitely better than the stock part... heavier gauge and tinned copper.

2 are available for sale, if anyone is interested. $30 shipped to the central 48.

Petza914

Any chance this is slightly longer than the replacement cable I just bought and the same length as my original OB cable. That one would drop down and follow the contour of the spare tire well so the Sharkwoofer would sit flat, but the replacement I just got is shorter and angles through this area where I had to create an extension. If yours is the same length as my '79 OEM cable, I'll take one and can measure it tomorrow night when I'm back from Germany if you can provide the length and tell me from where to where you've taken the measurement.

Thanks.