jackhild59

iTrader: (7)

I have a voltage drop between my underhood and interior power systems. Here is what is going on:

At idle 850 rpm I have 14.02 volts at the battery, alternator B, main fuse, all underhood fuses. This is at idle with nothing on OR with lights, cooling fan, A/C clutch, interior fan basically *EVERYTHING* running. 130 Amp Alternator Sweetness! Quite satisfying is the BAC is working correctly to bump RPM when A/C engages.

All the idiot lights work, including the charge light.

I have a chinzy digital voltage meter that plugs into the lighter. The lighter works fine and will heat the cigarette lighter cherry red. When idling the gauge shows 13.8V. OK, so I put that down to $4.99 shipped from China-maybe they didn't calibrate it correctly?

When I turn the A/C on low speed the voltage drops at the China Meter to 12.5V. Volts stay at 14.02V underhood. Turning on A/C adds the A/C compressor clutch load- E-fan load-, cooling fan (oem) load and a little interior fan load.

Increase the interior fan to high and the China Meter drops to 12.0V. Turn on headlights, China meter volts drop to 11.8V

What I cannot figure out is why the cigarette lighter voltage drops as I add incremental loads, while the battery (and main fuse box) voltage stays stable.

I have not plugged in a standard plug and measured the voltage with my meter; I suspect that it would confirm the voltage drops as I add load.

Suggestions where to start looking?

Thanks in advance.

-Jack

DaBrkddy

Most of the interior accessories draw power from the interior fuse panel. The wiring between this fuse panel and the alternator/battery is probably not in good condition.

FourFiveFive

Check your grounds man. If you are getting a drop from engine bay to interior, throw a beefy ground from your dash bar right to the firewall. Check your chassis ground from your battery as well. A weak/corroded/loose ground will cause all kinds of issues, both inside and outside of your engine bay. A good reground kit can give you up to a couple volts of charge (depending on your system and accessories). Rotary resurrection has a great ground writeup you might wanna check out.


Rotary Resurrection home of the budget rebuild.

jackhild59

iTrader: (7)

Is there a main ground under dash, or are there several?

Does anyone know where the main ground or grounds under the dash are located?

satch

iTrader: (1)

There's a plug with a handful of grounds near or against the fire wall near the steering column I believe. I know Styx knows exactly where it's located.

jackhild59

iTrader: (7)

under the dash inside the cabin?

satch

iTrader: (1)

In looking at the wiring diagram (last page of document) it indicates the ground wire for the lighter is found at JC-03 which appears to be behind the center console towards the front of it. If need be you could aways add an additional ground if you think it would rectify your problem. There's a bolt which fastens the console to the body right at the end and side of the console (hidden behind the carpet). That would make a good grounding point.

clokker

iTrader: (2)

IIRC, there is a multiwire ground point on the steering column bracket, near the firewall.
It's possible it can be seen when the gauge cluster is removed.

jackhild59

iTrader: (7)

Thanks for that direction, Satch.

I have measured 27 ohms from the body (shock bolt) to the battery neg post. I've measured 220 ohms from the alternator body (or grounding bolt or upper intake manifold ) to the battery neg post.

I've decided to rework all the factory grounds on this car, including the ground wires to the ECU. All the weird electrical things going on, little and big have got to be related to grounds. I have a buddy who is in the Porsche 928 business. He tells me that the 928 platform is similarly plagued by grounding issues. He recommended using Deoxit spray on the fuse boxes after removing all fuses. Advised to either clean the old fuses with Deoxit or replace them with new fuses.

Additionally he told me that the main connector, FR03 on the diagram, between the front harness and the rear harness will be corroded. Again, Deoxit.

jackhild59

iTrader: (7)

According to the wiring diagram, that would be JC03?

thanks!

satch

iTrader: (1)

JC-02 steering wheel

JC-03 console

jackhild59

iTrader: (7)

Is JC-01 the multiple connector on the shock tower, driver side, below the Trailing Coil?

Not the battery ground.

satch

iTrader: (1)

Yes.

jackhild59

iTrader: (7)

Interim update:

I waited to do the grounding clean-up for my Deoxit to arrive.

Today I cleaned the main harness ground (inside the shock tower). I used the Deoxit, I chased the threads with a 6mm tap. I used the Deoxit on the threads, the tap, the connector. I lubed it all up with dielectric grease.

I did the same for JC-01 on the back of the shock tower. I used the Deoxit on the connector and the tabs, cleaned tapped and lubed it up.

Volts at the battery are now 14.5 at 1000 and 14.4 at 800. Headlights, defroster, cooling fan on etc. No heater blower.

For the first time, the lighter agrees with the voltmeter test at the battery-UNTIL I turn on the heater blower. Then, as before, the volts collapse.

I'm on the right track. JC-02 and JC-03 are next.

Then the ECU, Engine, boost sensor and bellhousing grounds.

Stand-by.

jackhild59

iTrader: (7)

clokker is right. Again.
JC-02 painintheass location:



JC-02 is behind the Dash Cluster





Closer view

RotaryEvolution

iTrader: (30)

you should also clean FE-01(single ~10gauge wire connector Black->Black) just below the engine fuse block and the ring terminals on the fuse block itself.

JerryLH3

iTrader: (11)

Hmmm, as I look toward the garage at my car in a million pieces, I think to myself "This may be useful to do now."

jackhild59

iTrader: (7)

Yes!

jackhild59

iTrader: (7)

Does anyone have some guidance to finding the JC-03 ground? I have the radio out, the logicon loose and pulled out, the radio surround and vents off.

I'm trying to not break anything, so looking for some guidance here.

Thanks

Jack

PS: I found that the radio wires/plugs were cut off by a previous owner.

jjwalker

Woah, hold up!

Your subdash plastic is BLACK! Mine is peanut brittle colored and well....brittle.

RotaryEvolution

iTrader: (30)

black or peanut, they're both made of butter


i had an excellent condition S5 black dash(yellow plastic) i bought like 8 years ago, stored indoors, it's now more broken than the one that is in my car(gray with black plastic base)... even bubbled up over the cluster and it hasn't seen the sun in a decade.

JerryLH3

iTrader: (11)

Weren't S4 dashes black plastic and S5 dashes beige/peanut/whatever? Based on my recollection of cars I've owned/worked on, plus what I've seen in the junkyard, I think that is the defining line.

jackhild59

iTrader: (7)

My under dash plastics in S5 Vert is PB colored and fragile. It is pockmarked with the grey stains of JB @eld on nearly every anchor point that I have accessed.

My S5 dash had dash-zits over the gauges when I purchased it 10 years ago. I was disappointed to find that they are beginning to erupt in the rest of the surface this summer. I need some RX-Clearasil!

All three S4's (all 1988 models) I've touched are black underneath. None have been as breakable as the S5. I have no JB Weld spots. Yet.

And does anyone have experience to guide me to JC-03 ground point?

RotaryEvolution

iTrader: (30)

no idea where that one is, only had a dash out once and it was a stripped down car when it came to me.

satch

iTrader: (1)

You can tap into the ground for the lighter and ground the other end to one of the mounting bolts for the center console. The console bolts to the body on each side of it at the very bottom of the console (bolts are hidden a bit just under the carpet).