SC400F4

Hey everybody,
This is my first post here, so just for some background info-I'm 20, during my high school years I was in love with Porsche 944's (owned 4 of them, never more than one at a time and all less than 3000 to buy). Since then I've broadened my horizons to motorcycles (I have a 1999 Honda F4) and I just picked up a 1992 SC400 with 159,000 miles. I got it for a relatively good price, but here's the kicker: it has a mess of electrical problems. I havent really investigated any of them because the car still runs and drives and I'm not done doing the post-used-car-purchase fluid changes and whatnot. I have a feeling the electrical mess is going to have something to do with the previous owner installing two tv's in the car, but here are the symptoms: First off, the battery dies in the car because a couple idiot lights stay on (oil, brake, etc.) as well as the digital climate control lcd. Also, the tachometer and speedometer both jump up and down when the turn signals are on, OR when i try to pretty much do anything powered in the car (such as moving the drivers seat or adjusting the steering wheel). Now sometimes these electrical gremlins will go away and the tach acts normal, but that's when the powered devices will work (the seat will actually move when I apply the button-before i would push the button, the tach would die and the seat wouldnt move).
Well, that's my story, so if anyone has any idea what this electrical mess might be let me know. I know I have to get the TV's out and start digging around (really I need to get a manual before I do any of this) but I was hoping you all might have some advice I could use.

peanuthead

sorry to hear about the problems, hope you can get some answers

sc250tt

my 92 sc400 was doing the same thing i think its a problem in the harness .i never fixed because i swapped the motor out cheack engine harness

eHIGH

944 huh? I was planning on building one I just bought, but I think imma have to let it go.

Sorry about your electrical probs. Hopefully you can get them resolved

DriftNsc3

Wow...sounds like a complete mess! I also suggest looking at the wiring harness. It may be easier to swap the engine/harness(lower miles) or just the harness. I was gonna buy a used engine for 450 in the FS section here.

Danimal

Since you have a 400, I hear a pretty normal thing to have happen is the power-steering pump can leak onto the alternator, causing all sorts of electrical problems. I know I have some slight problems with my 300 due to the ground cable running off the battery.

From what I hear most people have at least *some success after cleaning their grounds off, and some with changing out for a new battery. Your problems sound somewhat different that anything else I've heard about, so it may not be anything like what I suggest, but it wouldn't be a bad place to start.

Happy SC'ing!

-Dan

SC400F4

Thanks for all the advice, i'll let you all know what i find

SC400F4

Thanks for all the advice, i'll let you all know what i find

aliga

iTrader: (147)

change the radio harness.

sean9975

do u think that will help him. oh because of the previous install? i have a simular problem, my gauges aren't buggin but one of my turn signals in my old tails melted some wires and caused a split second fire in my inside fuse box. now my corners dont work. so how hard is it to change the harrness. i know the radio harness isnt that bad once the center console is out. but how is it to change the inside fuse box? or do i 2 have to change out my harness? and i heard about the grounds, how many are there and where are they? sorry sc400f4, figure i jump on and get some answers as well. keep us posted on your results

sc400a1

check your grounds it sounds like your power is backfeeding through the instrument cluster i have a safe bet that your seat power shares a common ground with another one of those problems you listed above find the ground clean it and put it back in also it sounds like your signal multifunction switch has a stuck contact remeber that the v ref on the cluster lights is low so it wont take much of a backfeed to light them up

IronCobra

Definatly check to see if the PSP is leaking into the Alt.

Here is another idea,

Completely removed the wiring mess that the previous owner installed. He may have tapped into wiring rather than doing it the correct way. He could have caused some errors in the ECU.

Undo everything you can see. Remove the bottom dash panel above your knees and see what all as been tapped into. You might have to remove the radio as he could have tapped in behind there. It sounds like he is pulling leads from the climate harness causing the lights to stay on. He also may have used a Test light instead of a multimeter to check leads. This could have caused damage to chips and factory parts.

Unplug and disconnect ANYTHING that looks aftermarket. Once you have done this, rewire everything correctly. If you do not know how then DON'T TRY. Take it to a shop that has lots of 12vt experience.

I'm sure the previous owner ran all the main power leads to the harness and not the battery.

The correct way to avoid the problems your having is to have ALL main power leads ran directly to a fuse battery connection going STRAIT to the battery. Then you should run your "switched" power leads to the main ignition harness and fuse them all with 15amp fuses.

I'm sure the repair is simple. But you may have to do some intense leg work to get everything back to stock.

Good luck! Lots of good information here and lots of great people to help you out!

LXotic

well good luck fixing up the car.
I suggest changing some wiring harnesses....

sc1jzgte

my roomates 240sx wouldnt turn off, you guys may remeber my thread, there was so much modification to the wiring we spent hours rechecking our work, and days messing with crap, finally got a professional electrician to check it out and it took him like 30 min to fix it. Ill tell you our fix but my suggestion is dont waste all your time and have an expert do it, weve done swaps and custom wiring but Im no expert. basically it was a short somewhere and he took the key out and started hitting all the switches and crap, when he hit the cruise control button the car shut off, then he unplugged the cruise control switch and the problem was gone(we diddnt have cruise control in the sr20 working anyways) hope that helps

aaronjz

had a problem in my sc not turning off before. but after everything. it ended up being a shorting starter . that was it for me. i suggest just getting it diagnosed