Tracking down electrical gremlins

WankelsRevenge · 01-11-2014, 12:13 PM

Recently I've been having some issues with my battery not wanting to hold a charge. I know part of this is due to the cold weather along with not driving my car regularly. However I jump started it one day and got it running, but the next day my battery was completely dead. One clue I do have is anytime my car has power but isn't running (I have a master kill switch on my batter which I've been using to completely kill the power to my car) my turn signal arrows in my gauge cluster are lit up. I have no idea what this may be a sign of but it started doing this right at the same time I started having electrical issues. Does anyone know what may cause this or what it's a sign of?

GySgtFrank · 01-11-2014, 01:09 PM

FC electrics?

WankelsRevenge · 01-11-2014, 01:13 PM

Haha yeah. Gotta love 30 year old wiring/electronics.

GySgtFrank · 01-11-2014, 01:22 PM

I've had similar problems with dash stuff and traced it to the CPU needing re-soldered. From what I've read it's a common problem with the FC CPU. It could be so many things though that this is just a WAG.

JL1RX7 · 01-11-2014, 02:03 PM

Usually the alarm system will keep a slow draw on it. Plus some other random stuff to really make guess. I will pull the cables from the battery if I know I won't be driving it for a bit. Seems to make things play a little nicer. Sucks to reprogram the radio and the clock each time but oh well.

WankelsRevenge · 01-11-2014, 02:08 PM

Well I dont have an alarm on mine so that isnt an issue at all. Really the only thing thats making me paranoid is why my blinker lights in my gauge cluster are staying on even if the cars not running, or without the key in the ignition for that matter. But like I said I have a master kill switch for my battery inside the interior so Ive just been killing all the power when Im not running the car and that seems to be working for now.

JL1RX7 · 01-11-2014, 02:21 PM

I would find the wiring diagram for that circuit and see what could be on. Sounds like a short that is doing it. Check all your grounds since the FC never had good ones from the jump.

RETed · 01-11-2014, 04:27 PM

Electrical problems are always a PITA...
There is no way around it.
Cross your fingers you come across it sooner than later.

Basically, you need to understand the wiring diagrams (in the FSM).
Once you've got that under your belt, get a DMM that can do current draw, or Amps.

If you've got no clue where to start, I'd start under the hood...
Disconnect negative terminal from battery.
Measure current by switching DMM to current (i.e. Amps) and connect one probe to negative battery post and the other probe to the now disconnected negative battery terminal.
Normal current draw should be under 0.1A or 100mA.

Now check the the engine fuse block...
(The 80A / 100A fuse is bolted in.)
Pull the fuses one by one and measure current draw across the two points...
This should start your search.
Ignore anything lower than 0.1A (or 100mA) for now...
Find something that measures higher than that.
(Make sure nothing else is on in the car - i.e. dome light, door light, key off, etc.)
Trace the circuits one by one to see where it leads you.

-Ted

Pete_89T2 · 01-11-2014, 04:30 PM

I agree - get the FSM & wiring diagram and start tracing the circuit back from the turn signal indicator bulbs, and look for anyplace it could possibly short to, causing those lights to come on.

My best guess at this point is a bad CPU, probably a short caused by a failed solder joint. The CPU is where the electronic faggotry that causes both the turn signals and hazard flashers to flash happens... And since the hazard flashers operate with the engine off, it's a likely short circuit location. Try swapping in a known good CPU from another FC.

RETed · 01-11-2014, 05:33 PM

Or quickie troubleshooting with the "CPU"...

Unplug the unit and see if the situation changes???

-Ted

01-11-2014, 01:09 PM	#2
GySgtFrank Professional Stick Poker Join Date: Feb 2011 Location: Stafford, Ks. iTrader: (0) Posts: 1,005 Rep Power: 15	FC electrics? __________________ 1979 SA22C (parts of one anyway) http://rotarycarclub.com/rotary_foru...ad.php?t=15585 1975 MG Midget (building) http://rotarycarclub.com/rotary_foru...ad.php?t=18681 1988 N/A SE model FC, dead stock and less than 85k on the clock. This one actually runs, so I don't fuck with it.

01-11-2014, 01:22 PM	#4
GySgtFrank Professional Stick Poker Join Date: Feb 2011 Location: Stafford, Ks. iTrader: (0) Posts: 1,005 Rep Power: 15	I've had similar problems with dash stuff and traced it to the CPU needing re-soldered. From what I've read it's a common problem with the FC CPU. It could be so many things though that this is just a WAG. __________________ 1979 SA22C (parts of one anyway) http://rotarycarclub.com/rotary_foru...ad.php?t=15585 1975 MG Midget (building) http://rotarycarclub.com/rotary_foru...ad.php?t=18681 1988 N/A SE model FC, dead stock and less than 85k on the clock. This one actually runs, so I don't fuck with it.

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01-11-2014, 02:03 PM	#5
JL1RX7 Rotary Fanatic Join Date: Feb 2008 Location: Front Royal, VA iTrader: (1) Posts: 487 Rep Power: 17	Usually the alarm system will keep a slow draw on it. Plus some other random stuff to really make guess. I will pull the cables from the battery if I know I won't be driving it for a bit. Seems to make things play a little nicer. Sucks to reprogram the radio and the clock each time but oh well.

01-11-2014, 02:21 PM	#7
JL1RX7 Rotary Fanatic Join Date: Feb 2008 Location: Front Royal, VA iTrader: (1) Posts: 487 Rep Power: 17	I would find the wiring diagram for that circuit and see what could be on. Sounds like a short that is doing it. Check all your grounds since the FC never had good ones from the jump.

01-11-2014, 04:30 PM	#9
Pete_89T2 Lifetime Rotorhead Join Date: Apr 2010 Location: Elkton, MD iTrader: (1) Posts: 874 Rep Power: 15	I agree - get the FSM & wiring diagram and start tracing the circuit back from the turn signal indicator bulbs, and look for anyplace it could possibly short to, causing those lights to come on. My best guess at this point is a bad CPU, probably a short caused by a failed solder joint. The CPU is where the electronic faggotry that causes both the turn signals and hazard flashers to flash happens... And since the hazard flashers operate with the engine off, it's a likely short circuit location. Try swapping in a known good CPU from another FC.