Electrical Troubleshooting
 

Hey guys, so yesterday my 04 MT wouldn't crank. At all. Turning the key in the ignition just gives me a slight click sound in my fuse box area, the starter does absolutely nothing. Since then, I've done a BUNCH of youtube research, and w/ a voltmeter been narrowing stuff down. Specifically I tested the pins on my starter relay in my fuse box (Technically PDC right?). I'm attaching the electrical diagram so I can refer to it. Before this I had next to no knowledge in car wiring, but I do have a chemical engineering degree and an pretty good at physics/circuits. Plus a decent amount of free time.

I tested the relay itself, giving it power causes it to click (switch closed), and I'm measuring resistance between the load side prongs. So running a jumper wire from L/R Pin straight to the battery cranks my car. It starts up fine, its essentially like wiring my battery straight to my starter solenoid, so that pin should be good. I also accidentally "started" it trying to get the relay out, I squeezed the side too hard, I guess I closed the switch, and my starter revved up. These both eliminate starter problems in my mind.

I also tested the far right pin (R), getting a constant 12.x volts, so the connection between that and the battery is fine (makes sense since squeezing the switch shut connected the current). This is important, since my negative terminal on my battery isn't suuuper tight. But this would prove its getting enough juice, correct? (Plus the squeeze test).

Now testing the top (PCM side) gave me no current. However, I did this before I had done too much research (just watched some guy on youtube do it), and it makes way more sense to me that this should be a ground. I'm going to retry this connecting one side of my voltmeter to battery positive, and one side to this pin. Switching this up, I got like 11.5 ish volts with the key on "on", then 12.x with the key on start. So I think my PCM is working/grounding this correctly.

Either way, the bottom pin is from my ignition switch and my starter interlock switch. And this one is getting no power when cranking, which I believe is the problem. So following the wiring diagram, I tested the 15A Ig Key fuse, its fine. I tested what I am 95% sure is my ignition switch wires (6 wires, should be pictures 1 and 2). Two of them were constantly on (assuming battery source).
*Question 1: This is essentially the input of the circuit right? Like current goes in here, then key positions complete different circuits and the output is from the same connector?*
The other 4 turned on at diffferent key positions (acc, on, start). All of them seemed to be responding "normally", including one that only reads voltage (12.x) when my car is cranking. I put in clutch for this, but I don't think this matters, as that check is farther "Down the line". This should be the output in my electrical diagram.

However, the next component is my starter interlock switch, which the internet has told me is basically my clutch switch, that completes a circuit whenever the clutch is depressed. I think this is picture 4? I've tried back probing both of the wires going into what I believe is this switch (sitting high up on my clutch pedal itself, see picture 5). And I'm getting no voltage whatsoever in either of them. This implies that there is a break somewhere between my ignition switch and my starter interlock switch, correct?

So going on that assumption, there are two things I want to know.
First of all, how do I remove the switch itself, or at least disconnect the wires? I can't seem to find a way to remove the plug. Do I flip out that metal bar (blue arrow pic 5)? Is there a tab on the top, out of view? If I remove this, I can probe (not backprobe) and one of them should light up as my car is in crank position correct? Even with the clutch not depressed?)
Second of all, If the issue is in the wire itself (what I'm assuming is the issue), it seems to go into a wire bundle (picture 3), then I think through my firewall and back? Troubling, I don't think the colors match up. Its really hard to see colors in this, but I'm pretty sure my ignition "start" wire is white (maybe its dark blue). Either way, the interlock wires are black and purple. Is this a normal thing? Or was my wire maybe spliced or something before I owned the car.

If this is the case, I feel like the simplest solution is to just cut the wire, and redo the circuit outside of the wire harness. If not, this seems like an uber pain the ass to check the wire along the entire length (but I would assume its super odd to fail along the middle somewhere right?).
https://cimg1.ibsrv.net/gimg/www.rx8...1f61f11ae1.png
Top down view of what I back-probed for ignition switch.
https://cimg7.ibsrv.net/gimg/www.rx8...e1ee1d580f.png
Better, underneath view of ignition switch wiring.
https://cimg6.ibsrv.net/gimg/www.rx8...7b4ae6dd50.png
Where these wires lead to, seems to head past the firewall then back in?
https://cimg9.ibsrv.net/gimg/www.rx8...e50da79083.png
Location of starter interlock switch?
https://cimg4.ibsrv.net/gimg/www.rx8...138d72ffda.png
Wires I probed that are receiving no current.
https://cimg7.ibsrv.net/gimg/www.rx8...54f88e35ba.png

Have you tested the starter itself? Its just 3 bolts and you can test it on a workbench or take it to Autozone or something just to rule it out.

I'm not sure I "officially tested" the starter, but I was able to start the car just by putting the key in the "on" position, and linking my battery to the "starter pin" of the relay. Basically just sent battery power to the starter, and it started fine. Drove it around for 20 minutes or so as well (not that that has to deal with the starter).

"This is important, since my negative terminal on my battery isn't suuuper tight."


?? If your saying that your neg batt terminal isn't tight then that could be a problem. Or did I miss somthing ?

Well if that’s the case and you are sure you’ve found the faulty wire, go ahead and route it on the outside of the harness to the starter if you suspect a break in the wiring that’s hidden just to see if that works. I’m not sure what color that wire is unfortunately, nor do I know how to remove that clip without causing damage so this is the route I would go because you seem to have already narrowed it down.

Yeah I understand how that generally can be an issue. Couple things

1. I have been driving it for months with a "loose" negative terminal, it has been starting fine.
2. I am still reading 12+ volts going into my relay and throughout my entire system.
3. All electronics are working, headlights are still bright
4. I "started" the engine by manually squeezing the starter relay in my fuse box (was actually an accident, but it proves that the starter is getting enough juice, the relay just isn't closing to complete the circuit).

I guess its possible its the negative terminal, but I think its unlikely knowing the above.

https://cimg6.ibsrv.net/gimg/www.rx8...b87a8fdd6f.jpg
One switch is a twist .grab the whole thing and turn counter clock wise
https://cimg6.ibsrv.net/gimg/www.rx8...6b20019256.jpg
The other has a black tab on the bottom. Pull it out and push up on the switch .

this help at all

@Red line envy
The pictures help immensely, thank you.
So I would twist it off first and both sections would come off my clutch pedal, correct? Then I get to the tab and disconnect the wiring afterwards?

Yup easy peasy.
Good luck :fingersx:

Voltage is meaningless. Current is what gives your starter enough oomph to turn the engine over. Poor connection doesn't change the voltage, but it sure as hell changes current carrying capacity.
The fact that the starter spun up while not pulling the engine with it is also not an indicator. That doesn't require a lot of current.
All the other electronics do not require nearly the current your starter does.
You've also been driving with everything else on the car the way it is, and it started fine.

Tighten that battery terminal and clean it up if necessary before you invest a bunch of time in redoing your wiring. If I'm wrong, you lose 2 minutes doing that, if I'm right you save a whole bunch of time redoing wiring only to discover that wasn't the problem.

Do you have an immobilizer light on the dash illuminated?

Your symptoms could also be caused by a problem with the immobilizer

Tightened up the terminal, no difference, I also put one of those battery recharge/engine assist jumper things on the clamps, and still the exact same thing (I'm under the impression that couldn't solo-crank my car, but it didn't even seem to attempt to turn it over, and it didn't engage my starter relay [no click]).

The immobilizer light (car w/ a key inside it) disappears in a second or two once I rotate my key to the "on" position.

Only thing I can think is it actually is a wiring problem. Did you try to route that cable to see if the starter would crank? I've never personally experienced a problem where I actually had to rewire anything in any of my RX8's and I have had some electrical problems as well. Usually most problems are fixed without having to mess with the wiring harnesses.

Also, new update. I have taken off my clutch interlock switch, and been probing/backprobing the wire connector going to it. I get voltage (still not measuring current, sorry Loki) on one of the wires. HOWEVER, only when my clutch switch plunger thing is depressed (normal resting position), and when my key is in the "on" position. I read voltage without the key being cranked. Does this mean this is actually my output wire? If so, this means that there is some type of disconnect between the ignition switch and clutch switch, right? I can not get any readings on the other wire no matter what I do. When I short it, and directly connect the pins (with the clutch switch unattached), I lose all readings for both wires. I'm not sure what would be causing this? Any ideas?

EDIT: Also my "start" ignition switch wire is blue/white, while my two wires going into my clutch interlock switch are purple, and black. So I still have no idea how to figure out which one is the input or which one I should replace if that is the issue.

Not quite sure what you mean, but I have physically matched the load contacts on the relay and the starter/car cranks. Furthermore, I have directly connected a wire from my battery to my "starter pin" (L/R) on my electrical diagram, and the starter cranks fine. It seems the issue is on the non-load side.

Bumping this a little bit, as I have a question and don't want to make a new thread.

After completely bypassing my clutch switch with a piece of wire, I am still getting no readings on my relay side, meaning there is some sort of issue between the clutch switch and the relay. My question is: I need to be 100% sure that my clutch switch (thing with 2 wires and a plunger above my clutch, pictured above) is the "starter interlock switch" on my wiring diagram. I ask this because either my wiring for it is not stock, or, I am looking at the wrong thing. (Wires should be white w/ blue stripe going in, light green w/ red stripe going out, whereas I have purple and black and a slightly smaller gauge (at least it looks that way). It doesn't make sense to me that these should be different unless my wiring is running into something else as well, which is not depicted on the diagram.

My next fix is attempting to run a new wire through my firewall to my relay directly from the clutch switch, is there an easy way to do this without removing actual ass-loads of stuff? Is there some other hole I can run this through that is easier? I don't really care if its pretty, but I'd like to avoid drilling one.

So quick update, after messing around with the wiring, and basically routing one through my door into my hood, I realized that the switch in the pictures is not my starter interlock switch. Apparently this car (and others as well) have two clutch switches, one is generally for cruise control (front one), the other is your starter switch. These wires match up, everything is now working fine. So problem solved, and I'm attaching a pretty bad picture just in case anybody else is as dumb as I am. Red is what I wrongly assumed was the SIS, Yellow is what I now know to be correct. (circle isn't great, its the black and white piece, not the metal protrusions).
https://cimg2.ibsrv.net/gimg/www.rx8...af6a57c7c9.png