Neep

The Question:

My Main fusible link keeps blowing out on me, where should I start looking for the reason for this? Also, what is the correct battery orientation? (Wire closer to the driver is _______ Wire closer to the headlights is ______ )

The Very Important Background:

I was having a very bad day. I couldn't get my motorcycle to start, I blew the electrical in my truck, so I pulled my RX-7 off the trailer to drive home.

Already I was having issues with my leading spark not firing for the forward rotor. I hadn't gotten around to fixing it (or even finding out the exact source of the problem) but I needed something to drive. My little seven (it's an 85, with the 12A motor, no power windows or rear wiper, but it has the sun roof and the Equalizer with the stereo) had also been having issues starting sometimes, not often but I'd turn the key and all power would cut out. I could try a few times or wait it out, and the seven would start up.

That day I looked under the hood and saw the huge amount of corrosion on my battery terminals and realized "Hey, maybe that's the problem!" I set out on my way home resolving to fix the problem "Eventually" because well... it's starting to rain. Off I go and the seven begins to die on me. It's like the car can't pull enough juice from the battery to run everything, if I turn on my headlights, the car starts to stutter and the tach starts to fly all over the place (Mind you the revs don't fly at the same level as the tach, at least they didn't sound it) If I shut off the headlights, the car goes back to normal (as normal it is with a non firing rotor) so I creep my way just before dusk in the rain to my local AutoZone. I figured I could buy me a new battery and have them check my alternator to see if it's charging.

After asking if the guy behind the counter can check if my alternator is charging and he says essentially "Dude, I don't want to get electrocuted" (A valid point in the rain... I guess... :P ) I buy a new battery just to get me home. Drop it in where my old one was and start tightening it up... and the faqers sparking on me.

This is where my frustration took hold and instead of following reason I followed the example of my father which is "If it don't fit... FORCE IT!" so I just kept tightening the cables down. Maybe it's the wet cables from the rain and we're just arcing over the wetness it seems to be arcing more vigorously and... WHEEE!!! Three wires turn red and all the electrical in the car dies. I didn't know this at the time, but the three wires that turned red were the fusible links. So I look a little closer at the battery I got and CRAPPLES... looks like the battery had reversed terminals from the one I just traded in. Well with the car dead I return the battery, get back my old battery, dump it in the passenger seat and mothball the car for the next year...

Well I've been missing my little seven so I decided I'd try and get it up and running recently. I buy my new fusible links (and learned that only the main center one was blown) plug them in, charge up the battery and go to drop it in the engine compartment... shittles I have no idea what the correct orientation is for my battery. I try and trace the wires but lose track of them once they get deep in the engine compartment. I pull out my Mazda shop manual, and check the wiring diagrams... Well I can't figure out the orientation from the battery here, then I find the drafted pictures of the wiring with cutouts of the car... ok, maybe I can use this to trace to ground... ok I think I got it.

I plug the battery in the way I thought it went (Two terminals closest to the driver’s side) and it starts sparking... ok, let’s try the other way... and it still sparks... ok, let’s go back to the first way and... look at that fusible link melt.

Well now I need some direction. I think I got the battery orientation right, but I’m not certain, so which cable is positive and which is negative (One closest to the driver is _____ One closest to the headlights is ____)

However if I did have my polarity right, where do I start tracking down a short like this? I’d love to have my little seven up and running again, but if I can’t figure this out, she’s probably not destined for the good life, because I don’t have the available capital to see her fixed by a professional.

lfd75

Wire closest to the driver's is negative, closest to the headlight is positive, also the positive terminal has the wire going to the fusible links and the negative just goes to ground. Electricity is not my forte but if you're blowing the fusible links without turning the ignition on I'd start by looking there.

Vashner

Aye start with the main battery cables. They can go bad internally to where it looks ok but is all green corrosion inside.

Remember - remove neg then pos / install pos then neg.

Neep

Thanks for the responses... it may be that I installed the battery backwards again... I think I had positive going to the lead closest to the driver. I'll try it again on monday (soonest I'll be near the seven) and see what's up.

Thanks!

Neep

Well I tried again, making sure I had the battery hooked up right and the fuse blew again.

So I guess it's a short some where in the system (Hopefully an easy fix... hopefully?") Is my best bet just to check methodolically starting from the fusable link down looking for low resistance in the system and hope for the best.

Are the two other fusable links on totaly seperate circuits so I can discount any problems stemming from those circuits?

The only way I can think of not to get virtualy no resistance at every test point is to disconect each component and check it isolated from the circuit... is this correct, should I be disconnecting certain different sub circuits from the overal circuit and testing them individualy. I've never had to lok for the failure in Automotive wiring. I know this isn't going to be fun, so any information on how to proceed would be great.

gsl-se addict

iTrader: (3)

Okay. First off, the negative is closest to the headlight. It should be a black cable w/ a yellow stripe. The positive is just solid black and has a second smaller wire attached to it (this feeds the fusible links).

The main fusible link is the center one. The other 2 are for the headlights and the headlight retractors. You can pull these two links out to help isolate things. I can tell you that since the fusible link(s) are blowing, the short is in the engine bay (or battery is backwards). First get the battery installed correctly. You could try to remove the alternator output wire (large wire). Make sure it doesn't short out against anything. Installing the battery backwards can kill the diodes in the alt and make a short..so your prob might be there.

Power goes from the battery (+) to the fusible links. The main link then carries the power to the fuse box inside the car and also connects to the alt output wire. If the main link is blowing and the battery is installed correctly, the problem has to be the alt, wiring to the alt, or the wiring from the fusible links to the fuse box in the car. The only other possiblity is if someone tapped into a constant power wire that feeds the fuse box (say for an aftermarket deck), left it unfused, and it is shorting out.

I would say if the battery is installed correctly, then the problem is most likely with the alt (or wiring to the alt).

Neep

Awesome, thanks for the detailed reply. It's great to be able to isolate it to one of two main culprits, the alternator or the wiring to the fuse box. It's not great that I probably messed up my alternator, but finding the problem is the first step on the road to repair.

If it is the alternator is it possible to economicaly rebuild it? If it's not I may end up refreshing my memory on an alternator upgrade I saw on here beforee. I like my lights bright, and an upgraded alternator gave me the impression of brighter lights....

I guess breaking a part is the best time to update a part :P

Again, thanks for the response!

gsl-se addict

iTrader: (3)

You can take it to an alt/starter shop for a rebuild. As for cost, it depends on what it needs. I had an alt with a bad voltage regulator, and it cost about $70 to fix/rebuild.

I would recommend getting a good used alt. You can pickup a stocker or even an upgraded alt for $30 or so. I'm a big fan of the S5 alts ('89-'91, 2nd gen RX-7s). It goes in with only a simple wiring change needed and has an 80A capacity instead of the 55A the you currently have. I'm running the S5 alt in my GSL-SE, and I love it. Everything just works a little better (wipers, blower, etc.). Voltage holds steady even with all that stuff going. There is a write-up in the archives on the S5 alt upgrade. If you have an questions about it, just shoot me a pm.

G/L on tracking down and fixing the problem.