Mazdax605

iTrader: (5)

Hey guys,

Well yesterday I decided I was sick of looking at the wiring harness that goes to the engine on my 78 Spark yellow RX-7. I have removed the rats nest,and the Yaw carb has no wiring on it at all. I really only use maybe 8 wires in that whole engine harness,so I thought I would make my own.

Well I took the spare sub harness I took of my 79 Limited edition parts car,and started un-taping it,and removing what wasn't needed. I thought I had it all good,and installed it in the car. Well no sparks,or fires,so far so good. Fired the car up,and found that the voltage gauge/tach was remaining a tach,and was going way up as I revved the engine. I knew there was an issue,so I shut it down. By the way I am running a 2nd gen alternator,and I have modded the wiring for this a while back with the wires you will see in the pics,and a relay so the idiot lights still check when you start the car,and the tach/voltmeter still works as it should.

I spent the evening while watching the Saints game ohming out the connections to see if/where the pin out would be different. I noticed on my original sub harness that the secondary connector at the fender liner end had a large wire(to the old voltage regulator),and a smaller white with black stripe wire piggybacked to this connector. On the 79 LE harness this connector only had the large wire,and nothing else. Also the plug at the alternator has three wires on my 78 harness,and only ywo on the 79 LE plug.

On the 78 harness the white with black stripe wire at the alternator was the same wire on the piggybacked secondary plug,while on the 79 LE harness this wire(same color) was wired to the larger flat main plug at the fender area. I know I could just take this wire from the flat plug,and wore it to the secondary plug,but I don't want to hack up the factory harness from the 78,as I like to do things that are easily reversed.

In my 79 FSM wiring diagram the wiring is shown just like the 78 harness,but why would the 79 LE be different? They are technically the same year,so why the change?

You will see in pics the factory three wire alternator plug first with the far end of it next from the 78 factory harness. Next you will see the 79 modified harness with the two wire plug at the alternator end,and the flat plug end.

Any ideas as to how I can easily modify this modded harness to make it work on my car without taking apart my 78 factory harness would be appreciated.

What confuses me the most is that my 78 is an early production car,and the wiring diagram jives with the wiring in the car,but not with the other 79 car I have. I don't remember the build date on the 79 LE,but rest assured it is in 79,and not 78 like the yellow car.

DivinDriver

iTrader: (15)

It doesn't surprise me - - I have a late-series 80, and there are whole wiring systems in the car that appear nowhere on the standard A-spec 80 wiring diagram.

Example: Main harness provisions were included in the harness for power windows and power mirrors, even though those options were not available in A-spec cars in that year. J-spec builds offered them, and the same harness was used in both builds later in the 80 production run... but the US wiring diagram was never updated to reflect them.

Perhaps it was a similar deal?

rotarydude

iTrader: (2)

Ok here goes..... Mazda.... the wiring diagram where did you get if from? there are differences between the ones in the Haynes manuals and the factory ones( i like comparing all of them because some things show up that make more sense even though it is the wrong diagram). The LE wiring harness is LE specific on many parts... I don't know why totally but it is, that may be a big part of your issues I would have modded an earlier harness or one not off of an LE. I absolutely hate the external voltage regulators they cause all kinds of problems and this may be one of those cases. Are you using a electric dizzy?



The second one on the 80 harnesses as soon as mazda made the LS and Anniversary editions they started using the harness with the provisions for the extra crap. the J-spec harness is still a little different but i think that mazda really did intend to also bring power windows and a few other things with the LS or Anniversary and then backed off. Regardless I have found through the years mazda does a decent job of parts binning things (big interchangeability) they also hate to retool so they tend to use things like harnesses that are equipped to accomondate everything. This statement is really evident in the 84-5 rx7s as all cars were predrilled and tapped for any FI fittings as well as the NA stuff.

Mazdax605

iTrader: (5)

Thanks for the input guys.

Dave,

The wiring diagram I have is the Mazda Factory wiring diagram that is seperate from the regular FSM. It came with the car from the original owner when I bought it years ago.

In hindsight I should have noticed the difference in the harness,and stopped there. I did noticed the difference,but didn't think that wire was one of the one I needed,so I pressed on. I knew the LE had some differences in the wiring,but didn't think the engine harness would be different. I thought only the under dash stuff was different. Also this was the only engine harness I had handy,so I used it.

I also hate the external voltage regulator,and that is why I removed it a long time ago. I didn't want to hack up the factory harness in the car though so I left it in place,and modded it such that the warning lights,and tach/voltmeter still worked as they should. I changed out the alternator with a 2nd gen unit that had more current capacity,and was internally regulated. I am using an electronic dizzy from my old 83 LE.

Do you have an engine harness like the factory one I have that you could spare? Maybe I should just stick with the one I modded,and re-route that one wire with a barrel connector to plug it into the proper plug on my car,and everything will be fine?

I agree with you on the parts interchangability(is that a word?) of Mazda cars as I added power windows to my 83 LE,and everything was esentially there aside from a sub harness I needed for the switches. This makes sense from a manufacturing stand point. I know the engine in my 78 production car,and this later 79 LE are no different,so why the different harness? I guess this is maybe a question that only Mazda could answer,and even they may not know. Anyway I figured out the difference,but need to figure out a way to fix it.