hello friends. some of you may have seen my latest build thread in which I combined two cars into one.

part of the project was installing my 94 front harness into the 93 base model.


so i'm done now, and I have some strange issues:

1. when I plug in the CPU#2 the hazard lights start flashing.

2. the oil pressure gauge does not work - it's pegged. but when I turn the parking lights on via the headlight switch the gauge goes to zero. if I turn the lights off it drops back down.

3. the gauge cluster does not light up all the warning lights when I turn the key to ON (before turning the key over to START).

4. the BRIGHT light warning light stays lit with battery power and never turns off unless I disconnect the battery.

5. the gauge cluster does not send out the alternator "excite" signal from the CHARGE light like it's supposed to. I did a lot of troubleshooting trying to figure out why my alternator wasn't charging the battery, and this is what I finally narrowed it down to. I applied 12v to the excite pin on the alternator and it activated and started charging.

the car runs perfectly (after I get the alternator charging), but these electrical issues are driving me insane!

i'm wondering if I have left off some ground point or left some plug unplugged. #5 is the only issue that I had prior to doing all the harness/etc. swapping into my 93 roller.
I've gone through what I think is every ground wire that has to do with the cluster, and I cannot figure this out.

what did I miss? the oil pressure gauge peg/zero really makes me think i'm missing a ground wire...

 

Beuller

 

What you are describing sounds like a problem on the 12 volt side if the wiring, a ground problem. The headlight switch sends power, not ground. The dash lights receive 12v from the ignition switch, if only one switch position results in the lights working, I would look at the switch or the fuses in the system. I'll look through the factory wiring diagrams and try to get more specific info later this week.

 

the thing i found most strange is that the hazard lights come on when i plug in the CPU#2...
i see in the wiring diagram there is a CPU #2 GROUND, and i have no idea where this is.

 

After looking more closely at your description and the 1994 diagrams, I think your problem may be related to some of the wires in connector X-06 not matching up. X-06 connects the Front harness to the Instrument Panel harness. Here are some screen captures from the 1994 wiring diagram. I suspect the 1993 harness may be different, but don't have a copy to check myself.

 

thank you for the post again, scotty.

so from everything i've learned and been told, the pinout and wiring is the same between dash harnesses. i am currently leaning toward the GROUND side...

i was just looking at the diagram again and checked into the grounds again. grounds #6 appear to ground a lot of the stuff for the cluster.

i have this illustration here, but i don't know exactly where these grounds are. it's hard to make out from the pics. do you (or anyone else) have any pictures of what these grounds connect to on the body???

it looks like one is on the torque tunnel and one is on the firewall? i can't really tell.
if that's the case, i have NEITHER of these hooked up.

 

here is something interesting:
would the flasher default to FLASH and flash the hazards with ground #6 missing?

whenever i plug in the CPU#2 both turn signals start flashing...

and i wonder what happens when the ground side of the HIGH BEAM bulb is missing!

 

For a lamp to light up, it needs 12v power on one pin and ground on the other pin. If the high beam indicator lamp is always lit up, that means it is always receiving 12v and ground.

If the schematic is accurate, the high beam indicator should never light up if the ground is missing. Because you say it's lit up, I think it must have a good ground. If you have a multimeter, try measuring the resistance between any chassis bolt and the ground pin on the plug that goes into the back of the dash. I think you will find there is low resistance between the chassis and the ground pin on the plug... that's good, it means the harness ground is connected properly.

​​

 

well scotty I checked for power and ground for the areas you highlighted.

pins 4H and 4K both had low resistance to ground as you suspected.

pin 4G (brights ON from combination switch) had 12v at all times, even with the combination switch disconnected.

so something is wrong between the combination switch and the cluster, so plug X-06.

i'm currently trying to located a 1993 wiring diagram...

 

I found the 93 wiring diagram here. RotaryHeads.com - 3rd Gen RX-7 PDF Technical Manuals FD3S


the X-06 wiring appears to be the same between 93 and 94 except for the fog/Canada/stereo!

I am not really sure where to go from here.

 

X-18 appears to also be the same (93 in top of image, 94 on bottom):

 

I would try pulling fuses, starting with the 30A headlight fuse, until pin 4G no longer gets 12V when the combination switch is not in the brights on position.

 

Jacob,

That's a lot of weird stuff

It may simply be the 94 dash harness isn't compatible with the 93 main because of the passenger side airbag. That's the only difference I can think of. There's a chance the cpu#2 is also different on 94/95 cars but can't remember

I sell a lot of the CPU#2s and as I recall there is a different part # but I also don't know what I ate for dinner last night lol

 

well, according to the wiring diagram they are interchangeable! it is entirely likely I missed something, due to this being the first time I've removed/reinstalled a front harness (and dash, for that matter).

but all this stuff worked fine when I pulled it out of the 94, except the alternator charging - which I narrowed down to the cluster being bad (I still need to swap it with a known good one to verify).


this is very frustrating. not too unexpected though, as it was an ambitious project!

 

I removed the big headlamp fuse off the + battery post an the BRIGHT indicator light stayed on!

so I started removing fuses and watching the light, one by one, and the 10A ROOM fuse is what is powering the bright indicator light.

the ROOM fuse is powering both 4E and 4G.

i'm not really sure where to go now.....

 

I did some testing on the cluster just now, and each of the warning lights will light up when supplied with ground. there must be a mix-up in wiring.


I was also thinking: for the pics above I posted showing matching wire colors between years, that's only the wire colors; the routing and function of each wire could be different, but the wire color the same...

i'm losing hope.

also I assume that 1994 dash harnesses are not easy to come by. or vice versa for 1993 front harness.

 

I also just remembered that this car came with a 93 firewall harness as well, I think.

EDIT:
so I have in this car:
94 front harness (confirmed with FD15 part #)
94 dash harness (confirmed with FD15 part #)
93 firewall harness (no labels I can find)

 

update again:

I have been sick lately, but had enough energy tonight to remove the dash:

I verified all wiring harnesses are 1994:
dash harness (FD15)
front harness (FD15)
firewall harness (FD15)

does anyone know what this green connector goes to? I verified grounds #7 are connected (seen in the 2nd pic below)





I found this in a google picture that shows it, but not where it connects to:




and here's my current situation:

 

that single wire green housing plug goes to a tiny little harness that I am missing which goes up to the DOME LIGHT up the a-pillar. the other end of the harness plugs into the very top of the fuse box.

I am missing this little harness, but I don't think it's my issue.

Helpppp

 

OK, so what I would do next is find out where in the harness 4e is getting connected to 4g. Unplug the harness from the back of the dash cluster, then use your multimeter to check resistance between 4e and 4g in the harness. If the resistance is low, try disconnecting the dash harness from the front harness and see if it changes. while you are doing this, it's not a bad idea to check resistance between pins 4e - 4g on the cluster itself. It might be possible for the traces on the cluster's flexible circuit board to get shorted together.

 

update:
I've traced wiring and all wiring/pins/plugs appear to be correct. several things:
1. I traced alternator wiring from: cluster > X-18 > X-06 > X-11 > alternator
2. I traced oil pressure sensor wiring from: cluster > X-18 > X-06 > X-12 > sensor
3. I traced bright light indicator wiring from: cluster > X-06
4. I traced 10A ROOM fuse from: cluster > JB-02
5. I checked for continuity from 4E to 4G on the back of the cluster (flex circuit board), and there was no continuity -- to look for a cause of the bright lights indicator to be on constantly
5a. I checked for continuity from 4E and 4G back to their respective pins (4E > JB-02, and 4G > X-06) and also for crossing of continuity, and there was none. I think this means something internal in the cluster is lighting up the bright lights indicator.
5b. I checked voltage at X-06 (f) R/W coming in from the headlight switch, and there is zero voltage until the headlight stalk BRIGHT lights are activated, then the pin sees 12v. this is functioning as it should.
^this is leading me to believe that something inside the gauge cluster is crossing 12v between 4E and 4G and lighting up the bright light warning indicator. there isn't even voltage on the R/W wire until you make voltage go to it via combination switch.

the one thing I haven't done is swap gauge clusters to see if the actual cluster is the source of the problem!!

(link to full-size image)
https://i.imgur.com/eASvR4W.jpg

 

I swapped the cluster with a friend, and everything works correctly.


ALL THAT THINKING.

scotty, thank you for your assistance.