S13 RB20DET RPM Counter Fix (Pin 7 ECU > Pin 19 Cluster)

[silverzx]

Hey guys,

Having some issues with getting the RPM counter working on my S13 which has been converted from a CA18DET to a RB20DET. The speedo works along with everything else, just not the RPM.

The problem is the RPM gauge doesn't work, from what I understand RPM is pin 7 on the RB20DET ECU which is red/yellow. I haven't traced the wire the whole way but I believe it's supposed to go to pin 19 on the cluster plug which seems to of been cut and a longer peice of wire soldered on - which goes no where and I assume went to an aftermarket RPM counter once upon a time. I've tried to bridge the connection and still get absolutely nothing.

Can anyone guide me on what to do next? Obviously I could trace the wire back from the cluster to the ECU but that means unwrapping a load of loom behind the dash which really I'd like to avoid. I could get a temporary piece of cable to run directly from the ECU to the pin 19 on the cluster plug, however I'm fairly certain the existing wire thats been cut (and I bridged) isn't the problem here.

I've seen a few people posting about putting a 10k OHM resistor on the back of the cluster on DriftWorks and other various forums including here but really wanted to see if anyone had first hand experience and could advise what to try next.
https://www.sxoc.com/vbb/showthread....speedo-working

The ECU Octopus Wiring (showing pin 7 red/yellow RPM)


The correct ECU diagram (to my knowledge).


The cluster plug showing pin 19 cut and soldered to a longer piece of wire that goes no where, I bridged these, made no difference.


The other cluster plug that's irrelevant.


The current situation.


Someone else posting about a similar problem on DW but from CA>SR.


Cheers everyone!

[speedingmofa]

Don't rely on wire colors.. Use a multimeter, find the pin on the ecu, and find the one on the connector.
The cluster only needs 12v and the TAM signal. The signal may be off, but you can adjust it, there's an adjustment screw if you pull out the rev counter

Also check if your ecu has any damage inside (it will smell horrible). I toasted the transistor to the ecu tach output once... blew it right out due to a short, the ecu smelled like burnt electronics/chemical

[silverzx]

I can confirm fitting a 10K ohm resistor on the back of the counter has brought it back to life. Hopefully that'll help someone else one day!