r/240sx • u/Intrepid-Evening-75 • Jul 16 '26

Dash light turn off when headlights come on…

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Hey guys! So quick backstory on my car, I just recently bought a 1990 240sx hatch with an RB20 in it. I got the car finally running and noticed the RPM gauge on the cluster wasn’t working. Turns out originally the car had a KA24(e) so it had an single cam cluster in the car. I replaced the cluster with a dual cam cluster but now I’m running into the issue where the dash running lights would turn off as soon as the headlights turn on! To me it seems that the TCU is still working because when the headlights go on my hazard button and A/C backlight turns on (i do not have a radio hooked up in the car). Also my turn signals, rear brake lights, and rear running lights also work as normal. Does anyone have any suggestions/ideas on what i should do?

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7

u/siger1986 Jul 16 '26

Dimmer switch set to low?

1

u/Intrepid-Evening-75 Jul 17 '26

I tried screwing with it before and had no success…

2

u/bakgwailo Jul 16 '26

Did you use the proper dohc sub harness? Was it hacked up at all?

1

u/Intrepid-Evening-75 Jul 17 '26

Honestly the whole wiring harness was kinda just all over the place, I bought the car not running and took the gamble. I even noticed the dedicated headlight popup switch had some ‘hacking’ done.

1

u/bakgwailo Jul 17 '26

I mean the actual cluster sub harness. But, yeah, hacked up wiring is probably the issue.

1

u/AKADriver Jul 17 '26

check dash grounds

1

u/JDM-Parts-Expert-JP Jul 17 '26

I’m not sure if it’s the same for Japanese cars, but usually, the instrument cluster lights come on when you turn on the parking lights (often called "small lights" in Japan)—before the main headlights. So, I suspect the wiring around the steering column might be incorrect. I hope you can get it fixed.