Revers Light Troubleshooting

[VR4EVER]

I have a 2013 FRS that I did an LS swap on 2.5 years ago. Car runs and drives perfectly, everything works as it should... except my reverse lights. I bought the chassis from a guy that had done a BEAMS swap way back in the day, and I bought the LS swap stuff from a guy that has previously swapped his FRS (so it was pretty much plug and play for me). I am using the AGT translator for my canbus signals.

I would like some input on troubleshooting, and I have already checked the bulbs and fuses... please don't point those out. My understanding on how the system works is below, can someone confirm or deny if I'm way off base? I have all the wiring diagrams and at this point I am trying to narrow down my wild goose chase on a broken wire I think...

- Ignition on -> 12v signal to the transmission switch
- Transmission switch closes (you put it in reverse) -> send a 5-20mA signal to ECU
- ECU then says 'oh, you're in reverse, let me turn on lights' and sends a signal to the fuse box at driver kick panel
- lights get power from fuse box

Things I think I know (have to confirm due to chassis history and I didn't do initial wiring):
- My wiring looks good at the big engine/chassis plug, I've quadruple checked and tested continuity, all seems good
- Confirmed transmission switch closes when in reverse
- At no point during any testing have I gotten power back to the lights, this includes me sending 12V direct through the grey plug (that typically sits at back of FA20 engine beside the red plug). I really expected the lights to come on doing this.

I know I'm missing something, and it's probably very obvious. Does anyone have any ideas? I haven't done my testing with the engine running, just with the key turned all the way ie power on.

[VR4EVER]

I doubt I'll get many responses on this thread but wanted to add more troubleshooting.

This morning I jumpered plug A59 (the grey plug that's on the backside of the FA20/top of trans) and the reverse lights came on with ignition. So the front half of the system and back half of the system seem to be working correctly and the ECU is in the middle. Am I missing something here?

[EndlessAzure]

Fuse?

[VR4EVER]

Originally Posted by EndlessAzure

Fuse?

You didn't read any of it did you?

[Grady]

I would check the fuse.

Do you have a 13 Wire diagram? I know on the later ones the system is a lot simpler. Fuse to transmission switch to lights. The neutral and reverse will feed the ECU but that is just for info. As with any electrical troubleshooting you just have to start checking to see where you are losing power or ground.

[bigB]

If you disconnected the connector at the transmission, shorted it out, and the lights came on, it can only be one of two things. Either the switch in the transmission is bad, or you aren't getting the connector on all the way. When I r&r’d my tranny, I didn’t get the connector back together correctly the first time. You can check the tranny switch by disconnecting the connector and measuring the resistance of the switch. Not in reverse, very high (I would guess over 100k ohms). Put it in reverse, it should be very low, 1 ohm or less I would guess. You can do this with no electrical power on the car.

[VR4EVER]

Thanks for feedback, I didn’t measure ohms on the switch, just used the buzzer noise function to test for continuity. I’ll make sure it’s actually bad. I’ll also confirm that the connector is making correct contact. I initially made this to figure out what was needed to test the back half of the system from that grey switch. Surprisingly someone on Facebook helped!

[speedy racer]

Hey I have got the same problem, my light was erratic like the switch was the issue.