jbpnoman

Spent 10 hours under my car yesterday getting it ready for inspection, and I can't figure out why my reverse lights aren't working. A few months ago, I finally completed a transmission overhaul. I assume my reverse lights worked before the overhaul, but I can't say for sure that they did.

After reinstalling the transmission, discovered that the plug going to the reverse sensor on the transmission magically didn't have enough wire to reach. I tugged, pulled, and traced the wire, and it isn't pinched or caught on anything, so I have no clue where the missing length of wire ran off to.

Started off by replacing both bulbs, still no light. Old and new bulbs both appear to be in perfect condition.

Decided to create my own extension harness. Easy enough, it's only two wires. Cut two pieces to the needed length, patched those wires into the sensor wire, crimped and heat shrank connections, added some shrouding to keep it all safe, and e-taped it all. Looks great, but still no reverse lights.

ALL other lights now work, including all interior lights. Is it possible that the reverse sensor was damaged in the overhaul? How can I test it? If the sensor isn't damaged, how should I go about figuring out why the lights aren't working? Worst case scenario, how can I go about wiring in a manual switch to toggle the reverse lights? I need to get the car inspected like, yesterday, and my inspector already told me that a manual switch would pass, and it would be a lot easier than sourcing a reverse switch, waiting for delivery, and installing it. In his words, "As long as the lights work, I don't give a damn how they work."

Former User

Is 7.5A dash fuse 19 blown?

If you unplug the switch and turn the key to ON(II), do either of the two terminals in the plug have voltage to body ground?

Emeraldbomber

Sounds kind of stupid but did you make sure no fuses were blown and the the bulbs arent burnt out?

jbpnoman

Fuse visually appears fine, but I know that isn't definitive. Replaced the fuse with a new one, still no lights. My Voltmeter should be returning to me within an hour so I can test them again. When you say terminals in the plug, do you mean the fuse plug, or the reverse switch plug?

edit: You said 19, and I checked 17 like an idiot. Double checking now.

edit again: Checked 19, swapped with known working, still nothing.

Swapped in a new fuse and new bulbs, still nothing.

Former User

Start here^ with the key in ON(II).

jbpnoman

Tested the reverse switch plug. On the harness side, 6V on the yellow/silver wire. On the plug side, nothing. Also went ahead and ohm tested fuse 19, as well as both reverse bulbs. All passed.

I'm starting to think the reverse sensor is dead. Unless there's something else I should test first, my next plan is to remove the sensor and see if the reverse lights come on when I press it manually.

Former User

One terminal on the harness side should have battery voltage (~12.5V).

What voltage do you read on each top test tab of fuse 19?

jbpnoman

~12.3V on the tab for fuse 19.

So the harness terminal should read ~12.5V? It's only reading 6.

Former User

Both tabs or only one?

6V is a problem.

Coupe/sedan or hatch?

jbpnoman

Only one.

Sedan.

Former User

If only one of the two fuse tabs has voltage, then the fuse is blown or bad.

jbpnoman

I tested it with the fuse removed, so I assumed only one lead should have power. Should I have tested with the fuse installed? The three fuses I've gone though passed an Ohm test while removed.

Former User

Install the fuse and measure voltage at each top test tab. What are the readings?

If both top test tabs have battery voltage, the next voltage test is done on pin 15 on the male-side of connector C131:

jbpnoman

12.3V on both tabs with the fuse installed. Sorry it took me so long to get back to this thread. Weather and work schedules have been liberally shitting on me.

Is this C131? Where exactly can I find it under the passenger side kick panel?

Former User

It's a green connector in front of the ECU. The pin and wire color pattern will match the diagram above.

The ECU is located behind the ABS control unit in the photo below.

jbpnoman

OK, I don't have ABS, but I know the connector you're talking about. I'll poke at it with a multimeter as soon as time permits.

jbpnoman

12.02V on both ends of the connector at wire. Confirmed yellow/red on one end, yellow/silver on the other. 12.11 across the battery terminal, for reference. Voltage didn't change regardless of neutral/reverse.

Where should I check next?

Former User

I assume that you back probed the wires instead of unplugging the connector.

Next step:
Reconnect the plug, turn key to ON(II), and again measure voltage at the Yel wire of the reverse light switch plug. What's the voltage?

jbpnoman

I back probed on both sides, and unplugged it. Got the same reading on all three tests, .01v tolerance.

Post #6, I mentioned I only had 6v on the yellow wire on the reverse switch. I'll go double check it now while I'm replacing my brake booster.

Former User

When C131 is unplugged, the male-side connector terminal (Yel/Red wire) should have voltage whereas the female side terminal (Yel wire) should not.

At this point, it's important to verify the original voltage test at the female side (Yel wire) of the switch connector.

jbpnoman

The male side had voltage while unplugged. I didn't test the female said - I assumed it wouldn't have voltage. I did the back-probe test while plugged in. Tested both sides to make sure there wasn't some kind of corrosion on the connector causing the problem.

Yep, going to test that now. Yellow wire, female side.

jbpnoman

11.97v at the yellow wire, female side.

Thanks for helping me work through this, RonJ. Hopefully we can get it figured out.

Former User

Plug it back in and check whether the reverse lights now work.

jbpnoman

Plugged back in, still no reverse lights.

suldy

your pin on your reverve harness might be damaged/bent. when you put the shifter into reverse, the transmission presses on a pin that sends the signal to your back lights. this could have been damaged by you/the mechanic when the transmission was off the car, laying on the ground. double check that.