Let me preface this by saying the positive ground electrical system is not my specialty. I’m learning as I go, so if this is a “duh” answer, my apologies in advance.

In short, I’ve installed an aftermarket backup camera. (Pictures and a write up to follow) Everything works, except I cannot figure out what to trigger this thing off of when the car is placed in reverse. (Currently I’m just using a manual switch)

I took my multimeter and started with some basic logic to find the wire responsible for sending power (or grounding) to a reverse light. In park, I checked the output of each pin on the connector harness on the rear bulb assembly. I grounded my meter to the battery and found two pins with 12 volts (orange color wire I believe) and one pin with 5 volts.

With the engine off, key in the on position and parking brake on for safety, I placed the trans in reverse and tested again. Confusingly, the only difference I found was the 5 volt pin was now putting out no voltage. The other two pins remained at 12 volts. I repeated the test on the opposite side and found the same result.

I read in another post that you can use the Black/Green wire on the driver side. Apparently this wire provides power to the backup sensors, turning that module on when in reverse. But with my testing not adding up, I stopped out of caution.

Before I start trigger happy t-tapping into cables trying to figure this out, I wanted to ask you fine folks. Am I doing something wrong here or is using the reverse light to trigger a camera just not possible? If that’s the case, any ideas on something else I could use?

 

It is a switched negative that powers the reverse lamps. The positive is always live.

(The car body is also always negative so it is not a positive ground car.)

So what you need is a way to turn this switched negative into a switched positive.

You may be able to use a relay, but make sure it is a low current one and that the 12v is fused, just in case.

Mellow

 

The Electrical Guide shows how it is arranged JagRepair.com - Jaguar Repair Information Resource

 

Ok, an update. Almost there.

I've tapped into the feed wire going to the reverse light and wired it to the camera trigger wire. As noted above, due to the positive ground, this feed is always hot unless the car is put into reverse.

In short, the camera is always on unless the car is in reverse.

So in layman terms, what relay could I try that would send a positive 12 volt feed out when the typically on 12 volt input is removed?

(I think you guys are going to like this when it's done...it has one slick party trick. Let's just say I didn't need to add any screens to make this work)

 

Move the camera to the front so it is facing forward. The camera view will now match the direction of travel. Problem solved.

Or maybe look at this thread:

https://www.jaguarforums.com/forum/s...estion-268529/