Hey guys, a few weeks ago my mate came to me with an old Jaguar, cant remember year or model, but it had a 12v positive ground system (meaning chassis is at + potential)
This also meant I couldnt just wire in a standard negative ground head unit for him the normal way, and I also nearly told him I couldn't do it, but a bit of quick thinking and I changed my mind and said no worries.

Here's how to do it

You will need:

-standard 30A horn relay

-relay base

-the stereo

-required connectors or solder and heatshrink or whatever


Here goes:

Connect Yellow wire of stereo (Battery +) to the chassis with a ring terminal to a clean point as you would a ground wire.
Connect Black wire of stereo (Ground -) to the battery - feed to the ignition switch using a 10A fuse at the splice.
Connect Red wire of stereo (Acc +) to terminal 87 of the relay
Connect Terminal 30 AND 86 of relay to the chassis with a ring terminal and 1A fuse at the chassis
Connect Terminal 85 of relay to car harness negative acc power wire.

The stereo should now work as it would in a negative ground car.

Attached is a diagram

Hope this is of help to anyone

-Ben

This is ok as long as the case of the stereo never touches the metal of the car - blown fuse instantly.

If you mount the stereo into a marine-type plastic box, and use isolators (such as stinger SGLI) on the RCA outputs, then you'll be right. Also, you would need another relay if you want to run the remote out for amp power too.

good point Pulse-R, never thought about that when I put the stereo in, must have been lucky i guess.

yeah im not going to even go into installing an amplifier in these cars. Besides, if you are doing all that to a car that old with a positive ground system it might as well be rewired.

Nah, just swap the terminals on the battery around.

.......and reverse the direction of the starter, the wipers, lose half of ur ignition power...........kill everything basically................i like it

nah seriously like i just said u cant just swap the battery terminals around............otherwise I wouldnt have written this tech article.

And about the case of the stereo touching the body, obviously precautions must be taken. And about the RCA's, if you are going to all that trouble to put a stereo in, might as well rewire the car.

we have a car like this at work atm. an old astin martin with positive ground. some idiot decided to install a radio & therfore switch the terminals. because of that, all of the fans were sucking air instead of blowing, wipers stuffed etc etc. we have used a relay to fix the radio installation, & we have nearly fixed all of the problems with it.

tell me, when putting a head unit into a positive ground car, should I fuse at the constant negative splice to the ground wire of the stereo or at the constant 12v+ wire going to the positive chassis. Likewise for the feed to the relay for accessories.

The link to the digram in the first post doesn't work anymore.....Could someone send it to me boost_me@aapt.net.au....Thanks

Matt.