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View Full Version : TR2/3/3A Convert TR3 to negative earth or leave it be?



tdskip
06-16-2009, 02:23 PM
Need to make a decision before I order the Pertonix....

I'm leaning on converting her since it opens up more possibilities of other electric bits...

She's already got a TR4 engine in her so originality isn't going to be her focus...

What do you say guys?

TR3driver
06-16-2009, 02:27 PM
First thing I did! Unless strict originality is a concern, I see no downside at all.

martx-5
06-16-2009, 02:28 PM
Convert it to negative earth.

tdskip
06-16-2009, 02:29 PM
Boy - could you guys be any quick in providing help!?!? I had to wait like a whole four minutes for an answer. LOL.

Thanks!

Mickey Richaud
06-16-2009, 02:31 PM
Boy - could you guys be any quick in providing help!?!? I had to wait like a whole four minutes for an answer. LOL.

Thanks!


I think traffic held Art up a bit... :jester:

rlwhitetr3b
06-16-2009, 02:33 PM
It is as easy to switch back, if you do find a negative to being negative or a positive for being positive.

hermanmaire
06-17-2009, 07:26 PM
Can somebody tell whats involved when changing to neg ground?

Thanks

TR3driver
06-17-2009, 07:45 PM
If the car is otherwise totally stock (no radio), you just switch the connections at the ammeter, coil and battery. Everything else works equally well with either polarity.

You'll also need to re-polarize the generator. There are different ways to do this, the best IMO is to take the yellow/green wire loose from the 'F' terminal on the control box, and momentarily touch it to A or A1 terminal. The easiest is to just jam your pocketknife (or similar instrument) in between the F and A terminals. That causes more sparks, but saves taking the wire loose and putting it back. Either procedure is done with the battery connected and the engine off.

Things get more complicated if you have a radio, electronic ignition or electric fuel pump. Some of them can be switched or rewired for negative ground; many cannot and have to be replaced with the proper version.

Got_All_4
06-17-2009, 11:34 PM
Wow what timing! I was logging on to search this very question. 20 some years ago I installed a voltage inverter to be able to run a modern radio in my TR3. Last summer while driving the car for work something shorted out and burned up the wires to the inverter. Thats a weird sensation going down the road and smoke starts pouring out of the dash and lots of it. Quick thinking I took the 2 water bottles sitting beside me and squeezed them so the water shot under the dash. It put it out. The one time I didn't have my fire extinguisher with me.

Noticed all the talk lately about switching to positive ground in 3s and the many benefits. My new radio and possibly an alternator conversion in the future. Thanks!

TR3driver
06-18-2009, 12:04 AM
20 some years ago I installed a voltage inverter to be able to run a modern radio in my TR3. Last summer while driving the car for work something shorted out and burned up the wires to the inverter. Interesting story, thanks.

I was idly wondering the other day if there would be a market for a modern solid-state "ground converter" with enough oomph to run a fair sized stereo. I didn't go as far as sketching out a design, but it looks like power FETs are cheap enough and there are all sorts of controller ICs available. Only other problem would be a suitable transformer (which would probably have to be custom made).

But I would guess that most of those who are purist enough to care about ground polarity are also not going to want a garish modern stereo in their antique car, so probably not enough market to be worthwhile.

There are some units available, but they use older technology and don't put out much power.

angelfj1
06-18-2009, 04:58 AM
You do understand I trust, that if you proceed your membership will be duly canceled. :devilgrin:

hermanmaire
06-18-2009, 02:20 PM
If the car is otherwise totally stock (no radio), you just switch the connections at the ammeter, coil and battery. Everything else works equally well with either polarity.

You'll also need to re-polarize the generator. There are different ways to do this, the best IMO is to take the yellow/green wire loose from the 'F' terminal on the control box, and momentarily touch it to A or A1 terminal. The easiest is to just jam your pocketknife (or similar instrument) in between the F and A terminals. That causes more sparks, but saves taking the wire loose and putting it back. Either procedure is done with the battery connected and the engine off.

Things get more complicated if you have a radio, electronic ignition or electric fuel pump. Some of them can be switched or rewired for negative ground; many cannot and have to be replaced with the proper version.

Thanks Randall,

That sounds easy enough but I will probably still end up having a problem so I might be back with other questions.

TR3driver
06-18-2009, 04:06 PM
so I might be back with other questions. Nay problemo! Lots of good folk on here, so someone will help out even if I'm away.

Probably best to start a new topic with your particular question in the subject, tho.

Got_All_4
06-18-2009, 08:02 PM
I didn't need much power. Only running a AM FM cassette player and no other accessories. Just used the stock generator too. It was mounted to the underside of the glove box not only for convenience but I was trying to isolate it from a ground. This was before i purchased the converter. Also had to cut the ground wire from the antenna so it would not short out. The few car shows I've been in some participants questioned why I mounted it there. For one I never liked the dealer installed radio boxes in front of the shifter.

My antenna broke off recently so my hope is to now replace everything. Update the radio, better antenna and this should now be possible with the negative ground conversion. As for a market , can't be sure. Don't see many radios installed in TR3s.

TR3driver
06-18-2009, 11:49 PM
I didn't need much power. Only running a AM FM cassette player and no other accessories. Right. But for example my CD-MP3 player is rated 20wRMS into 4 channels, so it can draw upwards of 10 amps.

And you'll never see it unless I happen to leave the glove compartment door open <<GRAEMLIN_URL>>/grin.gif