1971 FJ40 Positive Ground System? (1 Viewer)

[MrBG]

Hello All,
I've been a long time fan of this forum, and have been slowly restoring a 1971 40 I purchased last year with the help of all the knowledgable folks on Mud! I've run into a dilemma this past weekend and was wondering if anyone out there can help, as I've been unable to find info about this via search:

I recently did a bunch of work on "Chuggy" over the winter, replacing leaky radiator, old fuel pump, etc., to include LED headlights (thanks to City Racer's site). Once I got everything buttoned up and went to start the truck, the battery was dead as a hammer, despite being on a trickle charger over the winter, being less than 6 months old, and testing okay for voltage before installing back in the truck. I exchanged the battery at Wally World, installed the new battery, and it started right up. Problem is, the LED's didn't switch on. That got me thinking-when I purchased this truck, I noticed it was positive ground. I'd never seen this before, but am admittedly a newb to Land Cruiser wiring and electrical systems in general. I've read it was common on older 6 volt systems, but for the life of me cannot find anything in the Land Cruiser FSMs suggesting they were ever positive grounded. Since I believe LEDs are polarity sensitive, I'm wondering if the positive ground setup is causing the headlight issue (and possibly the issue with my truck eating up a new battery shortly after install).

Has anyone out there heard of certain model years being positive ground? If not, is reversing it back to stock as easy as turning the battery around and swapping the battery cables? I don't want to risk frying anything, but am learning on this car so would appreciate any advice.

 

[73FJ40]

No FJ40 at least since 1969 (and likely forever) has been positive ground from the factory.

Since I have no idea how much the PO changed things, your guess is better than mine on swapping back.

A clue for the reason may be like you said, the LED lights. LED's are polarized such that current only flows one way to light the bulb. If they're wired backwards, they won't light.

Did your PO hook up his LEDs and they didn't light, so he (old school pronoum) swapped his battery cables? I can't imagine the alternator could function as designed with reversed polarity. It's possible the alternator is cooked, and DOA. Does the starter work okay?

I suggest you consider wiring a 20 amp fuse in SERIES with (I believe for 1971) your wire coming from the ammeter (possibly a white 10 gauge wire) so that if something wants to short out with the cables switched, the fuse will save your wiring harness from melting.

 

[MrBG]

No FJ40 at least since 1969 (and likely forever) has been positive ground from the factory.

Since I have no idea how much the PO changed things, your guess is better than mine on swapping back.

A clue for the reason may be like you said, the LED lights. LED's are polarized such that current only flows one way to light the bulb. If they're wired backwards, they won't light.

Did your PO hook up his LEDs and they didn't light, so he (old school pronoum) swapped his battery cables? I can't imagine the alternator could function as designed with reversed polarity. It's possible the alternator is cooked, and DOA. Does the starter work okay?

I suggest you consider wiring a 20 amp fuse in SERIES with (I believe for 1971) your wire coming from the ammeter (possibly a white 10 gauge wire) so that if something wants to short out with the cables switched, the fuse will save your wiring harness from melting.

Thanks for the reply, and for the idea on the 20 amp fuse. I put in the led lights; the PO still had the original halogens from what i can tell. In fact, crazily enough, the only parts on the whole truck that don’t appear to be the original parts from when it left the showroom are a recently replaced starter, dizzy cap (both new oem) and the battery. The old, tired terminal cables look to have been swapped for a long time. The PO before me admittedly knew little about cars and sold it to me mostly because he was spending a lot of money paying shops to do all the maintenance, so whoever did the terminal swap must’ve done it way back (i think I’m 4th owner).

You mentioning the alternator makes me wonder if it is toast; would explain the battery drain. All the other electronics seem to work, and ammeter reads dead center in the gauge (tho it moves back and forth to the click of the turn signal). All the wiring looks pretty original (or at least really old) so not sure if it’s been tampered with. Sounds like I’ve got some trouble shooting to do!

 

[73FJ40]

@MrBG

"I suggest you consider wiring a 20 amp fuse in SERIES with (I believe for 1971) your wire coming from the ammeter (possibly a white 10 gauge wire) so that if something wants to short out with the cables switched, the fuse will save your wiring harness from melting."

I think the wire you need to supplement with a fuse is connected to the positive terminal on the starter.

 

[ToyotaMatt]

what the H#LL is a positive ground all about ?

sounds like a PO term

 

[middlecalf]

Just remember if you switch the polarity of the electric system on your rig you’ll have to drive on the other side of the road and in the opposite direction

 

[MrBG]

Just remember if you switch the polarity of the electric system on your rig you’ll have to drive on the other side of the road and in the opposite direction

Oh sh!t, you’re right! That’s a lot of variables to consider

 

[73FJ40]

what the H#LL is a positive ground all about ?

sounds like a PO term

The OP discovered his positve battery cable was connected to the frame, and the negative cable to the starter. Since he was unfamilar with FJ40's (foreign vehicle), his question was to determine the proper convention.

Note that back in early 1950's, Ford had positive grounds and GM had negative grounds. Some British OEMs had positive ground systems into the 1960's.

So, assuming the OP knew about the aforementioned positive ground convention history, and observing his FJ40 had been wired positive ground, it was an appropriate question to ask.

 

[MrBG]

The OP discovered his positve battery cable was connected to the frame, and the negative cable to the starter. Since he was unfamilar with FJ40's (foreign vehicle), his question was to determine the proper convention.

Note that back in early 1950's, Ford had positive grounds and GM had negative grounds. Some British OEMs had positive ground systems into the 1960's.

So, assuming the OP new about the aforementioned positive ground convention history, and observing his FJ40 had been wired positive ground, it was an appropriate question to ask.

Exactly! I knew some vehicles in the 50s had positive grounds, but wasn't sure when that stopped (from what I've read, early 60's?). The only other Land Cruiser I've owned was an '81 BJ40, which was a different beast entirely. I'm not sure why PO would swap the leads; I'd read online that having the positive ground to the frame helped prevent corrosion, but no idea if that is accurate. The original PO put layer upon layer of rubberized liner on the frame (which I'm trying to scrape off to re-coat the frame properly), so if the anti-corrosion sentiment is true, perhaps that's why he switched the terminal cables. Either way, I have a 20 amp fusible link in-hand, and will be installing it per @73FJ40 's suggestion. I'll report back on how things pan out, I'm hopeful that since most of the truck isn't polarity sensitive, I should be able to do the swap with minimal issues with the possible exception of the alternator, which appears to be the original and not sure yet if it works anyway.

 

[73FJ40]

@MrBG

The fusible link is an excellent long term device, but the reason I suggested a regular old 20 amp fuse is that it will 'Pop" instantly on a short, and they're a lot cheaper than a fusible link.

Hopefully, it won't come into play.

Good luck!

 

[1911]

Just remember if you switch the polarity of the electric system on your rig you’ll have to drive on the other side of the road and in the opposite direction

There were British cars back in the day that were positive ground from the factory (and they do drive on the other side of the road!); I wonder if @MrBG 's truck came from a British Commonwealth market or was owned by someone from same.

 

[middlecalf]

A lot (most) pre-50/60 cars were positive ground.

 

[rainingagain]

Positive ground is pretty old tech. It went away when 6-volt was obsoleted and improvments in wiring casings eliminated it's main reason for existing. Think of all the old school wiring with cloth casings getting wet! I think it was supposed to help with corrosion issues also but I haven't read much on the evidence of that claim. Maybe that's why PO did it? Rust prevention?

Was there ever a 6 volt FJ40?

 

[MrBG]

UPDATE: I switched the pos/negative cables back to the way they should be (neg ground). Ammeter and speedometer still work, led headlights are now functional, but oil pressure, fuel gauges and blinkers/brake lights no longer work. I’m debating undoing the PO wiring versus just putting it back to positive ground and reversing the wiring on the led lights

 

[Toyo_Judson]

Undo the wrongdoings... Chase and obliterate the gremlins... This is the Way

 

[MrBG]

Undo the wrongdoings... Chase and obliterate the gremlins... This is the Way

View attachment 3006043

yeah, i think you’re right; not sure when I’ll get to it as I’ve got a baby due in the next two months. Though the decision may have been made for me, as when i reversed it back to positive ground the gauges still don’t work. I’m worried maybe i fried them, i wasn’t aware they were polarity sensitive…only speedo and ammeter work now, regardless of which way i ground it…well shucks.