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Allison XR700 and Lucas Coil - Black is positive?

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DinoBambino Dean Sabetta
Columbus, Ohio, USA   USA
Hi! First-time post here!

Love the 1978 B in my garage, but in poking around, found that the Allison XR700 (1985 manufacture) is wired exactly opposite of its tag - purple to ground, black to positive and red to negative. The car is negative earth - and switching the wires leads to car not starting.

This seems counter-intuitive. Help!

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pleblanc1206 Avatar
pleblanc1206 Gold Member Pierre Leblanc
Saline, MI, USA   USA
1974 MG MGB GT "The MG"
2013 Scion FR-S
I had one in my 74 BGT and can only confirm that purple was connected to a grounding screw on the side panel. The black and red went to the coil but I can't remember the specific connections. Sorry.



1974 MGB-GT: black-label overdrive, essentially stock detoxed engine, Schlemmerized distributor.

MadMax133 Avatar
MadMax133 Max Fulton
Durham, North Carolina, USA   USA
Dean,

Now check your coil WIRES. (The coil will actually work, though less effectively, if wired BACKWARDS).

The Allison wants Red to be to your WHITE (12v) wire and Black to go to your White/Black wire (tach). (Which should be + and - on your coil, respectively).

HTH,

M

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DinoBambino Dean Sabetta
Columbus, Ohio, USA   USA
See, that's the weird part - black/white is on negative, but red is as well. I don't have a white wire on the coil. Obvious question: should I?

I really do appreciate your thoughts and your time!

MadMax133 Avatar
MadMax133 Max Fulton
Durham, North Carolina, USA   USA
Dean,

Okay, as it's a '78, you probably have a white/GREEN wire on the coil? This is the 6v wire from the previous ignition system. (The result of the white/pink resistance wire). The 2nd of the white/Greens is the 12V jumper wire from the starter (so, it'll show 12V when cranking-- but less when running.)

You need to check TWO things @ this point:

1) What is the COIL? There are markings on the bottom OR it's a specific colour (Like "Lucas Gold" or "Bosch blue" or "Heavy Duty Black Coil from AutoZone.." :-p ). If it says "15P6" this is also the 6v coil and you need to get a 12v coil. It needs to say "12" in there somewhere (HA12, for instance.) This is long term reliability stuff......

2) There IS a white wire in that ignition system. You just have to find it. :-) a) there might be a ballast resistor where white wire goes to white/blue. The white is your 12V.... (check it to be sure, natch.) OR .... b) you can also do a simple tap from the white side of your fuse box and run your own 12V wire to the + side of your (now) 12V coil!

As for the Allison only working when wired wrong-- beats me! :-) Perhaps you've trained it to be positive ground? If it works as it was, leave it. At this point, it will work for LONGER if it's connected to a 12V coil getting 12V... (I suggest the Gold Coil, if you need to get another, because this is internally ballasted and thus works for all available ignition systems.)

Lastly, IF you haven't found a good parts source, might I suggest Brit-Tek? He's an MGB specialist.

HTHM,

M

DinoBambino Dean Sabetta
Columbus, Ohio, USA   USA
Played with the wires to the best of my ability - I'm stumped! It's been "trained" since 1985!

The white/green wire is there, indeed - but when attached, the car will not start. I am taking your very sage advice and leaving it be - but I would really like a tach that works - and this setup ain't making it (I've tried two other Smiths and an aftermarket - nothing. And no signal from the coil.)

As many have said on the board, the tach is just "swag"

BumbleB74 Avatar
BumbleB74 William Milholen
Tidewater, Tidewater VA, USA   USA
I think the installation directions are in the Tech Library, or can easily be found using Google!



1974-1/2 Roadster, "Bumble Bee", Corvette Yellow - in shambles, wire wheels
1976 Roadster, "Virus", Sandglow - "driver" condition (stock + 32/36 Weber DGEV, cast iron header, 25D distributor), bolt on wheels, ON the road!

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