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MG MGB Technical - Crane XR700, PN 700-0231 Ignition System

pertronix XR700 ignition system, and am totally stumped to try and get the tachometer to work properly. It does work intermittently, but I believe inaccurate. System is an original USA negative ground, 1972 MGB.

1. Wire when working:

Ignition switch to tachometer to + side of coil. Yellow wire to
James Huggins

James I don't understand your hook up in item 3, but I believe you said you are not using a ballast resistor. I assume you have a RV1 1433 tachometer. If that is what you have it should be wired to the positive + terminal on the coil just as in the set up with points. That said I had problems with tachometers on one car I converted to a Crane system. Look at figure 27 in the Crane instructions. It's easy to remove a loop if the loop is external but the three tachometers I tried had an internal loop and it's difficult to remove a loop with the internal system. All my tachometers would work but they weren't very accurate. There is an adjustment on the rear but I couldn't trim it enough in any of them for the desired accuracy. You tachometer should not be hooked to the negative coil terminal.

Maybe the mechanic you talked to has no problems when using a Pertronix, I have never tried one but I have seen lots of posts where people installed a Pertronix system and had tachometer problems. So it's not a sure cure for your problem.

I cured the one I had by changing to the tachometer used in 73 and later cars. It's an RVC 1410 tachometer and hooks to the negative coil terminal.

You mentioned your car will not run, I would temporarily direct wire the coil from the white wiring at the fuse box and see if the engine runs without the tachometer in the circuit. You need to get the engine to run first and sort out the tachometer after the engine is running properly.

Happy New Year to you, hope you get it going.

Clifton
Clifton Gordon

Nothing wrong with the Crane XR-700. I have had one on my GT from 1989-1998, replaced with a Pertronix unit from 1998-2000 when the Crane inexplicabily died, and then replaced that with another Crane XR-700 unit from 2000-now. All of these have done fine, but the Pertronix unit went into a fit of intermittent operation during its second year, so I replaced it with the Crane unit I had left over from my MGA.

Clifton is right, you need to isolate the tach by by-passing it to get your engine running. If it doesn't run without it, you have problems elsewhere.

You can take a look at how I wired my unit into a 1968 GT in scan of my wiring diagram I will post to you.
Bob Muenchausen

Also, note that if you are using the Crane Coil with the ballast resistor, the coil resistance may be too low or high for the Smith's tach to work properly.

I use the Lucas Sports Coil for straight 12VDC (with NO ballast resistor) rather than the Crane and feel that this combo should work well for you as it has for myself. However, James, I did use a Jacob's "Energy Coil" with the Crane XR-700 WITH a ballast resistor between the White tach lead and the coil positive (+) lead with no problems for years.

Let us know what you find is the problem.
Bob Muenchausen

Hey Guys,

Thanks for all of your replys. I must say this is the most friendly portal I have ever been in.

I am sure I am wiring everything properly. All is pointing to a bad tachometer.

Yes, mine is a 1433.

Thanks for all the help, will try another tach.
James Huggins

hi i had variuos problems with thje crane system.i had to block the vacume pipe for it to work
daren

This thread was discussed between 28/12/2006 and 31/12/2006

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