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MG Midget and Sprite Technical - Bu**er, bu**er, Bu**er Pertronix!

Just spent the evening fitting my new pertronix, turned on the ignition having triple checked the connections to be greeted by clouds of smoke from the Pertronix wires. I'm assuming I've now fried the unit but what did I do wrong? Engine won't start anyway but turns over.
With points I had one white wire coming from the positive coil and two white and black from the negative. In a previous thread Dave O'Neil suggested I had an RCV tacho and one of the black and white wires ran to it, the other going to the points.
I simply piggy backed the pertonix to the coil, red to positive and black to negative per the instructions. It ran fine with points previously.

I'm not sure where to start looking but clearly don't want this to happen again. I've read in the archives that the chip will fry if the Pertronix wires are reversed but I definitely has them the right way round. Could my coil have the terminals mixed or is it as "simple" as my having a short somewhere? I'm seeing circa 3.5 ohms across the coil termonals so assume its unballasted. I've got continuity between the dizzy backplate and the body. Where else do I look?
Its half past midnight and I'm really p*ssed off!
Oh and do you think I can swop the fried unit for a new one?
Last sudden thought. I did leave the Pertronix wires loose for the first switch on and they were both lying on the steering column. Could the current be strong enough to short via the steering column despite the insulation on the wires (no bare wires!)
Any help greatly appreciated as always and just glad I didn't try fitting the thing the night before Spridge 50!
Matt 1275 Bucks

Pertronix was really good to work with when I had a failure in the wiring at the chip....So call and be nice 1st...then rip there heads off and spit down there throats...lol. when you get a new one make sure you put an in-line fuse in the system on the next one....

Positive connections
the red pretonix chip wire goes to positive side of the coil, the white MG ignition wire also goes to the positive side og the coil

the negitive connection
....the black pretronix wire goes to the negitive side of coil

IIRC

prop
Prop

Did the wires get pinched inside the cap

.....curious as to why the wires are loose at the steering colomn that they are lying across the column....is it possiable with the movement and rustling of the wires it could have cracked the old brittle insulation. or got schaffed in a pass thur hole in the sheet metal somewhere.

I commend you for being wise to abaondon ship for the evening...took me many years and lots of screw ups to learn how to stop digging, when your in a deep hole, late at night.


prop
Prop

Is you car + or -ve earth?

There's no way the column could wear through the wires in such a short time with no tension on them.

A
Anthony Cutler

Negative earth, 1973 with alternator.
The steering column thing is probably just a red herring. All I meant was that I had not bothered to tidy the wires up for the first switch on and they were lying on the sterring column but fully insulated. It was this area that the smoke was coming from and in my stupidity I wondered whether the current was strong enough to create a short despite the Pertronix wires insulation. It's got to be something else though!
Matt 1275 Bucks

My car is - earth and as I recall the Ignitor red wire is fed directly from the ignition circuit and the black wire goes to the neagtive coil terminal.
Jeremy Cogman

I fried mine too as mine (frogeye) had been coverted to neg earth but the coil was still wired up pos earth.
Is your coil wired up the correct way?
G Lazarus

I've thought about this one Gary but I'm struggling to see how it can be. The car has always been negative earth and the coil terminals are clearly marked +ve and -ve unless a previous owner has done something devious. As I said worked fine with points and maybe I should have left well alone! Is there any way of checking if the polarity of the coil is right before I fry another?
Matt 1275 Bucks

Not sure about how to test but the car will work fine on points with the coil wired up back to front.
Yours though sounds more mysterious.
Perhaps a call to petronix might help.
G Lazarus

As long as you connected the red wire to the coil terminal which had the +ve from the ignition (white) connected to it, you shouldn't have had a problem.
Dave O'Neill 2

Matt, as Gary says, ignore the coil markings as it may have been installed thw wrong way.

Jeremy Cogman

Curiouser and curiouser. I did have the red connceted at the +ve terminal to the white ignition feed. Unless of course I'm going mad.....I am starting to doubt my own sanity. I rang a fairly helpful chap at Pertronix who gave me a few pointers as to testing the LT circuit, most of which I had already gleaned from the archive, so I'll try that tonight. Moss who I bought the gubbins from were completely unhelpful and will insist on sending the unit for testing before giving me a refund. In the circumstances I am very reluctant to pay for another one to have the same thing happen. Is it worth buying a new coil at the same time just to be on the safe side?
Matt 1275 Bucks

All you need to do to check your polarity is put a meter from the positive of the coil and to earth. If that reads a positive voltage then you have it correct. You could then reverse your meter to see if that shows a negative voltage to check the meter.
Bob (robert) Midget Turbo

If you put an in-line fuse between the pos. chip and the pos. coil....you wont have a problem hurting the chip...just buy a handful of fuses....there between 10 cents to 50 cents a piece...

Im curios as to maybe they reversed the wiring on the chip. let me take a look at mine and Ill get back to you in a bit....I really have feeling its in the chip.....after all when they test the chip, they will just say its "been burnt" without any further explantion Is what I fear. at least thats how these situations always work out for me

But unless you got some kind of grounding taking place in the ignition system....(aka) a sheet metal screw going thur the wiring and secured to the body of the car as an example, I just cant see it....


prop

Prop

Prop,

Not sure you want just any fuse, when I have looked into fusing power semiconducters I have been pointed at specific fuses such as "high speed semiconducter fuses", any old fuse may not do the trick as they may not blow quickly enough to protect delicate power circuitry. Any electronic boffins got more info as it's not my field of expertise.
David Billington

Well don't I feel stupid!
I pulled the dizzy again tonight to reinstall the points and noticed that I had nicked the red Pertronix wire presumably when I put the distributor cap back on and it must have been shorting against one of the retaining nuts. Put it all back in again thinking that I must have fried the chip judging from the smoke previously coming from the wires, turned on the ignition - no smoke-turned the key and damn me if it didn't fire first time without even needing any choke. Just goes to show you shouldn't rush these jobs particularly late at night. Just need to check the timing, tidy up the wires and give the carbs a much needed tune and all will be well with the world again!
Thanks once again for all the valuable advice and sorry to have used all the collective grey matter on the BBS on something which was my own carelessness.
Even without adjusting the timing it seems my idle is now a lot smoother so hopefully all the hassle will have been worth it. Got lots of practice and cramped fingers in pulling the dizzy too!
Matt 1275 Bucks

Just read back through the thread and what do you know? Prop had it first time! Still can't quite believe I didn't destroy the chip though!
Matt 1275 Bucks

Shorting the red wire wouldn't destroy the chip. Might burn your loom out, though...and take the rest of the car with it!

:o(
Dave O'Neill 2

Great news Matt,

Im glad to hear that, I just got back from the shop from looking at mine to check the wiring....so glad you dont need the info.


Hey david,

thats a good point, I have a 15 amp in-line fuse between the pos. coil and the chip maybe I should install a 10 amp instead...Ill have to play with that...

frankly scence my mess from 18 months ago, its ran great....so the fuse is more of a safty blanket for piece of mind...really dont want to blow another chip as priccy as they are.


prop


Prop

Matt (and anyone else who may be interested)......I am thinking of installing Pertronix in my B GT after points problems.

Have found that you can order Pertronix from an outlet in the USA for under $80 (yes, dollars, not pounds). It is then delivered from their depot in the UK.

Seems a good way to avoid the inflated prices we pay for everything over here.

Clark.
Clark

Clark, that's very interesting - care to share details? please email me if you don't feel you can make it public...
TIA
David Smith

David,

Ive only just come across this today....some internet browsing at lunch time. Have also checked up on a few forums, and from what I read everything seems genuine.

Have a look at *Retro Rockets* website.......they explain how to order and have a very comprehensive stock of ignition systems, coils, etc. They do have a warehouse in England.

Its about $78 for the ignition system and $35 if you want to use their coil, for my GT.

Tempted to give them a try, once I check out my distributor for compatibility with Pertronic.

Clark.
Clark

I found them yesterday when I was trawling the web for Pertronix tips! If only I'd done this before placing an order with Moss I could have saved about 30%!
www.vintageperformance.com/retrorockets/mg.htm
(Can't work out to make it turn into a hyperlink)

Matt 1275 Bucks

Mine came from petronix USA ordered and paid in Dollars but it was posted from an address in the UK.
No problems whatsoever (apart from the afore mentioned frying).
G Lazarus

This (for the 4 cylinder cars obviously) is now looking quite cheap with the dollar exchange rate.
do you think it's worth getting?
http://www.lbcarco.com/cgi-bin/gen5?runprog=lbcnews&page=/newsletter/news060108.html&o=
G Lazarus

No idea but will it take a 25D4 side entry cap?
Matt 1275 Bucks

I think like the Aldons these are based on 45D4s

from the retro rockets site

"Cap & Rotor (also fits Lucas 45D distributor)"
http://www.vintageperformance.com/retrorockets/british_a_&_b_series1.htm

I forget the part number now but 45D right angle caps were available in my local halfords last time I looked.
Dean Smith ('73 RWA)

45D4 side entry caps are available on ebay v cheaply - look for MG Maestro 1600, they just need a minor mod to work with spring clips rather than screw fittings.
David Smith

David....thats your Rover wings and 2nd hand bonnet in my avatar pic.

The modification mentioned can be seen here (albeit for an Aldon dizzy)

http://www.eatworms.org.uk/album/album2.php?album=midget-Ignition&mode=page&index=2
Dean Smith ('73 RWA)

Dean, glad they're OK.
that dizzy cap is the expensive one, often around £15. My one is different again, and is usually a couple of quid or so !


David Smith

This thread was discussed between 02/06/2008 and 05/06/2008

MG Midget and Sprite Technical index

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