MSD ignition

Engine's been running fine for a while now until yesterday. Fired her up, ran smoothly until I switched off the ignition via the ignition switch but the engine continued to run so I turned off the battery cut out switch, the engine continued to run until it the fuel bowls emptied.
I've tried to start her up today but no joy, I have no spark at the plugs but I do have 12 volts in-coming to the MSD ignition.
Any ideas?
Also, I'm sure the wiring is correct but can anyone cofirm the wiring for standard GTD wiring to an MSD 6AL ignition?
 
Paul, there are two 12V connections to the MSD.
The main heavy red wire must be connected directly to the battery or a convenient place such as at the starter motor main feed. You say you disconnected the main battery switch and it still ran on but are you sure this cuts the feed to the MSD? Check it with a meter.

The lighter red wire should go to a switched ignition feed. Run on is a common problem as the MSD only needs a small current to continue working and this may come from other wiring also being connected to the ignition feed going to the lighter red wire.

I think Paul Thonmpson is an expert in this area perhaps he can comment - also try a search, I am sure this topic has been raised before.

CU at Goodwood this year??

David
 
Hi Paul

As Dave says - the MSD requires a direct connection to battery positive (not via a fuse) to its thick RED wire and a good ground. After this, the thin RED wire is used to turn the MSD on and OFF.

If the this red is taken to +ve, MSD SWITCHES ON and if it is taken to gnd - or open circuit, MSD SWITCHES OFF. As Dave states, it takes very very little current to switch the MSD on, so ensure that your thin RED is correctly wired. A reverse feed, from FANS for example, will carry enough current to turn the MSD ON.

Were the fans running when you tried to switch off? if so you may require a diode fitting to prevent run-on.

The kill switch tecnically should kill all electrical circuits. Often it is not wired correctly and the engine will run on from the output of the alternator - a bit like a latching relay.

Hope this helps - if not, call me and I'll see if I can help further. /ubbthreads/images/graemlins/grin.gif
 
Thanks for the reply guys.
The thick red wire is connected directly to the battery & the thin red wire is connected to the +ve wire.
The only other thing I can think of is that I am using an Elliot tacho so I have had to join the white/black cable to the green, these are normally connected seperately to the Smiths or Stuart Warner tachos but not req'd for the Elliot gauge. Should the white/black be connected to the live side of the Elliot tacho?
Paul, yes the fans were running when I switched off the ignition. The worrying thing is that the engine will not start now.
 
Hi again

When you say the Thick RED is to battery - where is it actually connected? starter? Alternator? directly to battery?

The thin red is currently connected where? to what +ve point?

Also - I presume the ONLY wires to the coil are the orange and black pair from the MSD? - no other connections i.e. tacho or shift light?

Plus - you are using the MSD Tach output? the female spade on the end of the unit?

To check your MSD for spark - turn on the ignition and momentarily ground the white wire to the MSD with the king lead from coil near an earth. Each time white wire is grounded you should see a FAT BLUE SPARK jump to earth and tacho should jump if connected to MSD tach output.

Be careful testing output of MSD as the coil can have several hundred volts across it's primary (+/-) and the HT output can cause you SERIOUS HARM if you touch it!

Ignition light permanently on? even with ignition off? - could be a reverse feed to +ve ignition circuit.

Finally try pulling the Fans relay located in the nose area as this will isolate a common reverse-feed cause. Suitably located diodes can cure most reverse feed problems.
/ubbthreads/images/graemlins/frown.gif
 
Two somewhat related comments:

My engine continues to run for about 1/2 second after the key switch is turned off with a MSD 6AL. Ideas? Still getting small current?

The MSD creates an unbelievable spark!! I was doing a compression test and pulled the plug wires from the plugs and coil wire out of the coil cranked the engine over (should have disconnected the distributor wire from the MSD Box). The coil was arcing out of the coil and over to the negative small coil wire with a fat blue arc. Must be 2.5 inches!
 
When I tried to discover the correct plug gap for the 6AL a very helpful guy at MSD said 'for compression ratios below 10.5:1, start at .050 - .060" and increase by .005" until you can't feel any improvement. For a CR of 10.5-13:1 start at .040-.050", above 13:1 start at .035-.045"'.
I set the gap at .050" and chickened out!
It takes some mother to produce sparks that powerful!
 
The fault seems to have originated indirectly from the cooling fans. It is possible the radiator thermostat can provide residual current even after the ignition switch has been turned off.
Word to the wise, DO NOT use the battery master switch to isolate the engine should it run on. The alternator could use it's 'brain' to up the ampage to compensate for lack of battery power resulting in a fried MSD unit such as mine.
This is a bit like bolting the stable door after the horse has bolted, but it seems a common fault on the GTD is residual current from the rad thermostat. A fix is to install a diode in the supply to the thermostat or a switch to isolate the current should run on occur.
Also, another common fault is residual current from the ignition light on the dash. Again a diode installed in the line should fix the problem.
Unfortunately my MSD unit is fried, so a new unit wil probably be the best option as opposed to returning it to MSD in the US for diagnosis & repair. One step forward 6 back!!
Any companies in the Uk who can repair MSD ignition units? Or does anyone have a spare, good 6AL unit they wish to sell?
 
Hi Paul -

Having been 'inside' a few 6AL's in the past, I may well be able to repair your faulty unit. I also have a spare unit available that you could use whilst yours is sorted.

Call me tomorrow (I've mailed you my mobile number) and we'll see if we can sort your existing unit... /ubbthreads/images/graemlins/smile.gif
 
Paul,

It's not spare, and I don't want to sell it, but you are more than welcome to borrow my 6AL unit while my car's off the road if it's any use?

Simon
 
HI paul
i had similar problems installing MSD equipment;suggest you do not connect tacho whilst installing;when everything works witouth tacho you will most likely have to adapt your tacho;if it is the case,let me know,i have an adress in the uk
rgds
fred
 
Thanks Paul, I'll contact you tomorrow (thursday).
Cheers Simon, that's a very kind offer I'll let you know how I get on.
Fred. The tacho idea is quite interesting as I have only recently connected the tacho & the engine was running fine prior to this. That said the tacho was working fine up to the engine run on problem. The tacho I'm using is an Elliot, if that makes any difference?
Many thanks to all for your input.
 
Paul,

I have an MSD Tach adaptor if it turns out you need it. My tach wouldn't work with the MSD with or without the tach adaptor, so it's with speedy cables being looked at.
It's no use to me so you are welcome to it.

Simon
 
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