Electrical genius needed

hound dog · #1 (**permalink**) 10-20-2002, 05:22 PM

I am expecting to finally get my cobra on the street next week, but only if I can get some help with an electrical bug. I'm using a MSD 6AL ignition with MSD distributor amd MSD coil. When the body was off I fired the engine in the chassis and everything seemed to work fine. Now after wiring the car I have no fire to the engine at all with everything hooked up by the book. If I remove all the harness wiring from the coil and just leave the MSD hooked up the engine will crank but not run. It cuts off as soon as I release the switch. I don't have a ballast resistor in the system anywhere and the wiring harness calls for one between the coil and one of the wires. Didn't need it before, do I need it now? As for harness wires, I've one for the tach on the negative side of the coil, the one for the ballast resistor on the positive side and one for something else on the positive side (one of which throws a serious spark when grounded and not hooked to the coil).
Come on guys, if I can't get this fixed I ain't ridin'.

h dog

DavidWard · #2 (**permalink**) 10-20-2002, 05:43 PM

Did you wire it up per MDS's instructions? I'm using the same set-up, except I'm using an Accel coil. I'm not using a ballast resistor. I wired per their instructions and it works perfect.

BTW, my tach is not hooked to the coil. It's wired directly to the MSD module.

David

hound dog · #3 (**permalink**) 10-20-2002, 05:57 PM

Yep, per MSD's book and Unique's. I've also got an e-mail into Unique.
h dog

Slow Dawg · #4 (**permalink**) 10-20-2002, 06:34 PM

A couple years ago I installed a used Ford module on a friends 302. Thought I'd be a smart a$$ and not use a ballast resistor. Run great for a few minutes and wouldn't start later. Found out we fried the coil. Put on a ballast resistor and a new cheap coil from the local auto parts store and haven't had any trouble since. So, check your coil.

Ron

mr0077 · #5 (**permalink**) 10-20-2002, 06:42 PM

h dog, sounds like you have the coil wired up using the wire intended for the ballast resistor. When you use a ballast resistor, turning the key to the start position (during cranking) sends full battery voltage to the coil (appr. 9-10 volts). Once the car starts and you let the key go to the run position power isswitched through the ballast resistor, which drops about 3 volts and sends 9-10 volts to the coil. You could check to see if you have battery voltage to the coil in the run position, I bet you don't, but you will have it in the start position. If this is it, try hooking both the ballast and the normal coil wire to the coil and see if that solves the problem. Another place to look is the ignition switch, make sure you have the coil and ballast resistor wires on the right terminals.
Good luck.

Jack21 · #6 (**permalink**) 10-20-2002, 07:10 PM

Have same setup only using an Accel coil.

Stock ignition is wired differently than MSD, and you must follow the MSD wiring directions or it won't work. A ballast resistor is NOT used on an MSD ignition.

A stock ignition runs 12 volts to the coil while starting, then drops the coil voltage to 7 - 9 volts when running through the ballast resistor. The MSD, or for that matter a Crane, or Accel, runs about 460 volts to the primary side of the coil to CD ignition only type coils. That's why no ballast resistor.

The heavy red wire goes to a battery+ lead, and the heavy black wire to a chassis ground. The thin red wire goes to ignition hot in run. The tach lead goes to the tach terminal on the MSD box. One pair of leads goes from the MSD box to the coil, and another pair of leads goes to the distributor, assuming you're using a magnetic pickup. Polarity to the coil and distributor is critical.

From the ignition switch, start energizes the starter solenoid. The run position is hot in start, and hot in run. The second wire that went from the starter solenoid to the ballast resistor is no longer needed, nor is the ballast resistor. Any wiring that went from the ballast resistor to the coil is also not needed. Only the wire pair from the MSD box should be connected to the coil.

Spend $20 or $30 at Radio Shack and get yourself a volt-ohm meter (VOM). A handy aid for checking wiring continuity.

Also check fuses for some you may have blown while experimenting.

jeff harvey · #7 (**permalink**) 10-21-2002, 04:28 PM

Sounds like what I did. Ran fine without a body didn't with one. Was on my way into town for new parts (more) then it dawned on me, can't ground to fiberglass. Don't know if this is your problem but I tried to make it harder than it really was, just needed a little piece of wire.

decooney · #8 (**permalink**) 10-21-2002, 05:07 PM

Hey,
not to simplify things, but in addition to following the MSD instructions, exact, and the previous advice here, be sure to "check all wires and terminals for loose connections". Do you have a ground strap to the solenoid from the chassis? My friends Unique was running intermittent ingition for several months, and he could never figure out why. He would let the car sit in the garage out of fear of getting stuck on the road. After a long search by several friends of his, I found out that the wire into the MSD distributor had no resistance... upon close inspection, the wire on the pickup coil had barely separated itself. (get an ohm meter! We replaced the coil pickup/wire, and it's worked great ever since. He also added a solid ground strap, and spark went from dim to zap!

Possible Cause in his case (simple stuff):
after mounting the body, he had wire-tired everything tight, and some wires had been stretched and yanked around a bit. The wire into the distributor just got pulled a bit too much one day. The ground strap was a must too. Good luck.

The simple stuff will get ya every time...

Duane

hound dog · #9 (**permalink**) 10-21-2002, 07:13 PM

OK maybe I'm a little thick, but here it is. By having the orange and black wires from the MSD hooked to the coil along with a yellow and white from the harness I was trying to run a mix of two ignition systems. Now follow me closely...the small red wire from the MSD (ignition hot wire) was connected to the "I" side of the relay along with a yellow wire (maybe the same yellow as went to the coil). This appeared to be hot all the time the switch was on. However it was the white wire that went from the ignition switch to (I suppose) the coil that the red MSD ignition hot wire should have replaced. Removed the ignition switch, removed the white wire and replaced it with the red MSD wire, taped the ends of the wires at the coil, and the engine fired the first time! Apparently as wired before the engine would fire off the yellow wire from the relay but as soon as I released the switch the engine would cut off because it was the ignition hot terminal that needed to be connected and not just a hot wire. Jack21, pretty good ole buddy,spot on, but a special thank you to Alan Weaver for helping me get my colors straight

h dog

Jack21 · #10 (**permalink**) 10-21-2002, 08:42 PM

Couple of other tips that may help out.

Oops. Forgot the ground strap. The engine must be grounded to the frame, and the engine, and frame must be grounded to the battery ground.

And particularly on a Cobra, because it vibrates more than most cars do (and if something can jiggle loose, it will) run redundant ground wires back to a common point, and ground the common point to the battery.

Murphys law on Cobra electrical systems (given the above vibration characteristics) is; all crimped connections will eventually fail due to vibration, strain, or corrosion. Meaning what worked fine for years on your LTD, won't work on your Cobra.

Remove all factory crimped connectors, then cut the wire to the correct length to loosley fit the application. (You can remove a lot of excess wire from pre-fab wiring harnesses this way) Slide a piece of shrink wrap tubing over the wire to be connected (Radio Shack, or hardware store electrical dept has shrink wrap tubing). For a splice, use a butt splice connector. A termination a spade lug, or ring lug. Use non-covered terminals, or remove the vinyl insulation (that's what we're using the shrink wrap for) Crimp the wire with hand crimpers to the connector to make a good physical connection. Then solder the connection. Take a little non-moly wheel bearing grease (with a Q-tip) and coat the connection. Put the shrink wrap over the connection, and heat it with a hair drier until it's tight. (I use a $20 hobby shop Mono-Coat gun/blower)It's time consuming and tedious, but you have a connection that will never vibrate loose, or pull loose, or corrode.

MSD system caution. If you use the MSD accessory parallel wired capacitor on the power side of the box because of radio noise, or whatever, the capictor terminals must be protected (insulated) at all times from metal contact AND SKIN CONTACT. Even with the power off, and the battery disconnected! Laying a wrench, or your forearm across those terminals, once the capacitor has been charged by powering the ignition on, will do some serious damage.