This winter I decided to completely rewire the car and remove much of the stock wiring that existed but was non-functional.

To make a long story short I ran a ground wire from battery to the rear chassis (chromoly). I ran a "clean" ground inside the car for my circuit board. MSD was as instructed grounded and powered directly to the battery.

Other non-critical items (dirty buss) were grounded to the chassis just like any K&R diagram would instruct you to. Motor grounded to frame with braided CU - and a heavy dedicated battery cable 4 gauge all with top of the line wire.

Everything worked perfectly except when I would hit the starter it would trigger the timer in the grid to start the timer for the electric shifter.

After many hours of diagnosis I finally figure out that the ground on the back of the car was insufficient. I learned this by running a dedicated #4 ground wire from the battery negative to the starter mounting bolt. Once I did that everything was perfectly fine.

Moral of the story - DO NOT RELY on the frame or chassis to carry your ground circuit. Despite everything else working (fans, pumps, lights etc on the front of the car with the single ground in the back - it was still causing issues.)

The trigger was getting set off by the signal coming back up thru the transbrake solenoid to the blue trigger wire. I figured that out within minutes and confirmed it by unplugging the solenoid and it would stop. The bigger problem that took forever to figure out was the WHY. Thanks markemark for your assistance.

At any rate - make sure you run an extra ground wire to the front of your cars.

https://photos.app.goo.gl/DddkUkFysWpE9kMZ8

This message has been edited. Last edited by: ski_dwn_it,

I have found this also. A good way to check circuit is to do voltage drop testing. Basically attach a voltmeter to each end of the circuit and load the circuit. Ideally you want less than a half volt of drop for the entire circuit. Starting circuits are typically tougher because of the loads involve. It will also show you if your wiring is large enough to support the capacity. You can also use it to check any connection or switch. It will allow you to pinpoint exactly where issues are if you have alot of drop in a circuit.

Good luck

I’ve been saying this for years. It always falls on deaf ears until somebody has an issue like you did. I’m glad you found it.

quote:

Originally posted by Wooley:
I’ve been saying this for years. It always falls on deaf ears until somebody has an issue like you did. I’m glad you found it.

I agree. I've always run a dedicated line and for whatever reason I didn't this time. Literally took 15min including making the end, heat shrink, and running it. Dumb. Could have saved countless hours. Fortunately it happened while in shop.

Tonight running dedicated grounds off both heads to that ground point and to coil negative. Another thing most people don't do.

Still blows my mind it found that trans solenoid an easier and better path thru grid.

I will add this, chromoly steel obviously will conduct electricity but it has a much higher resistance than copper. For low current circuits it will work but it's a bad idea to rely on the chassis for completing the starter circuit!!! Way too much current draw even if all the chassis connections are good!

Glad you found it. Chromoly is a horrible ground and conductor. Mild steel much better. But for years we run dedicated ground wires to junction blocks or studs throughout the chassis. Another reminder, don't use nylocks on these locations. Use nuts with star washers or lock washers.

SL...

What I have done is my chassis has several ground lugs welded on. I use them but also have a ground wire from each one going back to battery.

At one time I ran ground wires from heads and starter to good grounds but have got away from that.

About 6 yrs ago I was spectating at an event helping a friend and was asked to look at a racers car that was unable to correctly time using MSD Grid 7730. They said cranking showed one timing setting and running showed a different.

First, looking at their programming I noticed that they were using a launch retard that did not return the timing to full advance at the end of the run. It remained retarded. Then while cranking the car, I noticed the Time From Launch Timer (TFLT) was starting. Momentarily cycling the starter without starting would start the timer. This explained why they would view a retarded timing setting while running. I had them enter a last setting in Launch Retard returning the timing to initial running advance so they could time the car correctly.

They said the car was just professionally wired. I told them to take it back as they have a wiring problem. They disagreed. I told them OK and walked away.

You can never have too many grounds.

I run one to the frame back at the battery. Then run a dedicated ground from the battery up front. Then ground the block to the frame and the dedicated ground.

Thank you for sharing.

Clark

quote:

Originally posted by Curly1:
What I have done is my chassis has several ground lugs welded on. I use them but also have a ground wire from each one going back to battery.

At one time I ran ground wires from heads and starter to good grounds but have got away from that.

I honsetly think that is the proper use for them. It's just a stud/post to stack on. It still needs a wire from the battery.

I currently have two 7720 that need the plug repinned because the coil and main ground are pinned incorrectly.

https://imgur.com/gallery/pRc7LGj

Great input guys! Thank you!

quote:

I currently have two 7720 that need the plug repinned because the coil and main ground are pinned incorrectly.

Pin location and pins not properly locked into position (mostly female pins in male connectors) is not uncommon. I’ve seen the 7730 32 pin connectors assembled incorrectly as well.

I had just about the same problem effecting the shifter solenoid and the trans shift module. The shifter solenoid was pulsing back and forth while cranking. Weird. Talked to tech @ MSD. Sounds like you have an RF bleed. Put the MSD Capacitor on it.

Sure enough problem was Gone. Every car should run the Capacitor.

quote:

Originally posted by TD3550:
I had just about the same problem effecting the shifter solenoid and the trans shift module. The shifter solenoid was pulsing back and forth while cranking. Weird. Talked to tech @ MSD. Sounds like you have an RF bleed. Put the MSD Capacitor on it.

Sure enough problem was Gone. Every car should run the Capacitor.

I had one on my board. Check picture in first post.

Many chose Not to use the battery as the noise filter. Wiring ignitions and other control devices separately with both positive and negative directly to the battery helps avoid interference problems.

Starter, alternator and relay board belong on the dirty bus side of wiring.