Constant switched 12V C Body

OK Back on the Holley Sniper install on 1974 440 Monaco police car after the WHO DAT collapse. Went full boat with Sniper, Hyperspark box, Hyperspark Dizzy, coil etc to head off any mating problems. Holley wants a clean 12volt "switched" with key source. I have a wiring diagram off the net and tried the fuse panel. Every circuit that shows no voltage with key off, shows 12 with key on. BUT when you go to starter cycle, voltage dives. So on to the engine room, blue wire to ballast block has 12v with key on but dives as well on start cycle. Brown on the other side of ballast shows none with key on and 12 on starter cycle. So do I tie them together? Wont there be a "speed of light" interrupt when I release the key after start? Any Sniper folks here? I don't want to fry anything as it is all new and aint cheap. Instruction say don't use starter circuit?????Phish

C body, made my on in tank mod for pump etc. Thanks

Used a relay, control the relay with the switch 12V signal, Supply the feed to the relay directly from the battery positive.

DUH!!!!! Thanks, why didn't I think of that? My claim to fame, I know what I don't know. Love this board. Happy New Year Phish

Probably because you have so much new stuff to add on you're mind isn't thinking about the small stuff right now.

Do I grab 12v at the starter relay on firewall near brake booster (which has a fusible link) or just come direct from battery with an inline fuse. Or is a fuse required? Now to figure out the diagram of a relay. Thanks

Where the following link shows "switch in dash" substitute switched 12v

https://itstillruns.com/wire-automotive-relay-4912752.html

You can tie in to the starter relay connection that is probably a cleaner setup, always use a fuse, fusible link or circuit breaker.

I have read through a number of posts on a few Mopar Forums and I have never seen a better, clearer method of accomplishing this. I am doing an EFI build as well and was still wondering how I would get past the voltage loss during the start-to-ignition phase. Thanks very much!

Just make sure you don't lose the "switched 12v" when the key is in the start position. Since you're ignition setup isn't going to need the ballast feed you can tie the two wires together to control the relay if you need to.

On a somewhat related note, do not run any of the Sniper harness near any plug wires or the alternator. The system is very susceptible to electrical noise, EMI, RFI etc.

A buddy of mine has been involved in a few installations where the harness was installed show car tight and out of sight on the engine and ran into problems from it barely runs to intermittent runs great to barely runs. Data logging showed some pretty strange A/F and tach signal data that straightened up when the harness was moved away from other electrical stuff.

Kevin

Simple diode is all you need.
Less complicated and works

https://board.moparts.org/ubbthreads/ubbthreads.php/topics/2297261/2.html

Not home free yet. I followed the link you sent and have a new relay out of the box. 87 goes to firewall strap ground and test with meter. 85 straight to battery using a temp jumper and test with meter. For 30 spade I just plugged in electric choke blue circuit connector which is switched and checks with meter. 86 (future sniper) just goes to meter for now. It shows 12 with the key off ???????? Which means sniper would be hot all the time. Start cycle voltage drops to 9v. I will try blue/brown ballast circuits tied together to remedy that. BUT why is 30 spade hot with the key off? I am doing something wrong. Thanks Phish (Stephen 337-499-4435) heading back out to shop.

OK that sketch does not work in South Louisiana. Boyd came by and straighten things up. 85 = ground; 30 battery; 86 switched (will need to tie brown and blue wires) and finally 87 to new sniper. Key off, no power, key on 12volt, starter spun voltage still dives but I haven't spiced those yet. Thanks again.....

Using the electric choke circuit on the relay voltage drops to 0 when cranking engine. I joined the blue wire coming into the ballast with the brown wire going out of the ballast and installed on relay. I get full 12v with key on and voltage drops to 7.5V gradually while cranking. Does not go to 0 at all. Is that as good as it gets? Will the sniper start with that "switched" circuit fluctuating 12 to 7ish? I have not wired anything but a tester so far. Thanks Stephen

With a hot battery (car has been parked) the voltage drop is negligible running the starter. Waiting on aircraft RTV for the tank sealing which gets here Monday. Should see if it runs then. Will get back here for timing settings. Thanks

Why all the headaches, just add a diode, easy.
You’re making this way harder than it needs to be.

And will add the voltage is always going to drop when the starter is engaged due to the draw on the battery

Part number? I hate headaches

Using a diode puts all the EFI and ignition current draw thru to old wiring and switch. Pretty sure that's a lot more than it could handle new.

The starter is a massive current draw and it will drop the battery voltage, no way around that. What is the minimum voltage the instructions say you need?

I read around 10v to start Sniper. You have to spin it about 3 seconds to get to 10 and that is with an old battery. I have an extra mini starter combined with a fresh battery, she should light up. I did the relay on the firewall and used the stock blue electric choke spade on the relay. Spiced the brown coil wire to the blue along the valve cover looms so this car can go back stock with no problem. If I can find fuel resistant RTV locally, try to start and break in new bullet today.

Initial timing at 15 and WOT 38 for a stock 30 over 440. 10.5 to 1 ????? Thanks

10v is actually pretty good. Congrats on getting it to run.

Not running yet. Storm "What'cha'ma'call'it" took out the power. Trying to finish tank and install. Get back to you soon. Thanks Phish

I just hooked one up on my Satellite.8 injector Xflow. I connected the pink wireto the wire feeding the voltage regulator. This point on the 67 feeds directly from the ignition switch. Yes, the voltage will drop when the engine cranks, because that's the battery voltage at that moment. It works fine.

Followed the instructions and she fired right up. SWEET. Unfortunately due to a faulty filler neck grommet at the tank, no test ride. Sounds wicked. Sniper, thanks for the relay setup. Lots of wires to clean up. Here is our tank mod. Thanks again. Stephen

Excellent

Thanks for further clarity.

Totally confusing to me. But I am not an electrical genius.

You have a PM. Thanks

Runs GREAT!!! Monaco next. But we are pulling tank again to construct a baffle for low fuel performance (surges with only 5 gals in it). Also ignore the pic date, need to get my Grand Daughter to show me how to clear that. Phish