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Engine Test Stand Wiring Schematic
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71Vette
Novice
Jan 27, 2018, 8:20 PM
Post #1 of 14
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Engine Test Stand Wiring Schematic
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UPDATE: TESTED THE SUGGESTED FIX AND IT WORKS. THE SCHEMATIC SHOWN BELOW WORKS. Thanks to everyone who helped!
Just wired up my new test stand (no schematics) and it works (!!!) but the engine continues to run when I turn the IGN switch to the OFF position. I think its because I'm running my alternator field wire through the IGN switch (found some instructions online). Its a 10SI with two posts. Aftermarket HEI distributor. Here is my diagram and a pic of the motor/stand. Can anyone advise where I went wrong? Also, havent figured out a good place to plug the + lead from the ammeter into yet. Very basic wiring knowledge... surprised I haven't burned it to the ground yet :-} Thanks for the help.
(This post was edited by 71Vette on Feb 19, 2018, 12:40 PM)
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Tom Greenleaf
Ultimate Carjunky
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Jan 27, 2018, 8:56 PM
Post #2 of 14
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Re: Engine Test Stand Wiring Problem (Ign Switch)
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? Looks like it might be the engine in your user name. If still running for testing it has to be empowering the hot wire to distributor thru IGN switch probably not letting go or not for this set up even for a test run for the engine. Hard to know not so sure just any generic ignition switch will work OK or if an old one for something else isn't working or stuck?
Nice try at the drawing! Tom
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71Vette
Novice
Jan 28, 2018, 7:30 AM
Post #3 of 14
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Re: Engine Test Stand Wiring Problem (Ign Switch)
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Thanks Tom! Ya, that alternator wire running through the IGN switch is the only place I can see that might be keeping the harness energized without the key. Its a new 4 post generic ignition switch sourced from an automotive parts store. I'm thinking about rerouting the #1 Alternator wire to the positive 3 post busbar that I'm using to distribute power to my gauges. The busbar is powered through the relay so it becomes energized when the key is in the IGN position. I just don't know enough about alternators to know if that's a safe move or not.
ps. Thats just a run of the mill 327 with vortec heads that I had in the shop. Working on a sbc 434 for the Vette
(This post was edited by 71Vette on Jan 28, 2018, 7:36 AM)
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Discretesignals
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Jan 28, 2018, 7:37 AM
Post #4 of 14
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Re: Engine Test Stand Wiring Problem (Ign Switch)
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The relay circuit you are thinking about using would solve your problem. Anything to keep enough voltage from back feeding into your ignition coil when you turn the ignition off. A diode or high enough resistance lamp wired in series works too.
You can also put the ignition system on it's own toggle switch. If you put the ignition on it's own toggle switch, you can do tests on an engine that are done while cranking the engine with no ignition, such as compression testing.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Jan 28, 2018, 7:47 AM)
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Tom Greenleaf
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Jan 28, 2018, 8:06 AM
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Re: Engine Test Stand Wiring Problem (Ign Switch)
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The "key" (not the key to switch) is it must have power to HEI either from alternator or elsewhere. You could just test that when off the switch (generic*) is still showing 12v+ and find where it's getting it from possibly unplug alternator first? If it shut off when key is pointed to off there's the trouble. Where's the voltage regulator? Is that old style 4 wire "F" is field when grounded put out max voltage don't do that except thru an incandescent test light limits it from burning up still just for a test quickly.
Yes - I think voltmeter may pick up current from alternator* when off at keyed switch and shouldn't. Lost - there were a lot of alternators that would light a "GEN" light with an alternator failure with keys out all OE all were Oldsmobile by chance left the word "GEN" idiot light despite it's an alternator?
Back: What is this generic switch. Should be temporary "start" if you let go to "run" and off always off might also turn one backwards for "ACC" accessory or not doesn't send power to "RUN" position. If it did just testing it without all the wires that's it.
Test away it's getting power to distributor from somewhere, Tom
PS: * means to me alternator is capable of a failed diode trio inside sending just slight power backwards would be to that "GEN" switch. Those kept working it was just a dim light on dash fixed by redone alternator. IDK why this only did this trick to Oldsmobiles others used idiot lights frequently in 1971 era and same alternators you just "clocked" those so wires hooked up to harness properly not like on the bottom or something---------
(This post was edited by Tom Greenleaf on Jan 28, 2018, 8:17 AM)
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71Vette
Novice
Jan 28, 2018, 8:26 AM
Post #6 of 14
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Re: Engine Test Stand Wiring Problem (Ign Switch)
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Thanks for the help! I'll try rerouting to the relay circuit to see if that solves the problem. I understand the basic principle behind a diode but not the practical application so going to try and keep the wiring as simple as possible. I love the idea of a toggle switch in the IGN circuit for compression testing so will incorporate that as well.
Any advice on the best place to pull a signal for my ammeter?
I had a heck of a time trying to piece together enough information from different sites about a basic wiring setup for something like a test stand so I want to post pics and a working schematic when I'm done. I was surprised at how little is out there about test stands... Its going to take a couple of weeks because I'm not home for a while but will be back with a working design for your community when I'm done.
Thanks again!
(This post was edited by 71Vette on Jan 28, 2018, 10:03 AM)
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71Vette
Novice
Jan 28, 2018, 8:47 AM
Post #7 of 14
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Re: Engine Test Stand Wiring Problem (Ign Switch)
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Tom, I like the idea of testing the IGN terminal with a test light when the key is switched from IGN to OFF to see if there is still power there and disconnecting the alternator feed to see if that kills it. The alternator is newly rebuilt and has worked properly in the car so its definitely my wiring and not the alternator's fault. Its a 10SI with internal regulator. Its a 2 post unit and I believe that #1 is F and #2 is R. The switch is a Pollack 31-610 and I'm not using the 4th post (ACC) for this application.
I'm going to try redirecting the #1 alternator feed to the relay circuit instead of the ignition switch to see if that solves my backfeed problem. Will report back!
Thanks again!
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Tom Greenleaf
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Jan 28, 2018, 9:14 AM
Post #8 of 14
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Re: Engine Test Stand Wiring Problem (Ign Switch)
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Just this point: "F" is field would charge more with stronger ohms to ground is why I said use a real light bulb not LED. If a real one with screws to a cover those you adjusted to be in range if new or failures just saw it was burned out all plain didn't charge to me. Testing my memory - these were new and it's your fault making me feel this old! Smile, Tom
Other: Was a '68 (first year that style) wires all burned up bad, carpet, seats wrecked but somehow fiberglass/paint was fine? A guy in town did only Vettes put a whole new wiring harness in the thing available then ~ 1974 or so every last bit of it! Car was all OE again like nothing ever happened, Tom
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71Vette
Novice
Jan 28, 2018, 10:00 AM
Post #9 of 14
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Re: Engine Test Stand Wiring Problem (Ign Switch)
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I believe the word you're looking for is "wise", Tom. I think we all know what happens when knowledge and experience is not passed from generation to generation so we appreciate you sharing your wisdom!
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Tom Greenleaf
Ultimate Carjunky
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Jan 28, 2018, 10:27 AM
Post #10 of 14
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Re: Engine Test Stand Wiring Problem (Ign Switch)
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I'm trying to apply "common" sense a thing that died long ago. How does it work and how should it work and why stuff. Then what improvement took out a step or became adjustable by Murphy's Law was misadjusted permanently when new so you are screwed to figure that out!
I still wonder about the dang keyed ignition switch itself. Have a box full or did. Some snap back some don't. Some you could take the key out in any position! Yes - so you didn't have to shut off a car to open a trunk and so on.
Some ACC positions were not "CC" rather just the first step "CW" and so on. Pull your hair out stuff sit and test what it does and in what position.
One more for now. You wired in electric fans and IDK if those are timed or not early ones stayed on long after you left, locked a car and shut down only with temp sensed it was cooled off enough. That relay may hold the surprise?
3 real American (so called) car makers each with their own quirks back to forever who did what first and was it a good move? Some wasn't! Tom
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71Vette
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Jan 28, 2018, 9:27 PM
Post #11 of 14
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Re: Engine Test Stand Wiring Problem (Ign Switch)
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Yes, I've also heard about the energy created by the spinning fan keeping the alternator energized after the key was shut off which is why I kept that fan circuit entirely isolated from the rest of the wiring harness. It has a temp sensor that sits just inside the rad intake that feeds an adjustable thermostatic control. Power is run directly from the battery to one side of the fan and the other side contains the control which terminates in the ground feed back directly to the battery. I flip the wires to the fan to change from pull to push depending on needs. No relays, no extra wiring, ultra simple plug and play fan control.
(This post was edited by 71Vette on Jan 29, 2018, 12:00 PM)
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Tom Greenleaf
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Jan 29, 2018, 12:00 AM
Post #12 of 14
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Re: Engine Test Stand Wiring Problem (Ign Switch)
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Wild thought with this on a rack on the floor is you shouldn't need the fans connected at all and take any feedback from them out totally. Use a good floor fan pointed at radiator should be fine there's no load on the engine just setting there running. Don't allow blades to turn if you do that, they could make power backwards! Tom
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Hammer Time
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Jan 29, 2018, 5:43 AM
Post #13 of 14
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Re: Engine Test Stand Wiring Problem (Ign Switch)
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Discretesignals is very knowledgeable in electrical circuits and you should follow his advice.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Discretesignals
Ultimate Carjunky
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Feb 20, 2018, 7:53 AM
Post #14 of 14
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Re: Engine Test Stand Wiring Schematic
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Very nice circuit you got there. Love the schematic. Great job!
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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