Projects Stupid electrical question

I am working on wiring my project this past couple of weeks. We went to crank the engine over today and nothing. Gor out the test light and grounded it to the body and the entire engine is positive (the test light lights up anywhere I touch the engine) What could my issue be?

I took the fuze out going to the fuze out of the fuzible link where the main power to the fuze box hooks to the starter and the engine looses its positive power.

 

I had a similar problem. Cured it by grounding the battery to the frame, and installed a 1" braided copper ground strap from the frame to the engine block.

 

I still need to install a ground strap from the engine to the frame but with the entire engine having a positive power seems like I would fry the battery if I add a ground cable to the engine now with the entire thing having a positive charge.

 

If there is no ground to the engine, either with a cable or even a metal choke cable or anything like that, then yes, your test light will be acting as a ground through it's bulb.


To prove the theory: Take a small gauge wire and go from negative of the battery, to a good grounding part on the motor. Then the test light will not work like it did.

 

Unsound theory there... ground is ground regardless of a positive or negative ground system. You can do more damage without the ground strap in place.

Bob

 

First off, is your flying lead going to the battery negative? If it is, and your light is coming on when you touch the motor, you must be getting a positive from something on the motor, EG your starter. If that is the case, you have an internal problem in the starter. If you connect a ground strap to your block in this condition, yes you will get fireworks, as you will have a short circuit across the battery.

 

Another post where we're supposed to be detectives and have maybe 10% of the clues.

Bob

 

I had a no start problem with my truck after wiring it. Had 8 volts going to the motor. I did 2 things & 1 of them fixed the problem. This is on a Ford. I grounded the starter solenoid to the body & cleaned a little more where my battery ground wire bolted to the frame. Battery is under the floor on passenger side.

 

It could be that your body is positive. The way you are using your test light only tells you if there is a difference in potential, Not which side is positive. Test to the battery.

As an example, if your dome light is on it grounds to the body, but if the body doesn't have a good ground the current flows through your test light and it lights. You have to have a good ground on everything that needs to be grounded FIRST.

 

If you have your test light hooked to the positive post of the battery then the test light should light up any time you touch the engine, body or frame if everything is grounded properly.

 

Need a little more info. What engine? Where did you connect the ground cable from the battery to ? Dumb question , but you did run the + side of the battery to the post on the starter and the - side of the battery to ground, didn't you ?

Don

 

If you are testing with the ignition switch in the on position and the engine is not grounded then anything attached to the engine that has power going to it and gets its ground from the engine such as an electric choke or even an electric gauge sending unit will allow current to pass through it to the block.Your test light is completing the circuit allowing a path to ground. If it is happening with the ignition switch on the off position then you have something wired incorrectly of a defective component such as a starter solenoid. You can test each component with a ohm meter . You need a good ground going to the block in any case.

 

What other info would you like?

the engine is a SBC, The battery is in the trunk, the battery is grounded to the frame. I welded a boss into the frame and cleaned the face to bare metal before hooking up the cable. I did check the battery and it is hooked up where the - goes to ground to the frame and the + goes to the starter.

The circuit is completed with the ignition on or off at the ignition switch.


If I ground the starter, do I hook it to the stud that is on the main body of the starter?

 

I usually run a full sized ground strap from a bell-housing bolt to the frame, and another lighter one from the body to the frame.

 

You can never have to many grounds.some race cars i'v seen with battery in trunk, ground to the frame in back and still run a battery ground cable directly to the motor!

 

I am another in the add a ground cable from the engine to the chassis camp.You have to remember the engine is isolated from the chassis by rubber motor mounts.

 

Bad starter solenoid grounding to the solenoid case, then to the engine block?

Disconnect the starter power feed and check for continuity between the starter power post and the block. If that's not it, then it's got to be something else electrical on the vehicle...alternator/generator, ignition, something. Here's a piece of advice - connect your test light, then disconnect one electrical item at a time until the light goes out. When the light goes out, the last thing you disconnected had to have been the problem.

 

Spent a lot of time in the 12 volt industry , and a circuit will search for adequate ground any where in can find it , so the extra grounds are always a good thing , especially if you plan on a sound system , different ground voltages will cause all kinds of noise in your system also . That being said , it may be time to break out a meter and start testing continuity and find where the positive is entering the ground plane of the vehicle . removing the lead to the starter would be a good place to start imho

 

If you are using an alternator and the engine isn't grounded, it would light a test light. I don't know how you would avoid some type of connection between the engine and the frame. The shift linkage or throttle linkage usually grounds it. You need the best ground possible to the engine as the starter draws the most current in the system. The ground cable should connect directly to the engine from the battery. You also need good heavy grounds to the frame and body. Long cables need to be larger which is why manufacturers usually put the battery close to the engine

 

Don't over think this. If the motor and the body are not grounded to the frame then what you said happened will happen. Start there.

Remember: ground wires are suppost to be as short as possible, so running one all the way from the trunk would a waste of copper. Just buy good stuff, and ground the engine and the body well, and you wont have any problems

 

I went to the shop for about 20 minutes and messed with the car. took the fuze out of the wire that powers the fuse block to see if the body and frame were carying power or not. With the fuse out nothing was carying power. Placed the fuze back in and the body was still ground and the engine has power. Connected a wire from the frame to a bolt on the engine and the frame. Engine is no longer powered with the test light. Tomorrow nite I will go down there and place a ground strap to the engine and frame, and another strap from the body to the frame. Then I will see if everything else is wired correctly.


Thanks for the input guys.

 

You have just experianced what is know as "open circuit" voltage. No current flows, just the engine is floating and the 12V to the alternator and/or the regulator is seen by the tester. You would have seen the same thing with a VOM. The engine would not have cranked had you tried.

 

Copper is a much better conductor than steel. In race cars, we had to mount the battery inside the car and we used 2/0 welding cables to run both the positive and negative to the starter. Those who grounded to the roll cage and from the cage to the engine had hot start problems.

 

It took a month of head scratching before I came to realize these issues were cured by the above, in a recent build's starting problems. Agreed X2.

 

Your engine is mounted on rubber. It is isolated from the battery (no ground). That is why the starter does not work. When you connect your test light between the engine and battery ground, the test light is actually acting as a ground. It light up because of the current passing thru it.

I have had this happen intermittently, the engine would rock around and sometimes make a ground. Other times it would not. I finally clued in one night when the choke cable got red hot, melted in pieces and fell on the floor.

In your case check that the engine is grounded to the frame and the frame to the battery. Or, that the engine is grounded to the battery and the battery to the frame. Same difference.

 

Thanks for all the input guys. I got it fixed last nite. All I needed was to add the ground strap to the engine and all is good now. All accessories turn on and off with the ignition switch and the engine cranks over now.

Thanks again.

 

As many cars as we built you would think we have this down by now>>> o well we keep learning..

 

Some years back, I just dropped a motor into a new stock car, anxious as heck to get it fired. Did the bare minimum and disregarded the grounds. It started okay... started missing bad within a minute and the battery cables were as hot as hell.

Shut it down, looked around... Hmmmmm... no grounds. Ran a strap from the engine to the cage in the front, ran another from the battery in the trunk to the cage in the back. Made them from big (00?) battery cable with crimped lugs.

Bob

 

wait- you've got your tester on batt (-) and you're connecting it to the engine block, and it lights up?

Can you re-describe how you're testing this, and what's connected to where? battery, motor, tester, ignition, alternator?

 

The issue is resolved now. When the tester was connected to frame and touched the engine it lit up. Added ground strap to the engine to finish the circuit and everything is good now. As stated above the engine and trans are iso mounted so the electricity was looking for a ground somewhere to finish the circuit.