Bypassed start wiring with separate push button ignition switch

TERMAXCO

MEMBER
1995 JEEP GRAND CHEROKEE
6 CYL
4WD
AUTOMATIC
110,000 MILES

On our vehicle listed above 2 and 4 wheel drive: It began
starting intermittently and cranking slowly after multiple switch
attempts. Battery is good, and I bench tested pretty new starter and solenoid and they worked fine.

So, I just up and bypassed start wiring with separate push button
ignition switch and wiring without a relay etc.

It's just battery, solenoid (to starter) and ignition switch (no relay).

Battery cable runs from battery to input terminal on solenoid. From that terminal with the battery, cable, ran 8-gauge wire to push button ignition switch, and from switch back to small terminal on solenoid. Wires are some longer than they need to be.

Still intermittent as before. After multiple switch tries with a 'very'
slight click, it would finally hit and start good. After a few tries and
starts like this, the click stopped and both the ignition switch and
solenoid burnt up with lots of smoke from both till I unhooked the
battery. The switch burnt closed, and the solenoid seems to be burnt open.

Any ideas what I did wrong? Thanks

5 Replies

AL514

MECHANIC
4,692 POSTS

Hello, the starter circuit pulls a huge number of amps, just because the starter bench tested okay doesn't mean it's good. On the bench there's no load on the starter, but when it has to turn over an engine it's a totally different story. When I do a relative compression test, which I use the starter wire going to the battery I use an amp clamp that's rated for 600 amps. So, you can see what happened. The starter was just in need of replacement.
You might want to turn the engine over by hand as well using a socket and large breaker bar, just to be sure your engine turns over smoothly. Just to be safe.

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Thursday, October 28th, 2021 AT 2:39 PM

TERMAXCO

MEMBER
54 POSTS

The engine turns over fine. The starter and solenoid are relatively new, and the solenoid benched okay; and, on the car when the solenoid did finally engage the starter for a few starts, the starter turned the engine over real fast and strong. When the starter didn't turn the flywheel on multiple switch attempts it was not engaging into it at all. The clicks were very slight at the switch (until it burned closed).

So, I was concerned about either something wired wrong or the ignition switch and solenoid engaging switch getting too many amps straight from the battery without a reducing relay and burning both up before they could work good; and that, perhaps today's switches are designed weak to run only with reducing relays. But then, why did they intermittently work good at all then? If this is a concern, how should it all be done?

If this is not a concern and the new wiring is OK in all respects, since the starting system is now separated from everything else and the battery is good - is it correct that there is only the switch (that burnt up closed), solenoid (that burnt up open) and starter left to choose from as far the problem?

If so, since the starter did work each time, it was actually engaged into the flywheel does that eliminate it as causing the other parts to burn up; or, which one - the switch or solenoid - sounds most likely? Or other?

Thanks again!

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Friday, October 29th, 2021 AT 9:56 AM

AL514

MECHANIC
4,692 POSTS

I'll get you the wiring diagrams for the whole circuit. What sub-model is this? Laredo, Limited, Orvis, or SE?
The diagrams for the starter circuit are below, I would use a multimeter if you have one for just checking that you have a full 12-volts on the starter wires. and check the connectors at the starter too, make sure they're not corroded or rusted up, a bad connection will act as resistance on the circuit and produce heat. Overheating the relay, the solenoid, any connections. Since it draws such heavy current during start up, especially cold start up, you can see how this would cause problems. It's never a good idea to bypass circuits. They're designed the way they are for a reason. And yes, the relay is to energize a high current circuit with a low current circuit. Even a new starter can be bad, they are just remanufactured parts. I've gotten bad parts that were new countless times.

https://www.2carpros.com/articles/how-to-check-wiring

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

https://www.2carpros.com/articles/how-to-use-a-voltmeter

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Friday, October 29th, 2021 AT 10:34 AM

TERMAXCO

MEMBER
54 POSTS

It's a 95 Limited. But I have bypassed the entire wiring for the start system (the other power of/by the car wiring circuit, such as to the coil etc, is done through another switch which all works).

So, I have:

The positive battery cable to the solenoid and an 8-gauge wire from the battery to the ignition switch and.
An 8-gauge wire back to the solenoid small terminal.
(The solenoid to starter - starter grounded to engine to frame back to battery ground).
Nothing else is involved unless I am mistaken.

I just do not know how this is either not workable or otherwise, why it did not start the engine on every try and then why it burnt up and smoked the ignition switch and the solenoid. Can you suggest what might be going on?

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Friday, October 29th, 2021 AT 11:05 AM

AL514

MECHANIC
4,692 POSTS

It's probably an issue with the ignition switch, even a starter solenoid pulls current, it's not your average relay, it's probably too much current threw the ignition switch, bypassing anything like this just isn't a good idea, engineers design these systems, they know exactly how much current is flowing and where it's all going. Plus, the circuit you're using as a bypass doesn't sound fused, so it has no protection from over current situations. There are other components drawing current off that circuit. I would just put it back to stock, and find out what's really happening, you should see how much "inrush" current there is on a starter motor on a lab scope. Its huge.