Starter turns when key out of ignition

[74M35A2]

That is a lawn mower relay. OK to use if not carrying more than starter solenoid current.

 

[Paycheck]

So when I towed the rig home I pulled both alt,starter &relay for testing found bad realay and bad alt on passenger side replaced alt and relay the following pictures is the after math t thought I wired batt up wrong turned out the new alt was not a isolated ground unit please verify your parts I did with the auto parts store but he was wrong


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[Paycheck]

So when I towed the rig home I pulled both alt,starter &relay for testing found bad realay and bad alt on passenger side replaced alt and relay the following pictures is the after math t thought I wired batt up wrong turned out the new alt was not a isolated ground unit please verify your parts I did with the auto parts store but he was wrong


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[Paycheck]

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[Paycheck]

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[Paycheck]

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[The FLU farm]

Had an auto electrician walk me through testin g everything it appears the alternator I replaced is the culprit the parts store sold me a non isolated ground alternator auto parts store is paying for all the damages I just need to pony up for the new alternator I appreciate everyone's help thank you

There has to be more to it than using the wrong kind of alternator. At least I can't quite picture how it could make the starter activate.
Collateral damage from using the wrong alternator, perhaps, possibly combined with hooking up the batteries wrong? Getting 12 volts (and high amps) to the starter, in the process "welding" the starter relay and/or solenoid on the starter?

 

[Paycheck]

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[The FLU farm]

When creating that kind of sparking, repeatedly, you're better off not having functional charging. Glad you didn't blow up a battery and get sprayed with acid.

 

[Paycheck]

In the beginning the starter would not stop turning causing batteries to drain out,I pulled both batt for charging,pulled started assuming solenoid was stuck after test came back bad alt passenger side I purchased a new alt after putting everything to get her I assumed I had batteries hooked up wrong. Please forgive me I have been on several forums attempting to figure this problem out, all is done assuming I replace with isolated ground alternator everything should be fine. I post these so everyone seeing knows to be carful when replacing alt this was a Long process to diagnose this problem


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[Paycheck]

Now new dog head relay installed and waiting for new alt
Didn't think to check doghead relay in beginning from what I've read these things are in fallible


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[Jbulach]

Trouble shooting doesn't have to be performed "live". Using a 9 Volt battery is often enough when it's easier to have voltage in a circuit than measuring resistance...

Best bet is using resistance, to start isolating wires, when the starter is stuck engaged and lots of melted wires.

 

[doghead]

Nothing is infallible, but that relay is very very dependable(depending on manufacturer and manufacturers quality).

And for what it's worth, it's a relay. Not a lawnmower relay, not a ford relay, just simply a relay. It's used in frieghtliner trucks, trains, busses, and maybe even the space shuttle.

It's a relay rated for 200 amps, used in place of one that was rated for 40 amps, and mechanically it is designed different that the original.

It is much more reliable and better designed for this application than the OEM relay.

Back to the issue...

 

[Paycheck]

Nothing is infallible, but that relay is very very dependable(depending on manufacturer and manufacturers quality).

And for what it's worth, it's a relay. Not a lawnmower relay, not a ford relay, just simply a relay. It's used in frieghtliner trucks, trains, busses, and maybe even the space shuttle.

It's a relay.

It is much more reliable and better designed for this application than the OEM relay.

Back to the issue...

I can definitely say this has been a learning experience I have learned a lot about the 24v system in the last few days I appreciate all the help and knowledge giving I have learned a lot I'll be adding liquid electric tape to the relay hoping to extend life


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[Jbulach]

...I'll be adding liquid electric tape to the relay hoping to extend life


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FYI, those should be heat shrink connectors. Hit them lightly with a heat gun, they are quite helpful for strain relief as well.

 

[cucvrus]

I still like the plug and play relays. Just never had a trouble with them. 22 years and still going. No reply needed. Do as you wish. I am convinced I have a good setup. Have I replaced a few relays? Yes. Do all things fail? Always have and always will. I have a very nice special relay I received and have been using. Plugged in and no exposed power points on a steel dash and cab area. Thank you my friend for these wonderful cube relays. I like them. I like them a lot. I owe you one.

 

[Paycheck]

Battery shut off is next on the list if relay fails I can save battery drain


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[cucvrus]

Or just reach up and unplug the relay. End of story. It can be mounted 2 ways. Plug towards driver. Plug towards firewall. Firewall mounted plug unplugs with a gentle tug. All over. The END. Roll the film credits. Mic drop.

 

[doghead]

A battery disconnect poses several problems with these trucks during a starter run-on. I would not do it.

 

[Rvitko]

Having given serious thought to a battery cut off, it is more complicated than is practical, a 24V cut off is a big switch that is not easily mounted and not easily protected from shorts and just cutting off 12V during a run on can cause worse or further damage I have heard. When my run on happened the batteries shot out molten lead and acid, and it wasn't exactly like I wanted to be messing around with a shut off at the time and running it into the cab meant further potential failures from a cable rubbing through, being too long and higher resistance or a short across the terminals. In the end, I just rebuilt everything back to new, I already had done the doghead mod and I upgraded all the battery cables to one gauge up. It was a pain and time consuming, but now I just pay attention to the battery gauge and if it is in the yellow and not just when the glow plugs are running, I wouldn't turn the key. My issue was a fused solenoid contact on the starter and not the relay and my fatal flaw was keeping old crappy batteries because I wanted to do batteries last after I had everything else fixed so I would not potentially ruin batteries with a lot of down time on a vehicle I was working on. I would have been money ahead changing the batteries twice in hindsight.