C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

Help-What is this plug?

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Old Nov 30, 2025 | 11:13 PM
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Default Help-What is this plug?

Can't tell where it goes...driver's side
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Old Nov 30, 2025 | 11:19 PM
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It's your brake warning light switch.

It's supposed to plug into your master cylinder, but it looks like you don't have the right connection on the master cylinder itself. (that white part that's threaded into the master cylinder just above where your brake lines are threaded into it..it's not right.)

Or maybe it is right and the top part of it is maybe broken off. I can't really tell from the photo.

As an aside, you might update your profile to reflect what year C4 we're working with. Or just mention it.

If it ends up that the switch is broken at the top where the pigtail connects, those switches are unobtanium unless you buy a new or used master cylinder now. And a lot of times the new ones don't even come with the switch installed any more because they guess you're just gonna swap out the one from the old master cylinder and thread it into the new one.


Last edited by Natty C; Nov 30, 2025 at 11:30 PM.
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Old Nov 30, 2025 | 11:32 PM
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It actually looks like someone plugged the threads on the master with something. After zooming in on the photo, it doesn't look like a broken OEM switch.

It should look like this...


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Old Nov 30, 2025 | 11:38 PM
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By the way, that pigtail is pretty much unobtanium, too.

So best to wrap it up and tuck it away some place in there until you get the switch resolved so as not to get caught up in your steering or whatever and get destroyed. Becuse it will if you don't.


Last edited by Natty C; Dec 1, 2025 at 11:45 AM.
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Old Dec 1, 2025 | 12:15 AM
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Originally Posted by Natty C
It's your brake warning light switch.

It's supposed to plug into your master cylinder, but it looks like you don't have the right connection on the master cylinder itself. (that white part that's threaded into the master cylinder just above where your brake lines are threaded into it..it's not right.)

Or maybe it is right and the top part of it is maybe broken off. I can't really tell from the photo.

As an aside, you might update your profile to reflect what year C4 we're working with. Or just mention it.

If it ends up that the switch is broken at the top where the pigtail connects, those switches are unobtanium unless you buy a new or used master cylinder now. And a lot of times the new ones don't even come with the switch installed any more because they guess you're just gonna swap out the one from the old master cylinder and thread it into the new one.
Thx. Is there an easy way to update so everyone knows my car? Thx for the info
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Old Dec 1, 2025 | 12:40 AM
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Originally Posted by Stoddard Garage
Thx. Is there an easy way to update so everyone knows my car? Thx for the info
I think there is some place in your profile settings.

I've never messed with it. But I know you can because i've seen others have done it whenever I've looked at their profile.

I usually just say the year in the OP.


Last edited by Natty C; Dec 1, 2025 at 02:12 AM. Reason: Typos...
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Old Dec 1, 2025 | 04:27 AM
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Originally Posted by Stoddard Garage
Can't tell where it goes...driver's side
You should also do yourself a favor and get that alternator positive rear stud covered with a plastic cap or rubber boot of some sort. Also, possibly consider redoing the ring terminal connector (or at least cover the gap between the red wire and yellow barrel with electrical tape)! If any metal tool ever touches that, you'll have some good arc welding/sparks flying everywhere going on!!! Nobody wants to have a crispy corvette👍
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Old Dec 1, 2025 | 09:42 PM
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Originally Posted by '78CorvetteS.A.
You should also do yourself a favor and get that alternator positive rear stud covered with a plastic cap or rubber boot of some sort. Also, possibly consider redoing the ring terminal connector (or at least cover the gap between the red wire and yellow barrel with electrical tape)! If any metal tool ever touches that, you'll have some good arc welding/sparks flying everywhere going on!!! Nobody wants to have a crispy corvette👍
The way the picture is cropped, it looks like he's re-routed the BAT wire along the LH side of the engine compartment to the jump start block.

That's the way that it should be done if anyone ever has to replace that wire.
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Old Dec 1, 2025 | 09:48 PM
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Thank you everyone for the insights!!!
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