Mystery Plug
 

Hello, back again with another question. I saw this six pin plug under my hood on drivers side. I attached pictures so hopefully they show. After googling it seems to be a OBD1 plug?

Has anyone ever plugged an adapter into this?
I plan to turn truck on a test to see if anything in the plug has voltage tomorrow. It would be nice if the adapter I found could plug into this then the OBD2 side would feed it into a small screen that reads RPM and things.

Thanks!
https://cimg5.ibsrv.net/gimg/www.die...ef27a18cc.jpeg
https://cimg6.ibsrv.net/gimg/www.die...ee25abe16.jpeg

That is the diagnostic port it's pre obd1 so there are no modern obd1 and obd2 scanners available that can read the data outputs it would be like trying to get a modern laptop to play nice with a IBM 5100. Here is a list of data outputs you could pull if you had a vintage scanner, engine RPM, preheater status, coolant temp on the autos, cruise control status, vehicle speed, intake air temp, throttle position on the autos. If you just want a rpm gauge your easiest options are a magnetic tachometer pickup on the crank pulley or use the w terminal on the back of the alternator here's a video on how to do that not my video. One of my trucks has the w terminal tachometer and another one has a magnetic flywheel tachometer which is similar to the magnetic crank pulley tachometer.

Morning and thanks for the response. Here is the adapter I found plug looks the same as the vintage one. My truck used to be an automatic but had a NV5600 swapped in so nothing from the pin for the auto stuff will work Ofcourse, but what about the rpm speed and such ? All that should still work if this plug worked ?
https://cimg5.ibsrv.net/gimg/www.die...6089a4d1e9.png

One thing you should do is fill out your edit signature area in your profile so it is easier to help diagnose the problems with your truck. As Delco stated there will be nothing there to read.

The diagnostic plug tach signal has to be interpreted by a scanner so you cannot pull a tach signal from the diagnostic port, but under the dash should be a factory tach plug it's a black four prong plug with Black, Orange, Black, Greay/lt. blue wires i think isspro still makes a tach for these trucks https://www.isspro.com/aftermarket/r8503.html there is also a company called design technology that makes a product called the diesel tiny tach part # DTL-6 that works by reading injector pulses. Here are some threads on the factory plug and isspro tach https://www.dieseltruckresource.com/...9/#post2352358 and https://www.dieseltruckresource.com/...iagram-185725/

Since I seem to remember the OP has a '92/'93 that Isspro tach that allows you to plug in to the factory dash plug and use the crank position sensor you already have - seems like the easiest way to go.
The price is pretty decent to. Way cheaper than you will likely find a factory tach, if you can find one.

ok, filled it out I believe. Delco I thought said RPM could be read from that plug ?

As i said in the post above the rpm can only be read through the diagnostic port with a vintage scanner there is no magnetic pulses coming through that port only data bits. Carefully read my post above, there is a factory tach plug under the dashboard that you can pull a magnetic tach signal from.

ahh my apologies for reading that incorrectly. Regarding the plug under the dash what does it look like ? I thought only 92’ and 93’ had the tach plug.

91.5 intercooled trucks also had the tach plug under the dash, although sometimes on a 91.5 the magnetic sensor on the crank pulley was omitted then you will have to pick one of the custom options i listed above. Make sure you check around your front crank pulley for a magnetic tach sensor if it isn't there then you are out of luck on factory tach signal options.
here's is a pic of the plug under the dash
https://cimg7.ibsrv.net/gimg/www.die...909bea2c92.jpg

When I talk about 1st gen trucks I usually break it down to '89-'90 and '92-'93. Otherwise I feel like I could be confusing people, more than necessary.

I usually leave out the '91's - as the '91.0 and the '91.5 are so different and a lot of stuff changed over that year.
There are some things that make the 91.5 different from even the '92-'93...Like the engine bay harness which has a PCM for the first time, yet still has the voltage regulator on the firewall, like the earlier '89-'90s.
The '92/'93 have a PCM, but with the VR built into it.

When you own a '91 and you are working on it you need to pay extra attention when hunting down parts. When buying parts for my '91.0 at say NAPA, I just tell them I need parts of a '90 as they have a hard enough time trying to work their computer to find the right part #.

No, you didn't, go to your pic at the top of the page and click on your name next to it you should see this
https://cimg7.ibsrv.net/gimg/www.die...d099e28fa6.jpg
Click on edit your sig, then you should see the next pic fill it out where it says edit sig then click save changes then it will show anytime you post.
https://cimg3.ibsrv.net/gimg/www.die...ad3430381f.jpg
Hope this helps.

thanks! I’ll take a look and if not I’ll do the alternator method.

Worth noting,…
Just listing your truck as a ‘91, makes more questions than answers them…to the guys here that are trying to help you.

As I said earlier the ‘91 is a very tough year to get the right information on or part for.

’91.0 or ‘91.5 charges a ton of stuff on a Dodge Cummins truck.

Just a short list of parts I have seen that vary in that one model year.
Auto transmissions, motors, injection pumps and lines, injectors, throttle brackets, power steering/ vacuum pumps, radiators, fan shrouds, fan pulley and hub, wiring, voltage regulators / PCM, steering wheel, turbos, intake horn, A/C pump and system, axle options /gearing, locking hubs, driveshafts, rear leafs springs, rear lift blocks, core support……A LOT OF STUFF.

On the tread you started a few days ago called "Turbo Flutter" you said you have a '93. Now you seem to list your truck as a '91.

Going to be hard to get you good info....When we are given that sort of info to work with.
"Mystery Plug" indeed.