No need its been done already.

Wiring diagram:

http://www.peachparts.com/shopforum/...8&d=1176742781


RPM Sensor check:

http://www.peachparts.com/shopforum/...3&d=1185146654

There is no tach amps on '84 or '85 300D and 300sd models. See diagram above.

Good job, thanks.

Awesome guys. Thanks for the info. Now that I have electricity again at my house and things cleaned up from the recent Indiana storms, I'll hopefully be able to get back to my tach/ac problems.

I think my next step is unearthing the EGR control unit and seeing what the contacts and solder points look like. A new (used) OVP relay didn't do the trick unfortunately.

my tach came back to life with a junk yard egr computer. mine had terribly corroded connections, i think it got water from leaky windshield on it. What does jimmy want ? Pin count on egr computer or connector socket, i thought the socket/plug had female, and the egr computer had male pins, I didnt look too close, but i can count whatever you want for me to count

Hey John,
Good job on getting the tach to work!! Nice.
I wanted to know how many pins were coming off the connector from the car to the EGR computer. I.E., how many pins in the wiring harness. Mine were also corroded green, and I'm hoping one didn't pull off in the old EGR computer. I supposedly got a good used one, but it didn't work. :(

**edit**
Uh oh, I'm out in the garage holding the old EGR computer and it appears to have male appendages. :eek: Guess I need to pull out the one in the car and refresh my memory as to what my main issue there was. Doh!

Tach Fixed!
 

Well, I just got my tach working too. It also was corrosion in the EGR Control Module connector. I pulled off the socket and nasty greenish white water came out! You can see the mess on the door sill in one of the pictures. I think the water in mine came from a cracked hose for the AC drain.

I blew all the water out of the connections with a compressor, cleaned up the pins with a bit of fine sandpaper, blew clean again, applied a bunch of dielectric grease, reconnected the module, and voila - working tach. Now I just need to repair the crack in the little hose.

Sorry, I didn't think to count the little connectors in the harness before I filled it with grease, now I can't really tell which holes have connectors in them. My best guess is that they matched the circuit diagram above.

OK, I have found my problem I think. In the schematic above, item #80 [control unit], top row, pin #3 from the right is broken off my old EGR computer, and the female pin looks to be broken off from the car connector. I'm heading out to see if I can punch that pin out. Will report back and snap a few pics.

**edit**
Oh dear! 4 broken wires so far!!! At the pins inside the connector. One pin missing completely. I am going to hope that somebody can find one of these connectors at the salvage yard and cut it out for me about 1/2 foot up from the connector. Then I can splice into my wiring harness.
I just came in for a paper clip to try and use as a pin punch and thought I would update.
It ain't pretty......:eek:

Well there isn't a whole lotta wondering now why my tach wasn't working on my '85 wagon. 7 of the 14 wires in my EGR connector are broken off at the pins. It only started off with 4 broken, but I just touched 3 others and off they came. Really deteriorated in there! Dang!
Here is the EGR computer module:

http://i29.photobucket.com/albums/c2...ompfrm85-1.jpg

Here is the old and new one up next to each other. The newer one on the right has much cleaner pins. Actually the one on the left has a broken pin, but it isn't used.

http://i29.photobucket.com/albums/c2...85Stuff131.jpg

So, at the connector I first had to peel back the rubber cover, which of course split. Also had to remove 2 screws at that end:

http://i29.photobucket.com/albums/c2...85Stuff139.jpg
http://i29.photobucket.com/albums/c2...85Stuff137.jpg

Then one screw out of the top:

http://i29.photobucket.com/albums/c2...85Stuff136.jpg

Here is a good look at the issues going on in there, and it wasn't hard to find:

http://i29.photobucket.com/albums/c2...85Stuff142.jpg

http://i29.photobucket.com/albums/c2...85Stuff141.jpg

http://i29.photobucket.com/albums/c2...85Stuff140.jpg

I tried for a half hour to punch one of the pins out of the connector and just couldn't get it done. I was gonna try and match it up somewhere, but I think my best bet is still to hope somebody can find an '85 in the salvage yard and cut out the connector.

Anyone?
Anyone?

:smart:

when i scored the egr computer i cut off the end bit off with it, dont recall what i did with it, i doubt i threw it out. let me go look

found it, send me a pm with your address, ill mail it out to you.

YOU are the man!! PM on the way.........

:dancefool

Many many thanks to Johninva!!! What a good dude. Not only had the foresight to cut out that wiring connector, but sent it to me in less than a week. Awesome!

http://i29.photobucket.com/albums/c2...85Stuff160.jpg

Got it today and you can bet I stayed out in the garage tonight until I got it installed.

First thing is first. Had to get the fans pointed in all the right directions. I had 5 and one ceiling fan going out there. Kept the mosquitoes away too.

http://i29.photobucket.com/albums/c2...85Stuff157.jpg

First step was to cut the old one out. It just seemed weird to cut all those wires.

http://i29.photobucket.com/albums/c2...85Stuff161.jpg

http://i29.photobucket.com/albums/c2...85Stuff162.jpg

I went ahead and did the wire twist/solder thing. I'm just not a big butt splice dude.

http://i29.photobucket.com/albums/c2...85Stuff163.jpg

http://i29.photobucket.com/albums/c2...85Stuff164.jpg

http://i29.photobucket.com/albums/c2...85Stuff165.jpg

My Harbor Freight soldering iron burned out with one wire remaining. Had to go to a backup that barely got hot enough.
Got it finished and secured and connected back to the EGR computer.


http://i29.photobucket.com/albums/c2...85Stuff173.jpg

The moment of truth. I glowed the plugs, turned the key and the ole wagon fired to life. And I watched that limp arse needle stay right there at 0 where it has always been. Doh!! I gave it about half pedal to raise rpm's and I'll be darn if that thing didn't snap out of its familiar location and has been working every since. I guess it sat in one place so long that it was a little stuck.

http://i29.photobucket.com/albums/c2...85Stuff167.jpg

http://i29.photobucket.com/albums/c2...85Stuff168.jpg

I drove around the block and I'm mesmerized by the tach now......

**edit**
BTW, I also hooked up my ugly little original EGR computer and the tach works with it also. So that was $50 bucks I didn't need to spend on that, plus I think I bought a couple of OVP relays. Never did buy the tach pickup as the voltage pulses from it were correct.

That's awesome. I've been waiting for a happy ending on this one. I know I was so pleased to get mine working again.

Now that that's done, you have a chance at working A/C too!

I got the AC working shortly after I bought the car 3 years ago. You just have to jumper the Klima relay as follows:

http://i29.photobucket.com/albums/c2...985/Klima3.jpg