I have an '85 300D turbo California version. The tachometer has been inoperative since I have owned it. I found a burned fuse located behind the glove box. When I replaced it with a good one, the tach worked but to my surprise the car would not shift out of 1st gear. I had no idea that the tach could affect the operation of the transmission. I removed the fuse and the trans works fine again but the tach doesn't work again. There is nothing in my factory shop manuals about the transmission nor does my ATSG transmission manual offer any help. Does anyone have an idea what is going on here? Thanks in advance for any suggestions you may have.

There is NO electrical connection TO the transmission that I know of except the kickdown switch. I is possible that the fuse energizes SOMETHING that is incorrectly coupled (or shorted) to the kickdown circuit and that would prevent shifting until the engine reached the redline (~5100) in each gear before shifting.

Marshall

That sounds like a possibilty. The problem is that there is no separate wiring diagram for the California model or at least nothing that I have shows anything. I wish there was some way to diagnose this problem by seeing what circuits may be involved. Until then I'll have to live with the inop tach. Everything else seems to work fine on this car with over 217K miles, 5K of which were put on it by me since March when I bought the car.

You probably knocked a vacuum line off. Check out the vacuum line going to the tranny and insure everything is secure.

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Jim

It'd be great if it was something as simple. Everything is hooked up.

Seems to me that there is an electrical switch under the throttle pedal, at least I remember it being there on my 78 300D. When the pedal is pressed to the floor it will cause the trans to downshift. Could there be something like that on later diesels?
Might look. It would be under the pedal.

Remove the fuse. If it is a strange electrical problem, it should shift good again. If it still doesn't shift, either you caused some collateral damage or it is just a coincidence.

Jerry

That's what I immediately did. I figured that it should work normally again after removing the fuse which it did. But now I have to figure out what is causing this strange problem. The CA model has an EGR system which is somehow linked to the tachometer circuit. I was wondering where I could get a wiring diagram for the CA model for 1985. I might be able to solve this unusual problem once and for all. It would be nice to have a tach that works.