I recently purchased a 1985 300TD wagon. It was running great until last week. I started the car and the preglow light failed to come on. It started tis way a few times until it died on me. I took the battery down to have it tested, they charged it and said it was good. I then took the car down to have the alternator tested they said it was also good. On my way home from the shop the turn signals failed and came back from the dead, the windows were sluggish and the hazard lights failed and also came back. I got home and the car failed to start. The clock keeps perfect time! The interior light are all dim and when I use the turn signal a noise comes from under the dash. Please help so I don't get soaked at the shop.

Hi,

I would tend to start with the most basic things first, especially since it seems you have a ton of electrical problems all at once. It sounds like you have had the battery out already, but I would make sure both battery connections are clean and firmly tightened.

Then I would trace the negative lead from the battery to wherever it attaches to the frame and/or the engine. At this point I'd remove the ground and clean that connection completely with sandpaper.

Next I'd trace the positive lead and make sure it is firmly attached to wherever it goes.

Hopefully it will be one of these basic things. If not, come back and post what you did and have found so far, and we'll try to suggest more things to try.

Ken300D

I cleaned all the terminals, and took the battery down to be charged. They said the battery was bad so I purchased a new one. The cars started right up, but the preglow light on the dash still didn't come on. I then drove the car down to get the alternator checked and it was good. I have a Haynes manual and it says that if the preglow light fails to come on it can be in the instrument panel or the in the preglow relay. Is this a common problem?

So the rest of your other electrical problems are gone (besides the pre-glow light)?

Great. Well, the failure of the pre-glow light to come on is a common issue with diesels, and it typically falls in the maintenance category.

As you know, your car uses glow plugs to start the car when cold. The dash light is an indication that this system is functioning. If the dash light is not coming on, by far the most likely issue is a bad glow plug. These cost around $11 each at good prices. (Hint: Get only Bosch replacements.)

Beyond the typical glow plug replacement, you can have a bad glow plug relay or a glow plug fuse (an 80-amp job that looks just like a flat strip). The glow plug relay is quite expensive.

Use the search function on this site to search on glow plugs, and you should find some simple testing procedures. Fortunately on your car, they are "relatively" easy to test and replace.

Also, on the assumption that the problem is just one or two bad glow plugs, you should continue to "pre-heat" the car for 10-15 seconds after you turn the key to ON before starting. This lets the remaining good glow plugs operate as intended and will allow the car to start sufficiently to get you going.

Ken300D

I checked all the glow plugs like it said in my trusty Haynes manual. It said to put the ohmmeter on the 200 scale. Well mine only has one scale, the 1K scale. So I tested each glow plug, and I got readings in the 100-200 range for all the plugs. So I guess all the plugs are bad? Is it common for all the glow plugs to go bad at once? Is it a possibility the preglow relay had something to do with all the bad plugs? Right no the car will not start (but cranks over). I'm guessing because of the glow plugs. No new electrical problems. They were all cleared up with the new battery.

I think the Haynes manual shows only the old style glow plugs (connected in series), therefore, the test method does not apply to your car. The plug should be around 0.9 ohms. It may not possible to read this low resistance if you use the 1K range. In some cases, a glow plug with 0.9 ohms can still give you problems.

Since you were able to start the car with the glow light out, the 80A fuse should be still good. You can buy a digit meter for as low as $6 and it can be used to check the glow plug.

If you are unable to verify the glow plugs, just change them. As Ken300D said, they are cheap. You may find a plug for less than $11. I heard that some people found half of the plug broken inside the engine when they removed the old one. You may find carbon deposit inside too. If you change the plugs regularly (clean the hole with a glow plug reamer if necessary), you may save yourself trouble later, especially if you are living in a very cold area.

Happy Holidays!

David

Fixed all my problems with a new (used) glow plug relay for $75. My car runs great again!