AUTOZONE??? Why? I can't imagine they'd have anything correct for an old Mercedes besides oil and light bulbs.
$130 bucks doens't seem right but I cant remember and my records are in California.
The silver box attached to the bracket further up in the dash closer to the speedo is not it. The preglow relay is not that big.
Look more towards the front (closer to the driver) and down (lower than the speedo) It should be connected by a 5 pin connector, also the pre glow relay will likely have some high amperage rating on it being it's part of the glow plug system.
Sorry I don't know where the fuse is..

Try fastlane for the part.

__________________
63 220S W111
76 300D W115
2013 VW JSW TDI M6

previously-
73 280 SEL 4.5
86 300E 5 speed
2010 VW Jetta TDI M6

Does it look like this?

http://63.89.49.212/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1CQ0J3JZ41RM0PV9T5&year=1976&make=MB&model=300-D-001&category=All&part=Preglow+Time+Relay

Ok I guess pictures are not going to work. at least today. I also know that starting fluid is not the healthiest thing for a motor. This one only needs the tinyiest whiff. You really know about it if you give it too much. Well I pulled the plug off the suspected relay. It has 6 pins plus a big alignment pin. ONly 5 of the six positions have contacts installed . So is the glow plug relay a 5 pin job. Any one know how to test it?
I gotta make the donut$$, now more this evening
thanks for all your help so far
mercedes hawker

Many thanks everyone. Craig thanks for the picture!!!! I believe this is the animal. I do have to get to work, so thanks and again more this evening. does anyone know the test procedure for the relay??
thanks
mercedes hawker

$130 sounds really fishy to me. If it is the case that you need to replace your relay just update the plugs all together. They work way better and if one goes out then one goes out....not all of them. Not to mention the whole kit is $40 cheaper than just the relay. You will need to get one more GP though as the kit only comes for the 4 cyl.

http://***************/search/productx.aspx?sid=ievynk45qyhmjb553oj1y0my&makeid=800016@Mercedes&modelid=1192913@240D&year=1974&cid=glow%20plug@glow%20plug&gid=7164@Glow%20Plug%20Kit

I post this as I didn't see it on Phil's site. Sorry bout the competition but just makes sense.

__________________
76 300D 130K "Stella" (Sold )
74 240D 299K (Donated to Highschool For Senior Project WVO)
83 300TDT 290K (My one and only)
Sanford, NC

Thanks to everyone especailly the link to the replacement unit with the cost. no one knows how to test the glow plug relay?. I just read a thread that said someone took theirs apart.
thanks again

Glow Plug Relay Question

there's some insight in that thread.

Craig's picture is the relay.

__________________
63 220S W111
76 300D W115
2013 VW JSW TDI M6

previously-
73 280 SEL 4.5
86 300E 5 speed
2010 VW Jetta TDI M6

Well the problem is located and bypassed. Special thanks to Joshhall reply #13, and craig reply #17. NO glow plug light no start The problem was the relay. I guess the test for the relay is to bypass pin 5 to 6 on the relay plug ( hinted at in the 1 year off '77 300d schematic in the haynes manual, and then verified first with a ohmmeter and a long test lead), and see what happens. For me turn on the key make the bypass , instant bright glow plug light wait 7seconds and start . Fired rite up and I pulled the jumper. Every thing seems good.
Again many thanks to all. Now on to the next problem.
Any one want to buy a 1976 mercedes 300D, it needs some lovin but here is quite a bit of car left.
I had to throw that in there ..... thanks again
Mercedes Hawker

Good to hear. I hope you find a good home for it.
I'll have to remember that trick.
Pin 6 is power coming in and pin 5 goes to the first glow plug in the series?
So what you did was directly wire pin 5 to 6 on harness, thus bypassing the timer of the relay? Where does the ohm meter come into play on that process?

Those haynes manuals work okay, they didn't change much in the way of electrical setup from 76 to 77.

__________________
63 220S W111
76 300D W115
2013 VW JSW TDI M6

previously-
73 280 SEL 4.5
86 300E 5 speed
2010 VW Jetta TDI M6

since the haynes manual was off by one year. I used the ohm meter to verifiy that the schematic was correct. so I checked for continuity between one of the pins and the battery + terminal ( would be power supply to the relay. Next I checked the other pin to verify that it was a direct connection to the #5 glow plug ( the output of the relay to the plugs). The jumper was installed in the connector plug that hooks onto the relay. It is almost like hot wiring a car as seen in the movies. YOu pull the plug from the relay and then just jump those two pins in the plug and you are in business. The puzzler comes in , ? How did the dashboard glow plug light get power during the bypass. on the schematic the dash light is on another pin of the relay seperate from output terminal????
PLEASE NOTE For those trying this at home please be careful to use a adequate wire size for the jump ( quite a bit of amperage there). Also remember to pull the jumper after the car starts. With the jumper installed the glow plugs are on all the time. from dead south Texas cold it only took about 5 seconds for the plugs to be hot enough to start the car.
For $130 I will probably install a high amperage momentary on switch to handle the glow plugs . I guess I did not need that part after all
thanks again for your help and the chat
have a good night
Mercedes hawker