1979 300D.
Some where along the life of this fine automobile somebody added a push button switch for the glow plugs. Well last night the switch hung (closed) after starting and I had the hood up playing with the mightyvac and noticed it before it caught the car on fire. So this weekend (along with chasing down the vacuum leaks) I am going to try and repair the original GP system. I removed all the added wiring and switch, because it was not fused hooked straight to the battery, and just asking for trouble. I searched and read all I could find on the GP's and have a few questions. Is the actual glow plug relay on this car located on the left inner fender?(if not then where is it) Is the big flat fuse located on the firewall engine side?(if not then where is it)

Can the flat fuse be bought at normal parts store or is this a dealer only item?

What is the procedure for checking the GP relay?

Thanks for the information.

Johnboy

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79 300D
94 F-350 PSD
00 Excursion PSD
71 Karman Ghia (only gasser in the bunch)
2002 Club Car Golf Cart 48V 8" lift

Okay so I figured out why the PPO put in the push button switch, the blade fuse was blown. I hooked my fluke meter to the incoming side of the holder and 12V key on until I hit the starter and let go then voltage goes to 0. Is the fuse something available at parts store or MB dealer only?
What is the part #?

Thanks
Johnboy

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79 300D
94 F-350 PSD
00 Excursion PSD
71 Karman Ghia (only gasser in the bunch)
2002 Club Car Golf Cart 48V 8" lift

The fuse for the relay is called a "strip fuse" and you can get it from your dealer or an online parts store like our Fastlane. Your car probably has the serial glow plugs and I'm not sure what amperage you need. For the later pencil style glow plugs (1980 and later) an 80-amp fuse is needed and that's probably the one you want. Yes the relay is on the left inner fender.

The way I'd check for proper operation of the relay is to turn it on with the key and listen for a click. The click means the relay has cut out and this shouldn't happen at least until 20 seconds after turning it on. Second, immediately after shutting off the relay, make sure all glow plugs have been heated, either by looking at them through the injector holes, or by testing their resistance through the relay connector (the connector that supplies current to the glow plugs). If a glow plug has been heated, it's resistance will be high but dropping as it's cooling off. This way you'll be testing the glow plugs as well.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

Thanks DA, I am thinking the Relay is good, because with the key turned on I am getting 12 Volts to the hot side of the Strip Fuse and after cranking the car and releasing key back to the run position it goes to 0 volts. I am assuming that to restart the glow plug cycle one has to turn the key to the off position and then turn the key back to the on position, is that corrrect?

I will check with the dealer and see if they have any in stock.

Thanks

Johnboy

__________________
79 300D
94 F-350 PSD
00 Excursion PSD
71 Karman Ghia (only gasser in the bunch)
2002 Club Car Golf Cart 48V 8" lift

Not a problem. Yes you have to turn the key completely to the off position to restart the glow cycle. The ignition lock should prevent you from doing it any other way. Hopefully you don't have a short circuit somewhere which is what would blow the fuse in the first place. You might want to get at least 2 fuses just in case. If the first one blows you'll want to examine the glow plugs for a short circuit.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

Since there is not a MB dealer in the greater Godley Metroplex, I did a little improvising! I went and bought a 60 AMP fuseable link, basically a strip fuse with little plastic housing over the fuse part. I removed the fuse holder from the car and drilled mounting holes in the fuseable link to match the MB holder. After reinstalling the holder and hooking power back up everything is functioning properly. I cycled the GP's probably 20 times yesterday while working on various vacuum problems. The fuseable link is rated 10 amps higher than stock, but I do believe that if a direct short was to occur that the fuse would blow. I wil pick up a few of the stock strip when I get a chance. As well I am happy to report that my vacuum system is now operating and that the MB will die when the key is switched off, the A/C is working, door locks all working, fuel door latch working, trunk latch working!

I had a productive day yesterday! I sill need to figure out why the electric fan is not comming on with the A/C. I have jumped the pressure switch, and still I am not getting power to the fan. The fan works when connected to 12V. I may just pick up a relay and have the fan come on with the key in the on position. or via a switch. I live in TX, so it is hot most of the time, therefore I do not believe that the fan running would hurt anything.

Hopefully the Benz will allow me to park my dually here shortly and provide a reliable means of daily transportation!


Johnboy

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79 300D
94 F-350 PSD
00 Excursion PSD
71 Karman Ghia (only gasser in the bunch)
2002 Club Car Golf Cart 48V 8" lift

Having the fan run all the time might get annoying unless you don't mind the noise. It's not supposed to come on immediately after turning on the AC. From my understanding of it, it will come on either because of high refrigerant pressure or high coolant temperature.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

I will do some more research and see, I just did not want to get in a traffic jam and have it get hot on me. Noise wise well I would like it quite but my current driver has 4" Straight Pipe exiting in front of the rear wheels you can't hear yourself fart at 70 MPH.

I would like to keep the Benz quite as possible thinking maybe a manual switch to a relay and watching the temp gauge.

Johnboy

__________________
79 300D
94 F-350 PSD
00 Excursion PSD
71 Karman Ghia (only gasser in the bunch)
2002 Club Car Golf Cart 48V 8" lift