My sons 81 SD recently failed to start for him one night after work. So I took my tool box and jumper cables to see if I could get it home. In this particular case the engine was not turning over at all, only the glow plug relay was cliicking. So I did not know if it was the starter solenoid or the key switch which go bad in these things.

Here are some steps to diagnose starter problems and get you home:

Find the black plastic wire junction box normally located on the right fender.

The small purple wire is coming from the ignition switch.

The other wire connected to the purple wire is going on to the starter solenoid.(with a meter you should be getting 12VDC here during start)

If you are getting 12VDC during start here, your starter switch is good and chances are your starter or solenoid on the starter is bad. Just CLICKING sound is probably sticking solenoid. GROWLING noise is probably starter or low BATT charge.

If you are not getting 12VDC at this juction you have an ignition switch problem.

An easy way to bypass the switch is to diconnect the purple wire with the wire going to the solenoid, turn the key to the start position, jumper the wire that is connected to the purple wire to the POS post of the battery and the car will start and get you home where you can replace the switch housing or tumbler or both.(very easy jobs)

Tools required - phillips screwdriver and jumper cables

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I LOVE CATS....AND FRIES

1981 300sd
1983 300sd
1985 300d
1983 300cd
1991 350sdl

Jumping terminals 1 and 3 in that junction box should get it going without having to disconnect any wires if the battery and starter are good.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

If the starter is bad, just tow start it. It doesnt take that much to get the manual ones going. About 40mph will get an auto going.

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Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

Is this junction upstream or downstream of the neutral start switch? The NSS is a more typical failure point than the key switch (it doesn't initiate ignition ).

Sixto
87 300D

I would love to hear equivalent jumping instructions for an 80 300td. The cable bundles seem to run straight back behind the firewall, so I'm guessing it's a more complicated procedure. Thanks!

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1980 300TD

Oh yeah, also: I can't tow or roll start, because for some reason this transmission won't downshift manually, except during acceleration.

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1980 300TD

Can I consider bypassing the neutral safety switch (perhaps permanently?)

Thanks for all input!

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1980 300TD