Have a 82 240D which the starter motor will not engage unless the purple wire is jumpered to the battery connector on the starter. It starts by using the key sometimes and others it doesn't. When the starter motor fails I've observed and measured 9.5 VDC across the purple ignition wire. When it does work, the same purple wire connection on the solenoid has 10.5 volts. It appears there is a voltage drop.
Jumping this solenoid connection with the starter/battery connector works every time, but using the key to start the car does not.
Yes it could be the ignition switch, the headlight switch, or the neutral safety switch which is causing the voltage drop. Other posts which I've read state that there should be close to 12 VDC at the purple wire solenoid connection or close to battery voltage. Is my thinking correct or am I missing something. Any help would be appreciated.

Thanks
Greg

I'm not sure why you think it could be the headlight switch.

It certainly could be the ignition or the neutral safety switch. It could also be a loose contact someplace or a weak ground connection. Have you tried shifting to neutral instead of park when it fails to start?

Try seeing what the Voltage Drop is with the Glow Plug Relay unplugged (disconnect the Connector that would hook the Relay to the Ignition switch; I believe it is sort of a six sided connector on the Relay).
When you are actually cranking the Engine your Glow Plugs are also to be on.
The solid Violet colored Wire goes to the Glow Plug Relay.

The Violet Wire with a White Strip comes from the Ignition Switch down to the Starter Solenoid and is where the solid Violet colored Wire gets Voltage from when the Key is turned in the start position and turns the Glow Plug Relay on during Cranking.

Your Battery Voltage dropping as low as it is could also be a tired Battery. If this was a Gas Engine and your Battery Voltage dropped to 10.5 Volts even if the Starter was Cranking OK your Engine would not start due to not enough Voltage for the Coil to work OK.

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84 300D, 82 Volvo 244Gl Diesel

There's a thread on here describing how the clean the contacts in the ignition switch to solve such a problem. There are also pictures of people installing a Ford starter solenoid switch near the battery to solve the problem.

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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

Thanks guys for the help. A little history might be in order. Upon purchasing this car, the former owner told me that every once in a while you would need to short/jumper with a screwdriver between the battery connection on the starter motor and the purple lead from the ignition switch. I first suspected that the starter needed to be rebuilt. So, I had a local generator shop rebuild it. The owner said that it had been underwater at one time and the brushes were shot. Obviously he replaced them and checked out the entire circuit plus the solenoid. I trust this shop for I've had him rebuild a number of starters and 40 yr old old tractor generators for me in the past, plus he's been in business for about 50 years.

Craig, the reason it could be the headlight switch is in the following attached schmatic. This is from the MB CD for the car. I was breaking down the componets of the ignition system to issolate the voltage drop. Since the Ignition switch, according to the schematic gets its power from the Light switch, that would be a good starting point.

I thought of the NSS also. I Did move the shifter from park to neutral last night with the ignition switch turned to the start position to test the NSS. Didn't start.

Diesell911, I'd try the glow-plug relay, but the former owner disable the relay in favor of a toggle swithc mounted on the kick panel. So the glow-plug system currently functions independantly of the ignition circuit.

The battery voltage is 12.85 VDC.

I called the generator shop this morning which had rebuilt this starter inquiring about the voltage at the solenoid. He told me that there are many VW's and Mercedes which they have had to put a, "5 wire relay", in because of the low voltage at the starter which he said developes over time. I'll find more about this for and let you know.

Kerry: I agree about the switch. It's 28 years old and could be the problem. Doesn't take much resistance two cause a 3 volt drop. Don't have a problem with cleaning or replacing it.

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Well, I wouldn't say that diagram says the ignition get's it's power FROM the light switch, but it says power connects there first... if your lights come on, that's not the issue.

apparently the light is the first stop on the path to the ignition switch. but a totally blown out light switch would have no affect on the ignition, unless there was a fire or something... it's just a junction point.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
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My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

VSTech: I agree!

Every connection is a suspect. Since it makes a connection at the light switch first before going to the starter solenoid, it wouldn't hurt to check /clean/ tighten that connection, as well as other connections such as battery terminals etc.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I dont know the condition of your car over all. But if you dont mind a little jerry rigging - why not run the jumper wires into the interior and put a switch in place there. so when the ignition fails to start the car - push the new button or flip the switch on your jumper and off you go.

At least then your not under the hood in the parking lot at work with all your buddies laughing at you.

BrassMonkey: I had thought about doing that as a backup to the regular ignition also, and plan to implement that as a alternate solution.
A thought occurred to me after looking at the schematic again and remembering something I saw when installing the starter motor after having it rebuilt. On the starter motor there are two connectors. One large and the other small. The large connector contains two wires. The first being the battery cable and the other being about 5 wires which are crimped all into one connector. The schematic shows a wire going from the battery to a post on the light switch and another wire going from the same connector to the ignition switch. I have wiggled these (the 5 wires crimp connector) wires before and the ignition started working. This was shortly after I purchased the vehicle and re-crimped all these wires into a new lug. Since it appears that the ignition power going thru the ignition switch then thru the Neutral Safety switch originates at the battery terminal of the starter, there could be resistance built back up within those 5 crimped wires causing what appears to be a starter problem.

I have the same starting issue with my 1985 300D. I've done a lot of work on this. New shifter bushings, tested NSS, just to mention a few. I did not know about the headlight switch possibly being the culprit, but I wiil check it. I still have the intermittant problem.

BrassMonkey, I tried running two wires to a switch in the cabin, but obviously, I needed some real heavy gauge wire. It draws way too many amps. I think I used 12-14 gauge wire. It wouldn't do anything.

I wrote to a guy on here who had a post about installing the Ford starter solenoid, and I think that's what I'm going to do. He said to use one from a 1965 mustang or something. I certainly don't want to spend the money on a new starter and end up with the same issue. Not to mention what a pain these starters are to swap out.

You can read my original post here: http://www.peachparts.com/shopforum/diesel-discussion/316631-1985-300d-starting-issue.html

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'85 300D 190K miles
running on B100 Biodiesel since 156K, SCRATCH THAT! I can only find Biodiesel at 1 location in Houston! (not very convenient)

Below is a pic of a Ford Type Solenoid. In the case of the Picture I am using it for a Glow Plug Relay.
I paid about $5 back in 1992 at at Junk Yard for it.

Also the Stock Starter Solenoid does not draw much Amperage if it is working normally. If you look at Remote Starter Seitches they do not have heavy Gauge Wires on them.

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84 300D, 82 Volvo 244Gl Diesel

The starter solenoid draw 8A max. Ford starter relay is way overkill. Connect a DVM (digital volt meter) to the starter solenoid terminal (the small one). You should see around 11 to 12 v while the key is in start position. If less you have a problem

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked