Pics: Inside a glow plug relay
 

Hello everyone,

I dont think I ever recall seeing any pics of what was inside a glow plug relay box so as I've decided to snap a few pics for anyone who's interested in taking a look:

This box is part number: 001 545 98 32
It is for a 5-cyl 617

http://img.photobucket.com/albums/v6...9/IMG_9447.jpg
http://img.photobucket.com/albums/v6...9/IMG_9448.jpg
http://img.photobucket.com/albums/v6...9/IMG_9449.jpg
http://img.photobucket.com/albums/v6...9/IMG_9450.jpg

This one came out of my green SD as part of a diagnostic and was replaced with a known working one from my gold SD.

After fixing the issue with the green SD, I've tried to reinstall this one into my gold SD.

It appears to be dead. No cluster light. No voltage at glow plugs.

Correction: It works, just needed some cleaning on the terminals.

Thanks.

I took one apart a couple months ago that was malfunctioning (staying on)....nothing looked wrong physically, but I did not waste much time on it as I had a good used one on the shelf.

What I love most about my car is the fact that the radio is probably the most advanced electronic gadget in the car.

I love how you can follow solder paths on the board. Try doing that with a modern computer!

An emery board cut down the center to make it much thinner is a great tool to clean those contacts with too. The thinner the better as long as the contacts dont tear it.

When your thru sanding the contacts a quick wipe with rubbing alcohol is a good thing to do to insure everything is smooth and clean.

Back when I used to run a Video Game arcade, we'd use a dollar bill to clean contacts for joysticks and buttons. Very low abrasion and high utility as far as cleaning electrical contacts. Might be useful for the final buff. :P

Also useful for cleaning valves on musical instruments, rolling papers are good too.

with the advancements in electronics today, the new relays should have
smaller components and/or less of them to do the same job.

the printed circuit board, looks like some we used when I worked for
Sylvania back in 68.

Charlie

The biggest advancement nowadays would be to get rid of those in-line current sensing coils, and have Hall-effect type current sensors just mounted next to the high-amp lines. And, there would be one per glow plug, none of this "first one" or "last one" or "something in between" guessing game.

The guessing game is a result, in part, of the same component being used in both four and five cylinder engines.

I've managed to grab spare glow-relays for my '82 240D and '84 300TD at my Pick-N-Pull. At least on my cars, they aren't identical. Haven't tested either spare but they were cheap enough. I suppose I could rig a push-button switch to do the job - so long as I didn't heat the plugs long enough to fry them. Anyone know the price of a new glow-relay?

Happy Motoring, Mark

0015459832 (300TD)
0015459732 (240D)

They're about $100 for each of them...

Sounds reasonable, compared to some prices I've recently heard for W123 parts - like $800 for a heater-blower, or $1200 for an SLS-pump!

Happy Motoring, Mark

For that price, looks like its time to build my own.. As long as the contacts are still good, replacing the electronics is a breeze...

After two earlier unsuccessfull attempts, this evening I finally found a Hella pre-glow time-relay listed under 'body-electrical' on Fastlane - for $193.50.
It supercedes the earlier designs and replaces both W123 240 and 300 diesel glowplug relays.
This upgrade part operates the glowplugs for up to 3 minutes after engine startup and appears to require replacement glowplugs.

Happy Motoring, Mark

I've had one of those in my 300D for about 5 years now, it works well. Just one word of caution, if you take lots of very short trips you may find the battery running down because the alternator has trouble keeping up with the post-glow demand while charging the battery. It's not an issue if you drive more than a few minutes after starting the car.

How did you arrive at that conclusion?

By reading the information posted by Fastlane for their Hella pre-glow time-relay.

Happy Motoring, Mark

Could you post a link? I can't seem to find any reference that states that the Hella relay operates in the "afterglow" mode or that it requires different glow plugs.

This is definitely not true for all W123 year models.

Thanks. But that is a Bosch part, not Hella.

I thought only Bosch had an afterglow relay for the W123.

My search was for my '84 300TD. On one Fastlane page, below the Bosch relay, was listed an optional Hella Preglow time-relay, Part# 1331607146, for $193.50
I'll let someone else figure out what's the difference.

Happy Motoring, Mark

Is Hella better than Bosch?

I've got Bosch units in both my SD's, they are probably original. Seem to be working flawlessly (the one needed the terminals cleaned)

I've no complaints.

That approach seems to be a bit inconsistent with your "Happy Motoring" philosophy. Anyone buying a Hella relay and thinking they are getting an afterglow unit isn't going to be happy. Neither is their wallet.

There was no explanation on the page for the difference. Maybe the Bosch is made in Singapore, while the Hella is still made in Germany.
Maybe someone could call Phil for an explanation.
Meanwhile, as I mentioned, I already got spare glowplug relays at the Pick-N-Pull

Happy Motoring, Mark

Pre-Glow? Post-Glow?
 

Guys, help me understand this. I live in the tropics (practically speaking) and detailed operation of the glow plug relay has always been low on my list.

The standard pre-glow relay operates the glow plugs for a variable, temperature dependent time period. There was a later change in the relay that keeps the plugs lit for a period of time after startup? Also dependent on temperatures? Do I have this right?

The Fastlane page said for up to three minutes after startup, to reduce smoking during warmup. It appears to require replacing the original glowplugs with a different type. Probably not an issue in a warm climate, but now I wonder if the standard glowplug relay is NLA.

Happy Motoring, Mark

Sorry to bump an old thread, but I thought I'd post some photos of my fried Glow Plug Relay. Any ideas what would have caused this?

http://i.imgur.com/58fLQ.jpg

http://imgur.com/TX0dM.jpg

http://imgur.com/qvveQ.jpg

I've replaced all five plugs and will check the wiring harness to make sure my ground is good. Is there anything else I should check before dropping in a replacement relay?

Man, there was some serious heat going on in there. strange the fuse wouldn`t have blown to protect it.

Possibly a component inside the relay failed, but not drawing enough current to blow the strip fuse.

You can pick up a used one from PNP for around $10 to see if it was the relay or something else causing the problem, before buying a new one. but I`ll put my money on something in the old relay causing the heat.

Charlie

that's what the relay will look like if it sticks on. the ampdraw is low enough to prevent fuse failure, but constant enough to build heat inside the relay and melt plastic, etc...

Looks like poor contact of the fuse strip which results in local heating at the contact area which melted the plastic. If you have continuity in the coil and no shorts, cleaning the fuse contact and making sure the 2 fuse screws are tight it may work just fine

Rolling papers are useful for so many things!

I'd agree. Just a little resistance could cause quite a lot of heat with the amount of current being drawn. Make sure the relay contacts are clean too. Use rolling papers to their best effect, then clean the relay contacts.

I cannot get my preheating to work, no light at the dash, no heat either.

I remember that just before the preheating light stops working, a strange sound like of short circuit was heard sometimes from the inside the dash at the left close to the door.
It is possible the some other fuse or relay could be damaged than the glow plug relay instead and it is the one to blame instead of the glow plugs relay??

I any case, does anybody here know how to test a glow plug relay and cables to it with a multimeter?

That is ...

1) voltages in the female pins in cable coming from ignition when it is set on and when is set off?
2) voltages in the corresponding male pins in the relay when the cable is removed but the relay is connect to battery?
3) voltages at the relay male pins out for the glow plugs when the ignition is set on and when is set off?

BTW, when I test the continuity of current in the female pins cable from the glow plugs (negative attached to the negative battery) I get a lecture in my multimeter in all the pins between 1.5 and 1.8 (set at 200 ohms position on tester).
I read here
http://www.dieselgiant.com/glowplugrepair.htm
that these values must be below 1.
So from it, I conclude my glow plugs are bad but working yet, so these cannot be the issue with my problem.
That was why it always start with some difficulty at mornings, but not like now.

Ideas???


TNX

When my glow plug relay went out a few months ago, the dealer wanted $270 for one! I ended up buying a used working unit from the PickNPull for $12.

If that didn't work, I'd probably get a new one either from Pelican or possibly Walt (He carries the newer Hella type ones that glow a lot longer).

Packman

Does the dash pre-glow light come on with the "light check" function when you first turn the key? This is when all the lights in the instrument panel are supposed to light up as a bulb check. If not, then your bulb is dead.

If there are 12 volts at both ends of the strip fuse at the pre-glow relay, then your relay is _probably_ getting power.

Remove the fuse. Hold it in your hands, flex it a little. If it crumble or breaks, or if a crack becomes evident, the fuse must be replaced. It is an 80 amp strip fuse, not easy to find locally except maybe an MB dealership. Check with FLAPS, some do carry them, they certainly can order them.

If your multimeter is not a good, accurate meter, it will have a hard time measuring a resistance of less than 1 ohm. I wouldn't be to worried about those values if you have a cheapo-meter that cost less than $50 or was made in china. The resistance test is best used to find dead shorts (zero ohms) or blown plugs (infinite resistance). Very unusual for all the glow plugs to fail at once, so if the readings are consistent, they are probably good.

Beyond that, you'll need a wiring diagram to chase down all the wires and what each should measure.

Really, the "best" way to see if your glow relay is working is watching for the slight dim of warning lights when the relay engages upon turning the key. If the car sits a while between starts, the FSM recommends cycling the key several times to the #3 position to charge an internal capacitor of the glow relay.

As mentioned, it is difficult to really determine the quality of a glow plug with an multimeter. The best way is to remove the glow plug and attach it to the harness, while suspended in free air. (CAUTION! Absolutely do not touch, even accidentally, the plug while there is even a possibility of it being hot. Major burns are possible!)

Most likely, from your description, you have a glow plug or two that are on the decline. Some folks onesy and twosy the replacement of the glow plugs but I'm of the mindset to change them all at once and be done with it. I figure that if one or two fails then the others will not be far behind. Murphy's law states that they will fail at the worst time and situation.