Fast glow upgrade conundrum - PeachParts Mercedes-Benz Forum

KAdams4458 · #1 11-17-2010, 08:30 AM

Update: See post # 19 for specific upgrade wiring info.

I started pondering this when I recently started to put together an updated parts shopping list for the engine swap. Bear with me on this one. It's been decided that the car will definitely get a fast glow upgrade, but this isn't a simple upgrade.

The car: '77 300D, OM617 (Loop style plug setup)

The replacement motor: '83 OM617 (Pencil plugs setup)

The way I see it, I apparently need to buy the fast glow kit for the loop plug cars that includes four fat pencil plugs that I don't need, and then I have to buy five new pencil plugs that fit the '83 motor. Fun. I'd really rather not buy a kit that includes the fat loop to pencil plugs and jumper wires if I don't have to. Sadly, that might be the only way to get this done.

I do have the the entire '83 donor car, just in case anyone wants to tell me that wiring up the later pre-glow system in the '77 is something that isn't too involved. Maybe someone has done it? I figured that this was a question worth asking before I buy parts that I have no use for just to get the parts that I do need.

funola · #2 11-17-2010, 08:46 AM

Am I missing something? Seems like the thing to do is take the glow plug harness and controller from the 83 and install into the 77?

kerry · #3 11-17-2010, 09:21 AM

I must be missing something. All I would do is use the pencil plugs in the new engine, make jumper wires to go between them and hook the one nearest the firewall up to the wire that energized the former loop plugs. I don't see why you need to replace the relay.
Now wait a minute, maybe the issue is that the old relay has a temp sensor wire going to the engine on the old system and no temp sensor system on the new engine? If so, I think you should be able to swap over the old temp sensor, or operate the old relay without a temp sensor?????

vstech · #4 11-17-2010, 09:55 AM

yuup. you can leave the plugs in the car, hook wires to them all, and run it to the connection on the firewall and as long as your existing relay is working, you will have fast glow function. no money to spend at all. well, you should upgrade the 50 amp fuse to an 80 amp fuse.
if you want to get really fancy, you could pull the wiring harness, and relay from the donor car, and wire the newer relay into the circuit. but I don't know exactly what you'd need to do to tie it into the circuit.

kerry · #5 11-17-2010, 10:26 AM

Anyone know the scoop on the temp sensor? Later relays had the temp sensor in the relay and not in the engine. Will the older relay work without a temp sensor hooked up to it?

Diesel911 · #6 11-17-2010, 11:01 AM

Quote:

Originally Posted by kerry

Anyone know the scoop on the temp sensor? Later relays had the temp sensor in the relay and not in the engine. Will the older relay work without a temp sensor hooked up to it?

From what one of the members said the Temp Sensor (on the Loop/Filiment type Glow Plugs) just controls the Glow Plug Light while at the same time serving as a ground for the Glow Plugs.

In this thread:
1976 Glow Plug Update but no voltage to the glow Plugs when key is turned on
http://www.peachparts.com/shopforum/showthread.php?t=181503&highlight=pencil+plug+relay+ground+wire+115
and a more recent one the stock Relay would not work with the New Style Adapter Glow Plugs.
I am not sure but if you look at the diagram of the Relay there is a Reed Switch inside of the Relay. I suspect that the Reed Switch is OK with 50 amps but not 80.
But, I actually do not know.

Also if he used a Relay from the 83 would he be able to wire the adapter Glow Plugs in parallel instead of series?
If so I think that would be an advantage.

KAdams4458 · #7 11-17-2010, 11:05 AM

Quote:

Originally Posted by funola

Am I missing something? Seems like the thing to do is take the glow plug harness and controller from the 83 and install into the 77?

You're not missing anything. That's really the main question in my head, and the reason I created this thread. It sounds great to me, but I have no idea how deeply that wiring in rooted in the car. I was hoping that someone here has already done exactly the same thing, and would stop by and give me some encouragement and/or tips.

KAdams4458 · #8 11-17-2010, 11:15 AM

Folks, the timer in the '77 is one of the early ones, it's NLA, and it fried to death some time ago. I did manage to reconstruct it with salvaged electronic components from an old pinball machine, so it does currently function. Unfortunately, the relays inside of it are on borrowed time, and it's just not worth putting any more time or effort in to. The old pre-glow system has to go in order for this car to be a reliable daily driver.

Quote:

Originally Posted by vstech

if you want to get really fancy, you could pull the wiring harness, and relay from the donor car, and wire the newer relay into the circuit. but I don't know exactly what you'd need to do to tie it into the circuit.

Dang it. I was kinda hoping you might have some ideas. I need some wiring diagrams that I can actually read.

kerry · #9 11-17-2010, 11:17 AM

Quote:

Originally Posted by Diesel911

From what one of the members said the Temp Sensor (on the Loop/Filiment type Glow Plugs) just controls the Glow Plug Light while at the same time serving as a ground for the Glow Plugs.

In this thread:
1976 Glow Plug Update but no voltage to the glow Plugs when key is turned on
http://www.peachparts.com/shopforum/showthread.php?t=181503&highlight=pencil+plug+relay+ground+wire+115
and a more recent one the stock Relay would not work with the New Style Adapter Glow Plugs.
I am not sure but if you look at the diagram of the Relay there is a Reed Switch inside of the Relay. I suspect that the Reed Switch is OK with 50 amps but not 80.
But, I actually do not know.

Also if he used a Relay from the 83 would he be able to wire the adapter Glow Plugs in parallel instead of series?
If so I think that would be an advantage.

The 76 115 has a different relay than the 77 123. The 77 is not grounded thru the temp sensor. That system grounds directly to the block. I agree that the temp sensor only controls the length of time the light is on and nothing else. So would the light work at all without a temp sensor. Is there a threaded hole in the block for the second temp sensor on an 83 engine?

The wiring is quite different for the relay between the 77 and 83. The relay for the 77 is up under the drivers footwell kick panel. The relay for hte 83 is on the left inner fender. I would use the 77 relay and if I couldn't get the light to work because of the temp sensor issue, I'd just go without a light.

KAdams4458 · #10 11-17-2010, 11:19 AM

Quote:

Originally Posted by kerry

Anyone know the scoop on the temp sensor? Later relays had the temp sensor in the relay and not in the engine. Will the older relay work without a temp sensor hooked up to it?

I don't know if they are all the same, but the very early versions like mine will default to a full 30 second glow cycle in the middle of summer if you unplug the temp sender.

vstech · #11 11-17-2010, 11:19 AM

I think it's just got a power wire from the ignition switch and a sense wire from the starter on it. along with the battery wire of course. you should be able to pull the harness from the donor car and have no issue with it.

kerry · #12 11-17-2010, 11:21 AM

OK, given the new info about the failed existing relay, there's no doubt what I would do. I'd wire in a Ford starter relay to a button somewhere in the car and control the glow cycle manually, kind of like the old gorilla knob system. I'd use the existing strip fuse block on the firewall as the fuse in the system. I think direct driver control of the glow cycle is superior to a timed relay. No brainer.

vstech · #13 11-17-2010, 11:25 AM

Quote:

Originally Posted by Diesel911

Also if he used a Relay from the 83 would he be able to wire the adapter Glow Plugs in parallel instead of series?
If so I think that would be an advantage.

all the pencil plugs are wired in parallel. the retrofit appears series, but its parallel too.

KAdams4458 · #14 11-17-2010, 11:29 AM

Quote:

Originally Posted by kerry

OK, given the new info about the failed existing relay, there's no doubt what I would do. I'd wire in a Ford starter relay to a button somewhere in the car and control the glow cycle manually, kind of like the old gorilla knob system. I'd use the existing strip fuse block on the firewall as the fuse in the system. I think direct driver control of the glow cycle is superior to a timed relay. No brainer.

I'll see your no brainer and raise you "the wife factor."

She won't like that, no matter how effective it is.

Quote:

Originally Posted by vstech

I think it's just got a power wire from the ignition switch and a sense wire from the starter on it. along with the battery wire of course. you should be able to pull the harness from the donor car and have no issue with it.

Hmm... Could it really be that simple? I could have sworn their was more wiring to it than that, but there are probably a few grounds in there too, eh? Perhaps I will find an excuse to pop the hood and look at it today.

kerry · #15 11-17-2010, 11:40 AM

Are you saying that MB got rid of the gorilla knob system in order to attract female diesel drivers? Give your wife a shot of testosterone and install a spring loaded rocker switch.