Glow plug light

[JimmyL]

I searched the archives for why the glow plug light would stay on, or flick back on after starting the car, and the posts pointed to the glow plug relay. Could someone tell me where this is located in the car?
Thanks,
Jimmy

[lucforce]

black box, inner fender, wires go in it

Drivers side, about even with the engine front.

[JimmyL]

Can this relay be repaired, ie:contacts burnished, or would a new one be the plan?
JL

[leathermang]

This is one of those times when something going wrong is a GREAT excuse to Eliminate it..
I say wire the glow plugs to a normally off switch you control with your finger.... why they thought people were so lazy they could not keep their finger on a good old fashioned switch I don't know... but it is just one more thing not actually needed which can go wrong....

[P.E.Haiges]

JimmyL,

If the GP work OK, why bother spending the money to fix the GP light? My GP light works intermittently. When it doesn't light, I just guess about how long to wait fot the GP to heat.

You might also have a bad GP. Do a resistance check on your GP. Its quick and easy and will find a bad GP if you have one.

P E H

[autozen]

Jimmy,

It has been my experience over the last 30 years that these relays have a low failure rate. Before I replaced it or wired around it I would follow the MB test procedure. The light may be tellinmg you that you have 1 or 2 glow plugs out which is one of the functions of the relay. If you do wire in a switch, make sure it is a MOM switch that opens when you release it. Another function of the relay is to time out after about 110 seconds so you don't totally drain your battery if you leave the key on.

Peter

[JimmyL]

Let me ask another question based on the archived info. It was stated in a couple of post that if the light was on, the glow plugs could still be on. It even mentioned the end burning off and falling into the engine. I'm not worried about the light being on really, just worried about what the light being on could mean. Also, wouldn't the glow plugs have to be removed to check resistance, as I'm assuming you need to have the meter on each end, like checking windings or somesuch.
JL

[P.E.Haiges]

JimmyL,

You don't have to remove the GP, just the GP cable connector from the GP relay so you don't get parallel resistance measurements. That's what makes this test so easy and quick.
Do a search an Ohmeter and you should find the procedure.

THe GP light does not necessarily tell you the GP are on. Do this: Turn on cabin light. Turn key to run position, you should hear the GP relay click and notice if the light dims. If it dims, GP are heating. After about 45 seconds, the GP relay should click off and the cabin light should get brighter. If it does, it means the GP relay is working correctly and turned the GP off.

P E H

[JimmyL]

Thanks P E H
I will check that tomorrow, and search for the procedure tonight!
Jimmy

[JimmyL]

OK, I checked to see if the dome light dimmed upon turning on the glow plugs, and brightened 45 or so seconds later. Did both just as it should, demonstrating a working relay I assume. So, I accessed the GP relay assy, and 2 questions remain. The first, and I know I should know this, but to check for ohmage of the glow plugs, one probe goes to one of each of the 5 wires on the larger disconnected connector. Where does my other meter probe go? If I'm reading through the wiring and the glowplug, what completes my 'circuit'? When I start my '80 300TD, it shakes and sputters quite violently for several seconds if not more. Then it runs fine.

My next question, and I've included a pic, is what on earth is this red wire doing? It is the same type of wire that the PO had the AC system bypassed with. Looking in my Haynes manual schematic, which I don't read schematics that great, seems to have something to do with the AC system. Is something else bypassed here?
There is a guy here in the Dallas area who always has 123's for sale in newspaper. Last 4 digits of his phone # are 3944. Stay away, I promise! I can't tell you how shady his work is, and what all he does to quickly sell these cars. My problem, I didn't educate myself until after the fact. My fault. But thanks so much for the help to straighten some of this mess out.
Jimmy L

Hi Jimmy.

That what you have is a potential for a
disaster.

This is what should be there.

[lucforce]

an 80 amp fuse link should be there

[P.E.Haiges]

JimmyL,

The other lead of the ohmeter goes to any good ground. One way to check this ground connection is to measure with the other lead also connected to ground. When you get the minimum reading on the ohmeter by wiggling the leads to get the best connection, don't disturb the ground connection and start reading the resistance (ohmage is not a word) of the GP.

Where the red wire is, there should be an 80 amp fuse.

P E H

[redbaronph123]

i'm sorry to sort of hi-jack the thread of another... but i also have a GP query...

at times my GP light doesnt come on.. and i know that the plugs dont heat up because the car just wont start in the morning after i count to more than 15 seconds (ideally i only count to 10, wherein my GP light goes off at 7seconds).. but it just wouldnt start. What's wierd is.. the GP light returns to normal working order after the engine gets cranked once.. then the glowplug light turns on and the GP heats up.. then i can start the car... where should i start to check?.. should i simply check the GP relay?

i'm thinking of checking if there is a load on the fuse bar.. when i first turn the key on (where the GP should be heating up).. and see if the problem is simply a bad connection.... but hopefully i culd get some guesses from you guys.. or better yet... expert opinion on where i should exactly look and place my multimeter rods to check.. .hehehe

TIA