glow plug a draw on charging system?

[calcars2]

I have a 84 300 D
my glow plug light comes on while driving ( or stays on once car is started/ driving) for unexplained reasons. If that light goes off, and I drive for a while, everything is OK
Especially at night with that light on it will run down my electric system- thus causing the car to not have enough power for a restart
Battery and alternator have tested OK
Question- would bad glow plugs ( or relay) cause a draw down on the charging system ?
Thanks

[spdrun]

Bad relay, most likely. Glow plugs also aren't rated for long-term operation while the motor is running, so they may melt to the prechambers. Get it fixed yesterday.

[vstech]

you may have an "afterglow" relay installed. they are known to bring on the plugs for as much as 3 minutes after starting the car for cold running... if it was installed wrong, it's possible it's coming on for longer... the stock 55/65A alternator is not capable of supporting the headlights, the a/c blower, and the glow plugs.
I agree, get it fixed yesterday!

[tangofox007]

Originally Posted by calcars2

Question- would bad glow plugs ( or relay) cause a draw down on the charging system ?

When it comes to "drawing down" the electrical system, it's the good glow plugs you have to worry about, not the bad ones. Either way, the plugs are not the cause of the problem. Either the preglow timer has suffered a failure or there is an intermittent connection between the timer and the start switch that is causing the timer to cycle back on repeatedly. Since the light is coming on, the problem is not with the relay itself.

For a temporary solution, you could disconnect the glow plug harness after you start the engine.

[compu_85]

Originally Posted by vstech

the stock 55/65A alternator is not capable of supporting the headlights, the a/c blower, and the glow plugs.

The stock alternator can hardly run the headlights and blower on low

-J

[calcars2]

Hi Tango
where is the timer located ?
Thanks

[tangofox007]

Originally Posted by calcars2

Hi Tango
where is the timer located ?
Thanks

Inside left fender, behind the left headlight. Black, plastic box larger than a pack of cigarettes. Lid on top pulls off.

[calcars2]

tango
I actually replaced that silver metal bar ( fuse??) burned, years ago- way before problems started.
the circuit board in that black box looks very clean, and functional
from the picture on auto zones web site ( of a relay) looks similar to the top of the black box with the metal bar on it?
there is another plastic blk. box on top of the inner fender, with two square fuse links in it- whats that for?
and where is the easy plug in ( haha... nothing is easy on this car) glow plug harness?
thanks again
but I can change my oil...

[tangofox007]

Originally Posted by calcars2

tango

there is another plastic blk. box on top of the inner fender, with two square fuse links in it- whats that for?

Aux fan and a/c compressor relays.

Originally Posted by calcars2

and where is the easy plug in ( haha... nothing is easy on this car) glow plug harness?

That would be the forward connector on the timer box.

[calcars2]

the forward connector ( 5 plugs) .....
how about if we talk ??
PM me for Phone Number!
or yours?

[calcars2]

think I got it figured out
once warn I unplug both plugs
thanks

[retmil46]

If you can still find them in the parts stores, those small digital voltmeters that plug into the cigarette lighter are well worth the $12 they cost.

had something similar happen to my first 87 300D - PO had done the "purple wire mod" aka "poor man's afterglow" on the GP harness - by snipping that purple wire, it caused the GP timer to kick in for another complete cycle after the engine was running.

And of course, the timer decides to stick on on a 102 F south Texas day, with the A/C on full blast.

Fortunately, after only 15 miles or so, rolling along at 70 mph, I look down at the digital voltmeter and it's only showing a little over 12 V. I shut off everything electrical and rolled down the windows - still only just over 12 V. WTH?? A couple miles down the road I pull off into a rest area, and on a pure hunch, pop the hood and pull the GP connector on the relay. Bingo, voltmeter soars back up to 13.5 volts.

I left it unplugged the rest of the day. 102F outside, a hot engine with only 145K miles on it and good compression, it would fire right over on the first crank.

Next day, gsxr came to my rescue on one of the other diesel forums and told me to check the purple wire.

When I got the second 87, one of the first things I checked when it rolled off the carrier was to pop the hood and check the GP harness to see if anyone had monkeyed with that purple wire.

If I ever get around to putting a set of permanent gauges in this 87, one of them is going to be a frakkin voltmeter!!!

[bd1308]

Hey not to be a bother here, but you may want to remove your phone number from this thread if you dont intend to have it publicly available.