Glow Plug Wait Lamp problem coming on randomly

[TGP (IL)]

Glow Plug Wait Lamp comes on at random while driving.

I have searched and read numerous threads on this, but come up
Empty, because of dead links, or never updated the fix, or not exactly my problem.

M1028A2 Glow plug system operates as intended and starts fine.
After starting the light goes out and after glow stops, then high idle kicks off and were good to go.

Then while driving the GP light will come on, or flicker, or dim, or go back out only to come back on.
When this happens the GP controller don't energize the plugs, which is a plus, just the light.

I have changed GP Temp. sensor, swapped GP card with new one, checked wires, grounds, all seem good.

But, now I believe my problem to be a ground issue because I find all is well until I turn on the service light
Switch to activate service lights.

GP Light stays out until, you turn on headlamps, or, heater, or just brake lamps, wipers, etc.
Basically loading the electrical system, the light will turn on.

So I rechecked controller ground, dash ground at the buss bar by the E brake, and all the other
Grounds under the hood.

So I'm lost.

Naturally if I remove the GP card the light stay's out.
All service lamps are bright and no sign of weak currant.

Gen 1 has 14.Volt at battery, Gen 2 has 14.2 at rear battery, 28.2 across both.

Could this be a + side power issue somewhere?

From what I see in the schematics power is applied via ign. switch to the wait to start lamp and
Controller supplies the - ground when needed to complete the circuit.

Any Ideas?

Thanks for taking the time to read this.
Tom

 

[MarcusOReallyus]

I agree it sounds like a ground problem. I'd be doing some testing with a good multi-meter to verify ground integrity from the card connector to the battery negative terminal. Can't hurt to verify supply voltage to the card connector.

It's also possible that there is a fault in the card itself, but I'd really scrub the ground to the card first, then the supply voltage.

 

[Tinstar]

Check the wiring coming from the GP card housing very close.
Others have had old wiring break, but the insulation showed no external damage.
Agree also about the grounds.

Just a thought.

 

[TGP (IL)]

Thanks for the help.

I will recheck the grounds again.

Have multiple digital VOM and my trusty Simpson 260.


Appreciate the help and direction.
Tom

 

[TGP (IL)]

Well not much progress.
Using VOM at the GP Controller plug, I have 12.29 volts between Ing. 12v power pink/blk 39A
And controller ground Blk 151A.

I have sprayed and cleaned the connection to the GP Card, pulled apart and cleaned the
four wire connector upstream from the card.
Cleaned and checked all connections at fuse box.
Everything looked good.

I think my next step will be a long jumper from controller ground #151A to Neg Buss Bar
And see if any difference.
Tom

 

[MarcusOReallyus]

That is an excellent idea.

 

[TGP (IL)]

Ok, I got out my retractable leads and connected the control ground to Neg. terminal on battery no change.
While had it out I backed up other grounds under the dash no change.

Now starting to think in another direction.
I have noticed lower volt reading from the dash gauge.
It climbs up to upper green, but slower than usual.
When I turn on the lights, or other loads, it falls more than usual, stay's in the green but low.

So with engine running, I have 14.3 Volts at the Alternator#1 output stud, and at the Firewall 12volt junction block(diamond).
But only 12.8 to 13.5 depending on how long I let it draw, inside the truck at the controller Ign. feed, Or the power sides of the fuse block.

Follow the wires as per the drawings through the bulkhead connector and from there to the Ign. switch.
I removed and cleaned the bulkhead connector, looked good btw, no change.
Removed and cleaned each fuse and looked at the back of the fuse box,no obvious problem

By now my back is killing me so it was time to quit.

Going to drop the steering column and check voltage's at the Ign. switch.

I think there is a voltage loss someplace, and if that could be triggering the wait to start lamp?

I understand the power feeds back to the fuse box from the Ign. switch, so need to look at that.

To be continued.
Tom

 

[TGP (IL)]

Found the problem.
Ground issue from Neg. post front battery to the engine.

Either front Battery Neg. to Buss Bar, or Buss Bar to rear Engine, haven't checked
Any further, but will.
All seems tight, but something going on.

Connected a 10 gage jumper from Battery Neg. to Right Alt. bracket and Battery
Voltage came up and matched Alt. output voltage @ 14.48 Volts.

Glow plug light problem gone, and Engine seems to Crank over a little faster.
Never realized cranking speed was slower than normal.

Volt gauge now at the tick mark in the green and stay's there no matter what I turn on.

Next step to remove Grounds from Battery to engine and check,clean, or replace.

Thanks
Tom

 

[cucvrus]

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Maybe not always 100% accurate. But I had that happen and it was a loose ground on the front battery post. Check and see if yours are clean and tight. Good Luck.

I posted this answer several times to this exact issue. I have had to self diagnose it after getting no response from the masses. Great Find.​