WTS light/ Glow plugs

Hi, For 5 months and the WTS light either flickers or doesnt turn on at all. Any ideas? Ive tested all the glow plugs they are good and ive replaced the connectors for the glow plugs. Ive also replaced the glow plug relay controller. Any Ideas? Im lost 100%. Thank yall

WhistlinDiesel said:

Hi, For 5 months and the WTS light either flickers or doesnt turn on at all. Any ideas? Ive tested all the glow plugs they are good and ive replaced the connectors for the glow plugs. Ive also replaced the glow plug relay controller. Any Ideas? Im lost 100%. Thank yall

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6.9 style controller or 7.3? FYI, 1987 6.9 has the 7.3 style controller.

It's on the fender away from the controller if it's the 6.9 system, it's behind the intake by the CDR on the 7.3 style with the relay on top of the controller. The relay can go bad either way.

I would check to be sure it's working. When they go, they won't activate the WTS light. When the one in my F250 NA was going, I had to bang on it with something non-conductive to get it to work. A new relay fixed the problem.

Regardless of the GP system, the relay is the same for all:

7.3 behind the intake. Im sorry, Im stupid lol. What do you mean bang on it?

WhistlinDiesel said:

7.3 behind the intake. Im sorry, Im stupid lol. What do you mean bang on it?

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The protective cover from the factory is usually long gone, with the posts exposed. Take a big screwdriver and bang on it with the plastic handle a few times, then see if WTS comes on. Something wooden would also work, anything that isn't conductive so you don't cross the terminals on the relay. If you have NA, taking off the air cleaner first gives you easy access. That's what I did until I got sick of doing it and replaced the relay.

Oh and I misspoke above, the relay is on top of the controller, not "controller on top of the relay". (I edited my previous post to fix the error)



The brown thing is the relay like I linked above, the black slab is the controller.

Here's a few more questions. You said that you did some testing and replacing, do the glow plugs work? They can work just fine and the light not work right. In your testing, did you ever test the wires that run to the glow plugs? They can get resistance in them. Are you getting enough power to the controller? A bad connection in the engine harness plug that usually is on the passenger's side inner fender could let enough current through to make the light flicker, but not enough to power the glow plugs. Does the controller click at all? Did you double check to make sure that the controller has a good ground (white wire)?

Well I replaced both controller and relay from diesel RX. The original one was clicking. Also I did put the ground where i found it (on top of the black slab) should I move it under or?? When I do the screw driver thig I should be hitting the posts?

The glow plugs appear to work fine and the lights does whatever the heck it wants. Although it doesnt seem like they work (I always have to keep my truck plugged in) The old controller did click but this one doesnt

WhistlinDiesel said:

The glow plugs appear to work fine and the lights does whatever the heck it wants. Although it doesnt seem like they work (I always have to keep my truck plugged in) The old controller did click but this one doesnt

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The 7.3 controller is solid state, it doesn't click. The relay is mechanical, that's what clicks. That's why banging in it can sometimes make it work when it's failing. If you don't hear clicking, you either have a bad relay or perhaps the wire leading to the ignition switch from the relay is damaged someplace. The relay must be working properly for the GPs to fire and for the WTS light to illuminate. The controller tells the relay to turn on and off, so if the relay is bad, nothing will actually happen. You'll hear no click, you'll get no WTS, and the GPs won't fire. At least with a cold engine. A full operating temperature engine can make it not activate at all because it's already warm enough.

WhistlinDiesel said:

Well I replaced both controller and relay from diesel RX. The original one was clicking. Also I did put the ground where i found it (on top of the black slab) should I move it under or?? When I do the screw driver thig I should be hitting the posts?

Click to expand...

It doesn't matter if you hit the posts, if you're using something non-conductive. You don't have to beat on it, just a few firm raps with something plastic or wood. Just enough to jar it inside so that it might trigger/activate.

I assume that when you say you checked the glow plugs, you checked their continuity?

Did you check continuity for the glow plug harness?

Did you check that you have a good ground on the small black wire?

Did you verify that you have 12v to one of the large posts on the GP relay? If you do, I would use junk screwdriver and jump across the two large terminals while checking the voltage there. The GP relay is fed 12v through a connector that is prone to failure. The pins get corroded, and eventually get hot and start to melt the connector. The connection may be good enough to show 12v with no load on the circuit, but then drop out when a load (like the GP’s cycling) is placed on it. It’s a pretty common problem.

That single connector wire...Cubey's photo above, upper left.

That wire connects to the WTS lamp in the instrument cluster. If the key is ON, the instrument cluster is powered up.

Grounding this wire ( the side going into the wiring harness ) should illuminate the WTS lamp. The engine does not need to be running to see this. But the key has to be ON.

The glow plug controller causes the WTS lamp to illuminate by internally grounding this wire.

You can verify that your glow plugs are cycling upon startup by watching your voltmeter and/or any incandescent lights when you are starting up. What you are looking for is the voltage drop on your battery when the glow plug relay switches the glow plugs on and off.

A good set of glow plugs will pull right at 200 amperes from the battery ( about 25 amperes for each plug ). It's effect when switched on and off the battery bus is quite noticeable, as the alternator is not yet spinning enough to bring the voltage regulator into play. This is also sufficient current to exaggerate the effects of corroded connections.

In my van, the WTS lamp is in a little cluster that very conveniently pops out from the front with a little prying along the edge, which makes bulb changes and electrical inspection a lot easier.

I zeroed in on the indicator circuit as you mentioned the glow plugs seemed to be working just fine, but the lamp had a mind of its own. But then mentioned you have to keep your truck plugged in.

What's the outside temperature?

Personally, I think you have either a grounding issue, or problems in the power delivery to the controller.

( Edited to remove crap. Note to self: post THEN have a beer).