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Ford F150 1998

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# 1  11/5/2009 3:36 AM

southLA
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Registered: 11/5/2009
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Ford F150 1998

Wind shield wipers, washer out and dome light, came back on for a week then out again. Have voltage up to relay. Ford F150 XL 1998 4.2L.

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# 2  11/5/2009 2:12 PM

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Re: Ford F150 1998

I checked out the schematic to see what the wipers/washers and dome light might have in common, and there's not a whole lot.

It looks like mostly independent switching, grounds and power sources.

They do share one common module called the Generic Electronic Module (GEM) or a Central Timer Module (CTM), depending on vehicle options.

I might be able to send you in the right direction if you can give me information as detailed as possible.

Are you sure that the dome lamp stops working at the same time as the wipers/washers?

Is it just the dome lamp on the roof, or also the courtesy lights in the doors that go out?

Does the dome lamp not work opening the doors, or when you turn on the dome light switch on the roof, or both?

This stuff would be a good start.


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# 3  11/6/2009 5:21 AM

southLA
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Re: Ford F150 1998

The dome light and there are two I guess map lights on each side of the dome light that you can switch off and on those don't work and the dome does not work when you open the door and if used the dash always on wheel the dome does not work. All dash lights work, head lights, turn signals, high beam work.

I have asked around and they are telling me it is the turn signal control which in the book it is called the Multi-function switch terminal and that should be the problem. Also I look at the Windshield wiper and washer system wiring diagram I do see something about Interior lamp relay. Thanks.

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# 4  11/6/2009 1:32 PM

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Re: Ford F150 1998

I still don't see much in common aside from the generic control module.

If you know how to use a test light, find the Interior Lamp Relay in the Junction Box Fuse/Relay panel.

Remove the relay and (with the ignition on) you should have 12 volts at relay terminal's 2 and 3.

When you turn on the Dome Light Switch there should then be a ground at terminal 1, which activates the relay.

If everything is correct at that point, jump terminals 3 to 5. That should bypass the relay and send voltage directly from 15 amp fuse number 14 to the dome lamp.

If there is no power at terminal's 2 or 3, fuse #14 is probably no good.

If there is power at terminal 3 but not 2, and jumping terminals 3 to 5 turned on the dome lamp, then you are not getting voltage from the Battery Saver Relay, which is controlled by the Generic Control Module.


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# 5  11/6/2009 5:15 PM

southLA
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Registered: 11/5/2009
Posts: 6

Re: Ford F150 1998

just what i was trying to avoid i changed the turn signal switch and still have the same thing. i will try what you suggest for the dome light but the wiper has three different relays, is there any thing common for those. Still the dome light and the wipers came back on at the same time once before so it seems there is still a connections between the two. Thanks.

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# 6  11/6/2009 6:27 PM

southLA
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Registered: 11/5/2009
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Re: Ford F150 1998

on the interior lamp relay i am getting voltage on 3 not 2 and jump from 3 to 5 the dome light comes on. Pulled and check the Battery Saver Relay I do have volts on 3 & 2. Thanks.

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# 7  11/7/2009 1:33 AM

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Re: Ford F150 1998

OK. On the Battery Saver Relay, you should have power at terminals 1 and 3, not 2. But if both relays are the same, I got a feeling the schematic is wrong...so you might be correct.

Terminal 2 (or 1) should be getting a ground from the Generic Control Module to activate the relay, and send power to the Interior Light Relay.

Pull the Battery Saver Relay and jump terminals 3 to 5. That should send power to the Interior Light Relay, and the lights should be working.

If they do, it's narrowed down to the Battery Saver Relay or the Generic Control Module.

If that's the case (and both relays are the same), pull both relays and put the Interior Lights Relay where the Battery Saver Relay was (don't mix them up). If the Battery Saver Relay was bad you should now be getting power at terminal 2 of the Interior Lights connector (which you didn't have before).

If you still do not have power at Interior Light Relay terminal 2, the Battery Saver Relay is not receiving an activation ground from the Generic Control Module.

I'm not going to tell you to replace the module, because they are expensive and there are several other factors which can prevent the module from doing its job correctly.

This is about as far as we can go. Not being there, I would be guessing at this point. You should really have a qualified technician (at the scene) who can use a scan tool and take diagnosis to the next level before condemning the module.

You're doing a great job.


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# 8  11/7/2009 3:51 AM

southLA
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Registered: 11/5/2009
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Re: Ford F150 1998

I did what you said and still nothing is the Generic Electronic Module (GEM) and the Multi-function switch (turn signal) are the same thing. Thanks.

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# 9  11/7/2009 3:34 PM

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Re: Ford F150 1998

The Multi-Function Switch is the directional switch in the steering column which also incorporates the wiper/washer control in the directional handle.

The Generic Control Module or Central Timer Module (Used only on 2-wheel-drive vehicles without power windows) is located left or center behind the instrument panel.

The signal from the wiper switch goes to the Generic Control Module. The module then turns on the appropriate relays to activate the wipers. The module also controls the courtesy lights and the activation of the Battery Saver Relay (which we were testing). Say you leave the doors open, after a certain amount of time the module will deactivate the Battery Saver Module to prevent the lights from killing the battery.

Like I said, I don't see a direct link between the multi-function switch (wipers) and the dome light, except for the module.

There may be trouble codes and/or input and output data viewable with the appropriate scan tool which may lead a technician directly to the problem.


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# 10  11/8/2009 7:15 PM

southLA
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Registered: 11/5/2009
Posts: 6

Re: Ford F150 1998

Thanks for your time.

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