Happy Holidays!

I recently picked up an ’88 F250XL 4x4 and am attempting to troubleshoot some electrical gremlins. I thought I was getting an authentic service manual with my truck but actually ended up receiving a Chilton and Haynes book which leaves a lot to be desired when it comes to schematics. As such, until I get a good reference manual I was hoping to enlist the assistance of the experts.

I currently have the following electrical problems:

1) I have no dash illumination. This includes the heater controls that I assume should be backlit.

2) None of the exterior teardrop marker lites on top of the cab work.

3) The radio dial indicator display works fine until you turn on the lights at which time it goes totally blank.

4) The 4x4 dash indicator lite goes on when the vehicle is in 2wd and off when it is in 4wd (i.e., it is reversed).


The previous owner indicated that he had recently replaced the dash cluster so, as a next step, I was going to pull this unit to see if I could spot any problems. Before I go thru the trouble of doing that, however, do these symptoms suggest that the problem might be elsewhere? For example, I checked the fuses (all were fine) and noticed that #4 is for dash illumination and exterior lights. Does this mean problems #1 and #2 could somehow be related? Also, if the problem was in the dash would that really affect the heater control lamps? I realize that none of these issues may be related but figured I would check.

This is my first Ford truck. Any advice / suggestions on next steps would be greatly appreciated. I need to get these problems fixed ASAP.

Cheers!

 

Umm, where to start? I would start with your headlight switch. It seems that 3 of your 4 problems have to do with the headlights in some way or another. See if you can troubleshoot it, or depending on how expensive it is, just replace it. I have no clue for the 4x4 since I don't own one of this vintage and don't know how it is wired. It seems like that could be a ground or something. I don't know if this thing is rust bucket or not, but it would be a good idea to check grounds on all these lights. A missing ground can do wierd things. Don't ask how I know that.

 

I agree w/77bigblock. Start with a headlight switch then check ALL grounds you can find, under the hood and in the dash.
Radios are strange things, somebody might have cobbled something in there once and screwed the whole thing up. I had a taurus that the radio only worked when the headlights were on when I got it, took several hours and a test light to straighten out what somebody would have only had to spend 5 bucks to avoid completely.

 

Are the cab lights a factory option? if not somebody possibly has cobbled them in. More than likely if you look under the dash you will find one or two scotch locks where someone has robbed power. I would look there first. Do the park and headlamps work properly?as far as your four wheel drive lamp, I would unplug the transfer case plug and see if the problem is still there. if not, you know where to look.

 

Thanks for the advice!

All the other lights work fine and, from what I can see, it doesn't look like there have been any add ons. The truck is also very solid having spent a good deal of its time in a garage.

The prior owner claimed everything worked fine until he replaced the dash cluster. I guess this confused me a bit cause I didn't see how this could have effected the other things. Sounded more like a headlite switch to me also.

Until I get my factory manual, is there someplace I can lookup the pin outs for the dash connections? Maybe they work like the old Christmas tree lites - when one goes out they all go out.. =)

Thanks again!

 

Here's how the ciircuit works for the factory cab marker lights. (Not aftermarket add on's).

Remove a lense from one of the Cab Marker Lamps and also remove the bulb.
Connect the black lead of your meter to the negative battery terminal. (Use a long wire or jumper wires).

When you place the headlight switch in Park or Head position 12 volts from a Brown wire from the headlight switch supplies 12 volts to the cab marker lights.

Take your red meter lead and measure the voltage at the center part of the socket. You should measure 12 volts. If you do, the lights aren't working because the bulb/bulbs are burnt out or you have a ground problem.

G909 is is the ground for the Cab Marker Lights. It's located inside the cab behind the lower left side plastic trim kick panel. (Area where the inside hood release is if you have that).

If you don't measure 12volts, you have a wiring problem from the light switch to the Cab Marker Lights. Can't be the Headlight switch because the same circuit provides 12 volts to the Parking Lamp exterior lights and the rear license plate.

If you turn the headlight switch off, change the meter to measure ohms and touch the red meter lead to the outer part of the bulb socket. You should measure zero ohms. If you read high resistance or infinity, the ground wire is bad.

The back lighting for the dash, heater, wiper washer switch, ash tray and radio all run off the same 12 volts that comes from the light switch. First make sure you turn the dimmer switch for maximum brightness. I believe that's alll the way counter clockwise. Going past that point turns on the inside cab courtesy light.

12 volts comes from the headlight switch via a Light Blue/Red wire and goes to fuse #10 a 5 amp fuse. 12 volts passes thru the fuse to the back light bulbs via a Light Blue/Red wire.

You need to pull the fuse and verify it isn't blown. The ground for all of the bulbs is from G701 which is a Black wire behind the center of the instrument panel. I can't see how that ground wire would go bad.

The trouble shooting of the 4x4 and 4x4 low light requires you to crawl under the truck and inspect the two pin electrical connector for any signs that Bubba has been working under there. The connector wires are Light Blue and a Light Blue/Black wire.

Depending on which Borg Warner transfer case you have, the 4x4 indicator switch is screwed into the transfer case near the front of the shift linkage or screwed into the tail shaft area of the transfer case.

If you place the transfer case shifter in 4hi the contact on the switch where the Light Blue wire goes should be grounded.

Placing the the transfer case shifter in 4lo the contact on the switch where the Light Blue/Black wire goes should be grounded.

 

Thanks! Just what I was looking for!

I'll do a little checking based on this info / advise before I go ahead and pull the cluster.

Wish me luck! It's getting too cold out here in the Northeast to be working outside on my truck. I hope its a quick fix (if there is such a thing).

More to come.......

 

Just to add another piece to the puzzle, when I went to fill both tanks up for the first time today, I noticed that the gas gauge also does not work. It remains pinned at Empty despite being full. The other gauges appear to work okay when the motor is running but I noticed that they don’t appear to reset properly (i.e., they don’t drift all the way to the left) when I turn the ignition off.

Is this sounding more like a ground problem? I was wondering if I could connect a jumper between a dash bulb ground and the frame to “manually” ground this circuit. I’m not an electrical guy but figured this might be a quick and easy test. There is an ashtray bulb that should be pretty easy to get to. Whatcahtink?

Have a great Holiday!

Cheers!

 

The guages are acting normal (except for the gas guage). The guages just stay where ever they were when you shut the truck off. If you turn the ignition back on, the oil pressure should bottom out, since you will have none.

 

This sounds like a bad ground, but I can't see how it might affect the clearance lights. Do any of the marker lights work, I.E. the tag lights, tail (not brake) lights, the front parking (marker) lights, etc?

 

The parking, turn, and headlites all seem to work okay. Maybe the cabin lite problem is unrelated. We had a bit of rain here yesterday and I noticed some water dripping thru the corners of the headliner. Perhaps the water is leaking thru these clearance lamps and has caused a problem somewhere.

Thanks to all for their help!

Merry Christmas!