Zen_Jones

I've been slowly fixing what I can on this 1988 F150. The vin says it's the 5.8, the DMV inspection sticker says it's a 5.0. Not real sure how to tell them apart. First things I've noticed, fuel gauge doesn't work. temp gauge doesn't work, I replaced both battery cables and the temp sending unit. Added a can of seafoam and filled the tank. Been trying to chase down the temp gauge problem, but I can't seem to figure that one out. After testing the temp sender by unplugging it and running it, I discovered the ECC at least recognizes if it is there or not, so it is getting a signal from it at least, even though the gauge isn't saying much.
Decided to try to track down the fuel gauge problem, Doesn't matter which tank I select, F or R, the gauge is pegged past F. Not sure how much fuel is in the R tank, but guess the F tank is 4-5 gallons shy of full now. In the process of tracking down the fuel gauge problem, I was trying to test the gauge by jumping a hot lead to the red with yellow stripe wire behind the dash, but in a momentary lapse (or possibly stupidity), I jumped that hot lead to the red with yellow stripe on the fuel select switch, it sparked, which I thought was strange, near as I can tell it should be a hot wire, which started a brand new problem, one that is more pressing than not knowing how much fuel I have, or how hot the engine is. Now the charging system is down. I've checked all the fuses and they are all intact, in retrospect I probably should have jumped from the other side of that fuse, maybe saved myself some hassle.
Tomorrow if I find some time, I want to take the alternator in and have it looked at. I checked the few fuseable links I could find, and they are all passing electricity. From the few wiring diagrams I have been able to locate, it appears that red with yellow stripe wire is a hot, and feeds back through the EEC, but I figure the EEC is ok, seeing as the engine will still start and run, I'm kinda hoping the ECC is ok as well, using the engine running as an indicator. I did do a reading just in case the volt gauge on the instrument cluster was acting up, and with 12.11 volts in the battery, with it running it dropped to 12.09, instead of jumping up to 14.8 like it was before. When I jumped that lead, the engine was not running, but the key could have been on or off, I don't recall. I am trying to figure out how jumping that lead could have affected the alternator and charging system. I am quite baffled, and still can't seem to locate good wiring schematics that cover in detail the wiring in the dash, instrument cluster, and under the hood. The haynes manual is about worthless, seeing as it seems to have a pretty serious gap in information especially on the '88 model. I especially love the diagrams that reference things that the manual doesn't cover. based on a complete teardown and rebuild, (of ones sanity perhaps...)
Anyhoo, if anyone is willing to help me tackle my nightmare, any and all help is appreciated. Thanks in advance everyone.

Aktech

There are two engine temp sensors one for the computer and one for the gauge.

5Rangers

As far as other schematics, specifically for which systems? As far as the temp sensors, like AK said, the one for the eec is at or close to the T stat housing, (Im a 4.9 guy) the temp gauge sensor is somewhere in the block.

Zen_Jones

The schematic you posted 5Ranger, is one of the ones I was looking at earlier, jumping the hot lead to the red/yellow stripe wire on the fuel tank select switch, trying to figure out why it sparked, and how it feeds into the charging system, along with why the charging system no longer functions. without a functioning alternator/charging system, it certainly makes all the other issues seem irrelevant in comparison. The schematic I need would be the one covering the alternator/charging system, and I guess some help locating the other temp sending unit. I will check the book a second time, but I did not see a second temp sending unit in it.

Just call me Sean

iTrader: (1)

Both are near each other, one in the thermostat housing one in the intake lower down. I think.

5Rangers

I am guessing you grabbed some wire from and unknown system and jumped to your fuel indication system? Which wire did you use. Color code? where it goes or comes from if possible. You saw it spark (was the key on or off?) and now it appears your charging system is not functioning? How do you know the charging system isn't functioning?

I'm thinking I must be half asleep because I ask so many questions, I'm like that in the morning until I have a few cups of coffee.

Edit: BTW, there are 7 charge and power distribution diagrams. So its helpful to know.

Another thought, if you take a hot wire and touch it to ground or a ground source, its normal to have a bit of a spark. Just like for example if you have your battery ground connected and touch the positive cable to the + post, you'll get some sparkage.

Zen_Jones

Actually, I took a hot wire from the fuel system, in the fuse box, from the supply side of the fuse on #15.

5Rangers

15 is used on diesel only to power the fuel selector switch, and the selector valve. Its a different setup then a gas fuel system. It should only be powered with the ignition switch in the run position. It should not have had any impact on the alternator.

So at this point your going to want to troubleshoot the charging system. How did you figure out it isn't charging? Edit... I read it.. you put a meter on and got 12 .. I would take it out and get it tested.

Zen_Jones

What is a good book to get that has all the wiring diagrams for the 1988 F150, with the 5.8 or 5.0 engine?

5Rangers

I have a set of factory books but I think there is an on line service called alldata.