I was driving my '88 F-150 4.9L (300 c.i.d) yesterday when the engine just died, and I could smell that something electrical had burned out. I figured that the ignition module on the distributor had gone (again) - so I got one and replaced it. Well, that was not the problem (figures). Then I noticed that a wire coming off of the starter relay was burned off. I hooked them back together and when I hit the starter, it burned off again. Trouble is, it goes into the harness of the passenger side, across the front of the truck and joins the big mess on the drivers side. I checked Chiltons and the Alldata schematics, and neither address the individual wires coming off that realy. Where can I get a schematic so I can begin to troubleshoot? Or, if I describe the wire, can somebody tell me what the wire goes to so I can see what's going to ground? Thanks . . .

 

Well 88's are a little newer than any I have ever owned but I think the basic ignition eletrical is the same as the old 70's I have owned.
There are 2 small wires on the starter relay. The one on the "I" post is for the ignition on startup, it supplies 12 volts direct to the coil postive for starting only. The other on the "S" terminal gets 12 volts from the ignition switch to close the relay and turn the starter.
Which one burnt off? Either one could have burnt many other wires in the bundles they go thru If you are lucky you only have to replace the one that is burnt if not........
I suspect it is the "I" that burnt off. It may have been supplying 12 volts all the time to the coil, this may have been what has been killing your ignition modules.
Hope this info helps and is correct like I said never owned one of those "new" trucks.

Sparky

 

Well, there are three posts coming off the relay. One is for a small red wire going to the coil. That one is fine. The one that is burned is from a large post that has several wires coming off. Closest to the block is a large wire that goes to the starter. Next out is a smaller lt. blue wire that is [factory] spliced into two yellow wires - this blue one is the burned off one and also attached to the connector is a smaller green wire. Next connector out has two smaller black wires and the last connector out has a green wire going through a fusable link. I cannot tell where any of these wires go because they dive into a harness. The third and other large post comes from the battery. Hope somebody can tell me where the burned off blue [into two yellow] wire goes to.

 

I stand corrected Apparently the 88's are different then the late 70's.
Good luck in the faultfinding. Since I don't have any experience with those "new" trucks can someone else help!!

Sparky

 

Lets just double check. You have a starter solenoid with three terminals. If so One large goes directly to battery.One goes Directly to starter. The small(should be red wire) comes from ignition switch.
The only terminal that should have more than one wire is the one going to the battery.

 

Hello 88F150,

Well those wires going to the relay all head out to accesories of some kind. From your description the wire you are talking about may go to the alternator but i'm not sure without a schematic. You may have to physically search that wire to see where it goes.....yes I know that sux but without a good diagram you have no choice...I have had to do it myself many times in a shop. Try to peel back as much harness as you can to follow that wire but no more than necessary. I'm also surprised that you did not burn a fuseable link.

 

[updated:LAST EDITED ON 08-Jun-02 AT 00:21 AM (EST)]The original post is almost a year old

[font color=red]Dennis

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I have an 88 wiring diagram in front of me and you say the blue wire, the book says a green wire tied in with yellow wires goes to the armature in the alternator and to the B+ in the alternator. I would check them alternator plug ins and you will probably find they are burnt and your alternator is fried. My 88 did the same thing. There was a TSB on this same issue some time ago. They recomment that when you change out the alternator you change these plugs also. They are available at the auto parts suppliers. I got mine from Advance.

 

Thanks for all of the replies. I could not remember what user name or password or email address I'd used before, until I finally dug it out. Anyway, seems that the wire that burned off at the post, went across the motor and had rubbed on a head bolt and shorted out. Welded it's self. Anyway, it was found by luck, taped, re-routed and I've not had any problems since.

Thanks.

>I have an 88 wiring diagram in front of me and you say the
>blue wire, the book says a green wire tied in with yellow
>wires goes to the armature in the alternator and to the B+
>in the alternator. I would check them alternator plug ins
>and you will probably find they are burnt and your
>alternator is fried. My 88 did the same thing. There was a
>TSB on this same issue some time ago. They recomment that
>when you change out the alternator you change these plugs
>also. They are available at the auto parts suppliers. I got
>mine from Advance.