Hello all, have a tough electrical problem to solve. I have an 88 F150 4x4. When to start it the other night and it ran for about 15 seconds and shut off. When retrying to start I notice no power to the interior dash instruments, radio, etc. But the headlights and key chime are working.

Ok figured I had a bad ignition switch on the column, changed it and have the same problem. Headlights work, light under hood works, key chime works, but no power to instruments or radio with key on. I can jump the solinoid post to the start terminal and the engine cranks.

I have checked all fuses. I even have power to the 2 posts labeled Batt in the ignition switch pigtail.

Where is the ground for the ignition switch and instrumentation?
Any suggestions on troubleshooting further would be appreciated. Thanks, Russ.

 

I think there are some fusible links of the battery (+) terminal
on the starter solenoid, check those.....

 

Turn the ignition to RUN and test the Wh/LB wire at the EEC relay or at the coil for 12V to ground. If it's 0V, check the R/LG wire at the ignition switch. If that's 12V, then you're gonna have to dig thru your wiring harness to find the Blue fusible link that joins the R/LG to Wh/LB. It's probably the coil going bad that blew it.

If the Wh/LB wire DOES have 12V, then try bridging the EEC relay terminal from Yel to the Blue wire. If that turns on the gauges, the relay is bad. Get one like this - they're much more relaible & cheaper than that old Ford style.

If that doesn't work, go down to the Red wire that the Blue leads to and jump THAT to the Yel. If that works, it's THAT Blue fusible link that needs to be replaced.

 

Thanks for the detailed post Steve83. I got some strange results though.
The test on the Wh/LB wire at the EEC showed 0V. Next I checked the R/LG at the ignition switch 0V too.

Now the strange part I retested the Yellow (batt) wires to the ignition switch to make sure my meter was working. With the ignition switch in the accessory or run position voltage is 0. Turn the Switch to off and they indicate 12V.

Maybe looking at a ground problem?

Thanks for your response.

 

There is too much resistance from a dirty or loose connection upstream from where you checked the yellow wires. No load(except your meter which is very little) and the resistance has little affect, letting most of the voltage through. Put a decent load on the wire(by turning the key on) and the resistance is too much, and the voltage drops.

 

Thanks for your reply. I cleaned the positive terminal at the solinoid, this is were the yellow wires start. There is one pigtail connector between the solinoid post and the connection at the firewall. I disconnected it and it looked ok with the white grease still there. After that point it connects to the firewall and goes behind the emergency brake, not looked in there yet. Whats behind there anyways.

1. How can I simulate a light load to see how far it is good down the line.

2. Does the interior, dash, gauges, etc. ground to a different point? Keep in mind I can jump across the solinoid and it turns over.

 

If you'd get the Haynes manual, you could look at the whole circuit and see how it works. You could also see where all the grounds are.

Use any 12V light bulb as a test load. A dash bulb for a small one or a headlight for a heavy one.

Did you test the fusible links at the starter relay yet?

 

Not sure what you mean by fusible links at the starter relay. If you mean the relays you discussed in your original post, no not tested or jumped because the power did not seem to be getting that far. If I followed it right, it went to the relays after going through the ignition switch and with the key to on I lose all voltage at the ignition switch. Thanks, Russ.

 

A fusible link is a specially designed wire that reacts like a fuse when there is too much draw on that circuit.
This wire is part of the wiring harness and connects to the battery side of the Starter Solenoid as mentioned.

You will notice a small rubber block that has the value stamped on it.

 

Got some new information. I got a test light and checked all the fusible links at the solinoid, all good. Followed the yellow wire down to a plugin with about 10 wires, still good past there. After that point it appears to go to a T looking connector on the firewall. I have NO power at the ignition switch with the load of the test light. The yellow wire at one of the EEC relays is hot and I believe a Black/Green wire at the relay was hot too. Is there another connection between that T connector at the firewall and the ignition switch? What is behind the emergency brake panel?

What to test next?

 

Hello all, I have an 88 F150 4x4 with a tough electrical problem. I had started the engine and it died on me very quickly. Ever since that I have no power to the dash instruments, but power to the headlights, interior light, key chime. I have tested all the fusible links from the solenoid (4 of them) all were fine. I can even jump the solenoid and make the engine turn over.
At the pigtail to the ignition switch I have NO power on the yellow battery terminals. A couple of fuses are hot still.

I have power to each EEC relay one was black/yellow and the other Yellow. Nothing else changes at the relay in any position of the ignition switch. There is one hot yellow wire going to the EEC behind the emergency brake.

Any ideas please, how can I narrow this down? Thanks, All.

 

Re-posted thread days after 1st

 

Bump of post. Need help troubleshooting. Does anyone know if the Yellow (Battery) wires at the ignition switch are powered straight from the solenoid or from the EEC relay or from the EEC unit itself. I have no power there.

 

It should be direct battery power from the starter relay thru a fusible link.

 

I have no detailed diagrams for your year truck. The latest I have is a fuel injected 1986 diagram. In 1986, it has 2 yellow wires feeding the ignition switch. Following these backwards, the two go into a splice. The splice splits the yellow wire in 3 directions, one going to the ignition switch(where we came from) and one feeds fuse f13 in the fuse box for the emergency warning flasher and the brake lamp circuit.

The other wire in the splice goes through the firewall somewhere, and does go to the starter relay. Looking at the diagram, it may be two yellow wires side by side going through the firewall, but it's hard to tell from the wiring diagram.

After the yellow wire(s) go through the firewall, the diagram shows several different optional ways the yellow wire is fed. One version takes the wire to what they call a "junction block". Some of the other versions seem to take the yellow wire through multiple fusible links. Studying the diagram, it looks like they have so many ways the yellow wire is configured because your truck may have:

An auxiliary battery option
Amp guage or idiot light
Fuel injection or carb

Whatever path the yellow wire takes with these different options, it always ends up right at the starter relay battery connection. Sorry, this is the latest diagram I have.