Tracking down an electrical bug....

[Darel]

'86 BII 2.9/FM145/4x4

Chasing an electrical gremlin, kinda thinking one of the circuit breakers in the fuse panel but I could be wrong. While driving, I lose power to a very specific set of accessories intermittently. Power always returns within a second or two, which is why I'm thinking a weak circuit breaker (NOT FUSE). At first I thought it was just the radio cutting out, but then I realized it was a couple more things all at the same time. Here's what I've been able to determine cuts out, again just for a second or two intermittently while driving:

• radio cuts out and light on display goes out (but NOT the clock, and I do NOT lose presets - clock stays on dim display)
• Wipers, stop dead (haven't managed to catch it with the rear wiper on yet so I don't know about that one)
• temp gauge
• fuel gauge (on the center console warning center, the "low fuel" light will come on when the gas gauge cuts out)
• No lights are affected, headlights, blinkers and dome light continue to function fine. Heater blower fan continues to run.
• On the console message center, my "washer fluid low" light is always on. When the power loss happens, this light goes out. It's the only time this light is ever out.

The way it behaves, cutting out and coming back in just a second or two, I am thinking a weak circuit breaker tripping and resetting. However I do suppose it could be a loose wire somewhere. Does anyone know a junction where all these items come together? It's not the ignition switch because then I'd at least lose the blower fan too.

Thanks,
Darel

 

[Curious Hound]

I really don't think you have a circuit breaker for those things. This reads like a loose connection somewhere. There are some electrical diagrams in the "how to tech" section of this website that should be close enough to troubleshoot this. Just follow the link at the top of the page or in the menu.

If I get a chance later, I'll look at them and see if I can help point you in the right direction.

 

[Darel]

Thank you. I'll try and trace some of that out. It's also been suggested a fusible link or the ignition switch, but the accessories that actually stay on while the rest of the stuff cuts out kinda tells me its' neither of those. I would have thought ignition because it does seem like mostly the battery-hot stuff stays on while the ignition-hot stuff cuts out, but the fact that the blower fan keeps running has me stumped. If it was the ignition switch the fan would go out, if it was the fusible link everything would go out.

 

[Darel]

Went through all the diagrams on this site. Couldn't find anything for accessories. Everything was engine and lighting, and a couple very specific systems (power door locks etc) but none of that is ever affected. I went through the diagrams anyway and still didn't find any of the systems that are affected. I have a Chilton book at home, I was assuming that didn't have good wiring diagrams in it but I should check when I get home.

 

[Uncle Gump]

When things like this happen... it is kinda overwhelming wondering where you should start.

Seems to me the one common spot that all these systems come together is going to be the ignition switch.

 

[Darel]

It wouldn't be all that overwhelming if I could find one wiring diagram that had more than one of these systems laid out on it. I can't find a single diagram anywhere that shows the power feed for the radio, or the feed for the minor gauges. Thinking is the wipers are the most telling, and they come right off the fuse box. However, I don't think it can be the ignition switch because the blinkers still work, and the blower motor. And the truck continues to run just fine, never stutters or anything. I do have the feed for the wipers and a full diagram coming off the fusebox, but that's not all that helpful.

I think my first course of action is going to be to check out the back-side of the fusebox.

 

[Uncle Gump]

That is your choice... but tell me... where does fuse block power come from for the wipers? And power for all things you say drop out?

Short answer... Ignition Switch

Edit... You say all these things drop out and come on together. So that tells me most likely you are looking for a single point of failure.

 

[RobbieD]

One more thing to check. Look closely at the ignition switch. The plastic base part, where the wiring harness connector plugs in, can come a little loose from the metal body, that is screwed to the steering column. I've had this problem before, and running a good-sized tie-wrap around the switch can fix it, or just replacing the ignition switch. Good luck, and let us know what you do find.

 

[ford4wd08]

Look at the ignition switch in the column, where the blocks slide against each other to make contact and complete the circuit. I believe the '86 is the same as the '85.

I had a no start issue, were in the start position it was making contact and the starter would work and engine would run, but as soon as I moved it back to the the run position, it would kill everything. None of my accessories worked during this time.

I would take it apart and clean the contacts and reassembly and see what happens.

 

[Darel]

OK thanks guys. I will try and get out there today or tomorrow and check it out.

 

[Darel]

Well, I guess it's my turn to eat crow. My ignition switch was coming open slightly on one side exactly as pictured above. I could wiggle the column up and down and cut out the power to the accessories at will. Ziptie fixed it. Thank you guys very much!

 

[Uncle Gump]

Nice... glad you found the problem.

 

[RobbieD]

Don't beat yourself up over it. The ignition switch coming apart is kind of common, but if you don't know what to look for it's real easy to miss.

Thanks for letting us know what you found, and good to hear that you fixed it.

 

[Curious Hound]

Excellent. Good job.