Electrical Mayhem, Help Needed

[crash-harris]

I could do that, though I doubt I'll have constant power (very possible though). I'm not really thrilled with the idea of leaving the key on even long enough to poke around with the multimeter. If I'm having such a dibilating short that is kicking everything on and off rapidly (while the relays are trying to stick on), and burnt a 18ga wire (smallest I have to jumper it is 14ga), it's very likely that something else in the circuit will burn through instead, leaving more problems to find. I really do not enjoy unbolting the radiator and stripping the wiring of its tubing and 25 year old electrical tape all the way around the front/sides of the clip.

The other yellow wire with the 20ga fusible link connects to the igntion switch from the looks of it.

 

[laserjock]

I go back to if the fusible links in the engine harness burnt, it's just about got to be a problem with either the alternator or gp controller that caused that. Unhook all that and see if it behaves. Add things back one at a time. It really shouldn't be that complicated. To sort out. These trucks are pretty simple. Obviously grounding is a problem too.

You could have several problems but cross the easy things off the list first.

Your reading of 14ohms across the cables could just be you reading through a bulb.

If the big things check out, when I'm trying to find an electrical problem, I hook the meter up inline as an ammeter and start pulling fuses looking for a change in behavior. These trucks should have less than an amp parasitic draw. Note, if you do this, do it with the gp controller unhooked and nor cranking because hitting the key would smoke your meter.

Process of elimination. Eliminate the easy things first then dig deeper.

 

[crash-harris]

I have pulled anything and checked yet, so I will disconnect the constant hot to the GP controller and then the alternator after we get back from the parts store tomorrow.

The black and orange charging wire from the alternator to the starter relay is the one on top of the alternator that's no longer connected. Whomever redid the battery cables also ran a larger cable in its place.

 

[LCAM-01XA]

Anything on those 4 cut off wires? Some of them seem to go to this relay socket.

The four cut wires are most likely for a factory trailer brakes controller. IIRC the black is your constant battery feed, the red one is trigger from the brakes switch on the pedal, blue is power output to trailer brakes, and orange is brake lights power for trailers with separate brake and turn signals (uses the 7-way round-pin connector common for older agricultural trailers). The black wire is fed by a single 20-gauge fuse link that IIRC does in fact start as yellow near the starter contactor on the fender and then in a typical Ford fashion changes color across one of the connectors (try keeping up with those random color changes on a E4OD-equipped truck, your head will spin). I'm thinking your burned fuse link is the one for the factory trailer brake controller, see if any of the cut wires are hot with the fuse link jumped, and if that goes away when you remove the jumper.

Regarding the relay connector, in a '89-'91 IDI truck there are only two things that have relays in that location - the E4OD transmission and the factory towing package for the trailer running lights. If you have a stick-shift then you don't have the E4OD-related wiring, meaning the missing relay was at some point powering the running lights circuit for the factory trailer connector. Which jives well with the 4 cut wires matching the colors of those used in the factory trailer brakes controller. And in case your truck is a dually the trailer lights relay will also power the four small marker lights on the rear fenders and the three small "ICC" lights under the tailgate. The circuits are actually decently set up and with proper gauge wires, however many owners chose to bypass them and run their own due to not having access to the factory wiring diagrams. Back in the days internet was as easily available, and knowing Ford's general assholiness (they have forever lost any respect I may have had for them when they shut down OldFuelInjection.com) I kinda doubt factory EVTMs were commonly found in public libraries...

 

[crash-harris]

I read the diagram wrong. Either it's the wire to the ignition switch, or the black/orange wire to fuse 16. I'll check those after the alternator and GP controller in the morning.

 

[franklin2]

I think the main difference in our troubleshooting methods comes from a difference in our thinking of what's wrong. The theory you are going on is that something is shorted, pulling down the electrical system and making it blink on an off.

My theory is that there is a bad connection or poor cable somewhere in the line that is causing it to "starve" the system for power.

In my experience if there was something shorted in the system, it's not going to pull it down till it goes off. The batteries have enough power where they are going to smoke something before they give out.

Let's say you did have a short in the line that is fed from that fusible link that was burnt. If you had a short in that line and replaced the fusible link or just wired it directly and then hooked the batteries back up, the system would not blink on and off again till it burned the link or the wire. That wire or fusible link would start smoking immediately.

Keep going, you will find it eventually whatever it is. I hope you are not in a hurry to get it fixed, it goes better if you are not under pressure to fix it.

 

[IDIoit]

FWIW.
when i think i have a short somewhere,
i disconnect the batteries,
get access to the fuse panel,
and use an OHM meter from the ground to the IN on every fuse.
if you have a short, this will help you track down whats shorting.

 

[typ4]

Ok, here is how I would start this whole thing.

Get the big ground cables to the engine block.
Make sure there is one at least from block to frame.
There should be one also off the battery neg that screws to the core support, another for a harness ground.
Unhook all battery hot truck feeds from starter relay. Inc alt hot
Hook up batteries.
Key off, start touching feeds to battery hot, maybe a jumper cable hooked to battery so things dont get arc damaged.
Then start turning things on, headlights ,so on and then Ign switch, do it all again.
Leave GP feed off for all testing. I think it is clicking andd drawing power thru some loose connection and dropping truck power
As I said before, cut out all crap PO wiring.
Fix headlight connector, that box you found is the wiper delay.
If this truck has RV plug, maybe the battery feed was somehow tied to the wire that burned.
Dont get fixated on adding grounds till the original style is in place.
You have to have a short/overload to burn wires, floating grounds wreak havoc with accessories.
Print this, check it off, good luck.

 

[crash-harris]

I think the main difference in our troubleshooting methods comes from a difference in our thinking of what's wrong. The theory you are going on is that something is shorted, pulling down the electrical system and making it blink on an off.

My theory is that there is a bad connection or poor cable somewhere in the line that is causing it to "starve" the system for power.

In my experience if there was something shorted in the system, it's not going to pull it down till it goes off. The batteries have enough power where they are going to smoke something before they give out.

Let's say you did have a short in the line that is fed from that fusible link that was burnt. If you had a short in that line and replaced the fusible link or just wired it directly and then hooked the batteries back up, the system would not blink on and off again till it burned the link or the wire. That wire or fusible link would start smoking immediately.

Keep going, you will find it eventually whatever it is. I hope you are not in a hurry to get it fixed, it goes better if you are not under pressure to fix it.

Unfortunately I am, as always. I feel a bit redneck with 3 trucks that can't move. The CC due to this problem, the SC due to rusty frame/brackets and worn rings, and the bronco due to no floor, exhaust and rusty radius arm brackets. I could've gotten the wooden part of my fence done this weekend if I didn't have to get this fixed and I so have about 300-400 feet of t-posts and wrote fence to do yet. Working 2nd shifts, I'm out of the house for 11-12 hours a day and can only work on most things over the weekend, if the weather cooperates. It's all done seriously bad timing.

 

[crash-harris]

I think bad a bad connection/bad ground did cause the problem though, but I think developed into a short. I get continuity between the positive cable while disconnected from the battery and the body.

Just got home with 2 battery cables for engine grounding and a strap for the body. Couldn't find fusible links, so I just got more 18ga wire.

 

[laserjock]

Everybody trouble shoots differently. Take your time work through it methodically (whatever path you take) and think about what the tests are really telling you. You'll figure it out.

 

[typ4]

If using a meter you will have a reading between battery cable and body, alt, bulbs, or a short.

 

[madpogue]

Couldn't find fusible links, so I just got more 18ga wire.

That'll tide you over for now, but remember, your fusible links are your protection from a serious electrical problem starting your truck on fire. Another option would be to convert to maxifuses in place of the fusible links, using a multiple fuse block. One thing I've been searching for, and I'm sure is out there somewhere, is a translation table that translates the gauge number of the old '80s vintage fusible links to current capacity, so as to know what rating of maxifuses to use.

 

[fsmyth]

Good first step.
Get some fuseholders. Use those in place of your fusible links. Now you can control
how much current you are feeding the various circuits while troubleshooting.
A 10A fuse is a good starting point. If that blows immediately, then you definitely
have melted wiring or melted switches somewhere.
You can use a 12v tail lamp bulb in place of the fuse for safely limited current for
testing. When you have found the problems, use a 30A fuse. Should be ample for
replacing the link you removed. If not, just step up until it stays, then add 5-10A.
(I actually use an ammeter, turn everything on, and fuse for an additional 5A).
Get everything grounded properly. Look carefully for all the smaller 18-12 ga. wires
going to the body. Ensure the BODY is grounded to the frame. Ensure that the
frame is grounded well to both batteries. It sure sounds like you still have a
floating ground somewhere.

 

[crash-harris]

That's what I did with Bruiser (the gasser '90). I have a 35 amp breaker, a 20 blade fuse and a 10 amp blade fuse.

But, I am conceding to the lack of proper grounding being the ENTIRE problem


Just finished putting on the new grounding cables and strap. Turned the key and discovered constant, normal power. Just started 'er up too! Now I'm going to replace the 18ga fusible link with the 18ga wire I brought home and replace the headlight switch connector for good measure and take her down the road and back.

Thanks a bunch guys!