Strange 1986 Bronco electrical issue.

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Strange 1986 Bronco electrical issue.

Nickelplate
So, I am having a really strange electrical issue (or a couple of related issues) that seem to be centered on the Air Conditioning. There are two weird things that happen intermittently:

1. The 30A AC/heater/fan fuse blows out. This happens only sometimes and is a more recent issue. It only started happening after I got a new compressor. I put 1994 5.0 serpentine accessories on the front instead of the old V-belt stuff. I bought a brand new compressor, which is why I switched it out.

2. Whenever the AC selector on the dashboard is on MAX or NORM, the tachometer works differently (seems to just get stuck around 1000 and doesn't move), and the fuel, oil pressure, and engine temperature gauges all slowly climb. I replaced the gauge cluster voltage regulator with a new solid state one. Before I did that, the gauges would all climb to as high as they could go. After the replacement, they still climb but only partway up before they stop. I have experimented around with this and it seems like the gauges do not climb if the AC clutch is not engaged. As soon as I disengage the AC, the gauges will go back down to their real level.

Despite both of these things, when it works, the AC does work great, all fan speeds work, and everything is good.

Problem #1 only started a few weeks ago. Problem #2, I have noticed on and off since 2017. Problem #2 has persisted even though I have replaced: AC clutch, AC clutch wiring (from pressure switch to compressor), AC pressure switch, blower fan, blower fan resistor, blower fan speed selector switch in the dashboard.

My best guesses:

1. that something between the AC switch in the dash and the engine compartment has something messed up. In this case it is probably not the wiring itself, but the AC switch in the dash.

2. it could be that the diode in the engine compartment AC compressor harness is bad or does not need to be there now that I am no longer using the OEM ford ECU that it used to connect to. I am now using an Edelbrock Pro-flo 4 EFI system in it. I'm guessing it's not bad since it's brand new like the rest of the wiring, and maybe just doesn't need to be there.

3. the diode-containing lead that comes off the AC compressor and used to go to the ford ECU needs to be grounded? Right now, it's just hanging and doesn't connect to anything.

Does anyone know anything about what this could be? Anyone experienced it before? What are your thoughts?
1986 Bronco. 5.0L, Edelbrock Pro-flo 4 EFI, Baumann-controlled 4r70w, 3.55 gears, 31" tires.
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Re: Strange 1986 Bronco electrical issue.

Gary Lewis
Administrator
My guess is that you have a bad ground.  From the 1986 EVTM, the schematic below shows what circuits use G701, which is behind the left side of the radio on the firewall.  And everything you are talking about, and then some, use that ground.  So I think that when you bring the blower motor on, meaning not just A/C but Vent or Heater, the voltage on the ground comes up and that is messing up the gauges.

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

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Re: Strange 1986 Bronco electrical issue.

Nickelplate
Oh, wow! A lot of stuff uses that ground! I think I am familiar with that ground on the little rail that sticks out of the firewall there. Thanks a lot, I'll check it out and let you know!
1986 Bronco. 5.0L, Edelbrock Pro-flo 4 EFI, Baumann-controlled 4r70w, 3.55 gears, 31" tires.
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Re: Strange 1986 Bronco electrical issue.

Nickelplate
In reply to this post by Gary Lewis
I checked this morning, and it seems that the ground there is cranked down tight. When I installed everything, I scraped the paint off of the metal that it screws into. Might the problem be a bad connection between the body and the battery ground? I have the battery grounded to the engine block, the engine block also tied to the frame. But nothing but body bolts from the frame to the cab.
1986 Bronco. 5.0L, Edelbrock Pro-flo 4 EFI, Baumann-controlled 4r70w, 3.55 gears, 31" tires.
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Re: Strange 1986 Bronco electrical issue.

Gary Lewis
Administrator
There is supposed to be a ground from the engine to the firewall, as shown on our page at Documentation/Electrical/Grounds/Engine To Firewall Ground.  Without that there's very little to ground the cab and you will get all sorts of strange symptoms.
Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

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Re: Strange 1986 Bronco electrical issue.

Nickelplate
There used to be a ground there, back when I was using the stock EFI and the problem still occurred. However, I looked and saw that the ground from the firewall to the engine was not present. I put in a little extra work and ran a firewall ground from the same screw as G701, then along my custom wiring segment and straight into the battery ground.

I can't tell if the gauges issue still happens yet because I need to run the truck for a bit. But the "fuse blows when AC engaged" issue is still there. All fan speeds will work fine, but when the AC segment is added, it pops the fuse.

Any ideas on that one now that G701 is definitely grounded?

Another small bit of info, it doesn't immediately pop when AC is engaged, but waits 3-5 seconds.
1986 Bronco. 5.0L, Edelbrock Pro-flo 4 EFI, Baumann-controlled 4r70w, 3.55 gears, 31" tires.
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Re: Strange 1986 Bronco electrical issue.

Nickelplate
Also, just for search results for others who are looking into a similar problems, here is a link to the solid state voltage reg I got for the gauge cluster: https://www.dennis-carpenter.com/trucks/electrical/battery/d1az-10804-a-instr-cluster-voltage-regulat
1986 Bronco. 5.0L, Edelbrock Pro-flo 4 EFI, Baumann-controlled 4r70w, 3.55 gears, 31" tires.
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Re: Strange 1986 Bronco electrical issue.

ArdWrknTrk
Administrator
In reply to this post by Nickelplate
I'm looking at these two pages from the '86 EVTM






And thinking that if you have aftermarket engine management you probably don't have a TPS input spliced ahead of the pressure switch on the dryer.

I would definitely get rid of the diode and vacuum solepot shown with EEC.

Have you ohmed out the clutch field coil?
 Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.
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Re: Strange 1986 Bronco electrical issue.

Gary Lewis
Administrator
Yes, I'd get rid of the diode.  But I'd be surprised if it is blowing the fuse several seconds after the clutch comes in.  I'd have thought it would blow immediately.

So I'm with Jim that you need to check out that clutch.  It may be the culprit.
Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

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Re: Strange 1986 Bronco electrical issue.

Nickelplate
In reply to this post by ArdWrknTrk
Looks like we were all on the same page! I went through and tested in various conditions. It reliably blows fuses when the diode is installed. Also the diode gets wicked hot after the fuse blows. I'm sure that has to be it.

Thanks for the help, guys! Looks like the "fuses blowing" issue is taken care of.

The "gauges rising" issue is still slightly in play. I took these pics to illustrate. First one is without AC on, second one is with AC on. This is WAY less of a change than what used to happen, so I think the ground helped. But having a direct ground straight to the battery should have cured it entirely, right?



1986 Bronco. 5.0L, Edelbrock Pro-flo 4 EFI, Baumann-controlled 4r70w, 3.55 gears, 31" tires.
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Re: Strange 1986 Bronco electrical issue.

ArdWrknTrk
Administrator
I'm not sure about Carpenter's ICVR. I don't know anything about how it operates.
The factory one is basically a flasher unit.
Do you get pulsing current from your new and improved ICVR?

Perhaps the AC clutch thing is messing with its reference voltage or ground?

I only really know about the SWAD-J regulator mod that Gary has documented both here and on FTE.

 Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.
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Re: Strange 1986 Bronco electrical issue.

ArdWrknTrk
Administrator
In reply to this post by Nickelplate
I forgot to ask about your tach situation?
Was it helped with a new cab to engine ground?

Is there a way to program your EFI to step up the idle speed when the AC is operating?
I know the carb engines use a solenoid kicker throttle stop, but I know nothing about the aftermarket EFI.
 Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.
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Re: Strange 1986 Bronco electrical issue.

Nickelplate
Yeah, the Carpenter unit does give the same pulsed output as the old ones. Its main thing is that there are no adjustments needed like with the old ones.

The tach seems to be behaving better now that I have added the extra ground AND grounded that second post that switches it to 8cyl mode.

I'm not sure if this is just how they are supposed to work, but it hovers around 500 when idling (when it's actually at 800), then have to bring it up to actual 1000 before it budges from 500 and moves up and down with the RPMs. It is about 500 under what the actual RPMs are. I can see the actual numbers when I have my phone bluetooth-connected to the Edelbrock EFI ECU.

There is no way to let the EFI system know when the AC clutch is engaged, but it actually detects the slowdown and compensates for it. The compensation looks like a couple of surges while it "finds idle" and then evens out again around 800. It's pretty impressive.

Now that I got the fuse-poppin' issue taken care of, I should be able to drive the truck with the AC on and see how everything is working.
1986 Bronco. 5.0L, Edelbrock Pro-flo 4 EFI, Baumann-controlled 4r70w, 3.55 gears, 31" tires.
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Re: Strange 1986 Bronco electrical issue.

Gary Lewis
Administrator
Interesting.  Ford's EEC-V system has an input for the A/C clutch and I could up the idle speed immediately when the compressor kicks in.  However I like the 640 RPM idle even with the A/C on and didn't tell it to increase the speed.  But there's no bobble at all in RPM change when the compressor kicks in.

As for the tach, it sounds like it might be sticky, and/or need calibration.  Mine shows 500 when it is actually 640, but then is pretty close from there on.
Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

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Re: Strange 1986 Bronco electrical issue.

Nickelplate
I looked for an "AC to computer" wire when I installed the Edelbrock system. Turns out that they used to include one in the older versions, but it was causing folks a lot of problems to hook up. I think it had to do with some systems having the diode or a solepot, or a straight wire. The thing I read on the Edelbrock site said that in order to simplify the installation they removed the wire and updated the software for AC.

They do have a CAN bus connector on there, but I'm not sure if that could be used that way, and I know almost nothing about CAN.
1986 Bronco. 5.0L, Edelbrock Pro-flo 4 EFI, Baumann-controlled 4r70w, 3.55 gears, 31" tires.
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Re: Strange 1986 Bronco electrical issue.

Gary Lewis
Administrator
Ford used the same basic computer on everything from little 2.0L engines to my 7.5L, so needed some way to tell the computer when the additional load was coming on.

But I can see that some people might not understand the need for nor the orientation of the diode, so that could cause problems.
Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

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Re: Strange 1986 Bronco electrical issue.

mat in tn
maybe im off base here but what alternator is on this? you changed to serpentine so you had to change that also. what wiring mods were done?
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Re: Strange 1986 Bronco electrical issue.

Nickelplate
I have the Powermaster 200a 3g alternator right now. I have had a 3G alt on this thing for probably 15 years, but I had to switch to a transverse mount one with the new serpentine stuff.

The wiring is:
I have a 4 gauge charge cable with an inline 200A fuse that goes to a power distro lug. The power distro lug also has the battery positive, the starter relay/solenoid, and a few other power leads.

The alternator leads from the old 2G went to connector #610 which is on the passenger side fender well.
C-610
655 R-O - This wire is capped off
654 Y-LG - This wire is capped off
904 LG-R - This connects to the green wire from the 3G alternator harness
37 Y - This lead is the main power to the fuse panel and remains unchanged. It connects to that same power distro lug as the other big wires.

There is also the voltage regulator yellow/white lead from the alternator, which I have going to the power distro lug.

All the other wiring from the 2G alt is gone, which means my Ammeter in the gauge cluster does not work. I'm eventually going to convert it to a voltmeter.
1986 Bronco. 5.0L, Edelbrock Pro-flo 4 EFI, Baumann-controlled 4r70w, 3.55 gears, 31" tires.
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Re: Strange 1986 Bronco electrical issue.

FuzzFace2
In reply to this post by Nickelplate
Nickelplate wrote
Now that I got the fuse-poppin' issue taken care of, I should be able to drive the truck with the AC on and see how everything is working.
Did I miss what the fix was on the fuse popping was?

I have not looked into a issue I have on my 81 F100 (factory wiring / no computer) where when the AC compressor kicks on & off, be it low charge or temp, the dash turn signal lights flash.
You can only see this when it is dark, I leave for work between 12am & 4am, I do not see this in day light as the flash is to quick. I should also point out I have LED dash lights.

I know all my grounds are in place but being everything has been painted they may not be 100%and I need to check this someday.
It is not a big deal for me but just something that is along the same strange line with the AC as yours.
Dave ----
Dave G.
81 F100 flare side 300 six / AA OD / NP435 / 2.75 gear
http://cars.grantskingdom1.com/index.php/1980-Ford-F100?page=1
81 F100 style side 300 six/SROD parts truck -RIP
http://cars.grantskingdom1.com/index.php/1981-Ford-F100
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Re: Strange 1986 Bronco electrical issue.

Nickelplate
Yeah, the fuse pop was caused by the diode. It was no longer needed since the ecu was no longer attached. It was causing a short.

Your issue sounds like a ground as well. Though Reverse voltage through an LED shouldn't technically work.
1986 Bronco. 5.0L, Edelbrock Pro-flo 4 EFI, Baumann-controlled 4r70w, 3.55 gears, 31" tires.