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1985 Firewall Relay -- Pics added

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donaldb

1985 Firewall Relay -- Pics added

This post was updated on .

There is a silver metal housed relay behind the brake booster that has started buzzing. I looked through the wiring diagram but have not been able to find it. Anyone know what the relay controls? While we're at it, what is the black one control also.

Thanks

1985 Ford F150 XLT Lariat, 5.8W HO, 4BBL, 2wd, Long Bed, Red and Tan

grumpin

Re: 1985 Firewall Relay

I don't think you have in tank electric pumps, so I would guess the Trailer Lamp Relay.

Dane
1986 F250HD SC XLT Lariat 4x4 460 C6-Sold
1992 Bronco XLT 4x4 351W E4OD
1998 GMC Sierra SLE K1500 350 4L60E
Arizona

Gary Lewis

Re: 1985 Firewall Relay

Administrator

The trailer light relay shows in an illustration here: http://www.garysgaragemahal.com/trailer-option1.html.

Big Blue has the aux battery solenoid, which is the shiny unit in the pic below, as well as the fuel pump relay and the trailer lighting relay, shown to the right of the aux battery solenoid.

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

Steve83

Re: 1985 Firewall Relay

Banned User

In reply to this post by donaldb

donaldb wrote

Anyone know what the relay controls?

For all electrical devices, ID them by their wire colors. Post pics. The most-important wire (for ID) on a relay is the little one that triggers it to change state (on/off) since that identifies its function.

Rembrant

Re: 1985 Firewall Relay

In reply to this post by donaldb

donaldb wrote

There is a silver metal housed relay behind the brake booster that has started buzzing.

Behind the brake booster, do you mean on the firewall inside the cab?

What is the shape of the relay?

1994 F150 4x2 Flareside. 5.0 w/MAF, 4R70W, stock.
1984 F150 4X2 Flareside. Mild 302 w/ 5spd. Sold.
1980 F150 4X4 Flareside. 300i6 w/ 5spd. Sold in 2021.
1980 F100 4X2 Flareside. 351w/2bbl w/NP435. Sold in 1995

donaldb

Re: 1985 Firewall Relay -- Pics added

In reply to this post by donaldb

Pictures added

1985 Ford F150 XLT Lariat, 5.8W HO, 4BBL, 2wd, Long Bed, Red and Tan

Gary Lewis

Re: 1985 Firewall Relay -- Pics added

Administrator

I suspect the black one is the trailer lights relay. But don't know what the silver one is. We need to know what the wire and connector colors are going to both of those relays. And each wire should have a solid color and a secondary color, but you may have to uncover the wire from in a covering to be able to tell the colors.

Gary, AKA "Gary fellow": Profile

Rembrant

Re: 1985 Firewall Relay -- Pics added

Gary Lewis wrote

I suspect the black one is the trailer lights relay. But don't know what the silver one is. We need to know what the wire and connector colors are going to both of those relays. And each wire should have a solid color and a secondary color, but you may have to uncover the wire from in a covering to be able to tell the colors.

My 1984 FSM only shows two possible relays in that location.

Trailer Lights Relay:

Or the Marker Lights Relay, which was supposedly only on the DRW trucks:

However, that's from my '84 FSM...could be different stuff included in 1985 for sure.

Snagged this picture below from FTE, also from a 1985, and it was clicking, but the guy was trying to diagnose a no start issue, and the clicking silver relay was never identified.

That's my 2 cents while finishing my morning coffee. Not much help, I know.

85lebaront2

Re: 1985 Firewall Relay -- Pics added

Administrator

He hasn't said what engine he has so could it be the choke relay for a 351 4V engine? the 1986 EVTM shows a group of relays in the 5.8L 4V carburetor circuits but isn't clear on their locations.

Bill AKA "LOBO" Profile

"Getting old is inevitable, growing up is optional" Darth Vader 1986 F350 460 converted to MAF/SEFI, E4OD 12X3 1/2 rear brakes, traction loc 3:55 gear, 160 amp 3G alternator Wife's 2011 Flex Limited Daily Driver 2009 Flex Limited with factory tow package Project car 1986 Chrysler LeBaron convertible 2.2L Turbo II, modified A413

Gary Lewis

Re: 1985 Firewall Relay -- Pics added

Administrator

I had wondered that as well, but there appears to clearly be a black/yellow wire in the pic and I can't find it in any of the EVTM illustrations I've looked at. Here's the carb ones:

Gary, AKA "Gary fellow": Profile

Rembrant

Re: 1985 Firewall Relay -- Pics added

In reply to this post by 85lebaront2

I think Lebaron nailed it...

If you do a search on choke relay, a couple different old threads pop up, and they're all in reference to a 351 4bbl engine...

Pics of the same relay in this thread below:

https://www.ford-trucks.com/forums/1146787-carb-choke-problems-2.html

donaldb

Re: 1985 Firewall Relay -- Pics added

Interesting, the factory carb has been replaced with a regular Holley, requiring 12v for the choke. The relay in question I would guess with pretty good confidence is factory since it is using the same color and shape rivet to hold it on as the other one. If it warms up in Missouri today I'll see if I can get the wire colors.

Thanks all who commented.

1985 Ford F150 XLT Lariat, 5.8W HO, 4BBL, 2wd, Long Bed, Red and Tan

Gary Lewis

Re: 1985 Firewall Relay -- Pics added

Administrator

In reply to this post by Rembrant

First, what do those yo-yos on FTE know?

Oh wait! I recognize some of them.

Ok, so it is probably the choke relay, although there does seem to be some discrepancy with the wire colors - both in the FTE thread as well as here. Further, the EVTM contradicts itself. The schematic above is from the 1985's page for 5.8L carb circuits in the Electronic Engine Controls section. Note that it says the connection goes to Page 15. The schematic below is from Page 15, and it clearly says only the 4.9L engines have a connection to the carb circuits on the Electronic Engine Control page. All else go directly to the choke. Hmmm, can't be both ways.

But, let's assume that's what it is. Then why is the relay buzzing? I'd say there's a problem with the alternator's stator output. If you look at the schematic you'll see that the stator isn't grounded, and that it relies on the diodes. I think one or more of the diodes are blown.

Gary, AKA "Gary fellow": Profile

donaldb

Re: 1985 Firewall Relay -- Pics added

Gary think you are right about the diodes. Is the diode set replacable on Gen 1 alternators?

Thanks

1985 Ford F150 XLT Lariat, 5.8W HO, 4BBL, 2wd, Long Bed, Red and Tan

Gary Lewis

Re: 1985 Firewall Relay -- Pics added

Administrator

Yes, it is. But you might want to upgrade to a 3G.

Gary, AKA "Gary fellow": Profile

vjsimone

Re: 1985 Firewall Relay -- Pics added

This post was updated on .

In reply to this post by donaldb

donaldb, photo those wires and connector if you can.

Vinny... "Do All Scheduled Maintenance Prior To Troubleshooting" "Resolve All Known Issues Prior To Troubleshooting"

donaldb

Re: 1985 Firewall Relay -- Pics added

Finally warmed up to get out there and look at it. It is exactly as Gary's wiring diagram shows above. 2 black ground wires, Yellow, gray with with white, and white with black.

Thank you all for the help
Donald

1985 Ford F150 XLT Lariat, 5.8W HO, 4BBL, 2wd, Long Bed, Red and Tan

Gary Lewis

Re: 1985 Firewall Relay -- Pics added

Administrator

Welcome. Have you figured out why the relay was buzzing?

Gary, AKA "Gary fellow": Profile

donaldb

Re: 1985 Firewall Relay -- Pics added

As you said alternator.

1985 Ford F150 XLT Lariat, 5.8W HO, 4BBL, 2wd, Long Bed, Red and Tan

Gary Lewis

Re: 1985 Firewall Relay -- Pics added

Administrator

In reply to this post by Gary Lewis

And, more specifically, blown diodes. That would give alternating current to the relay's coil, causing it to alternately pull in and then drop out, creating a buzz. Thanks for confirming the theory.

Gary, AKA "Gary fellow": Profile