Can't locate a wiring diagram for 1987 Bronco with a carburated 5.

Hello;

I recently purchased a 1987 Bronco with a 351w run on a 4bbl carb. I am learning that it was an odd year in the series seeing that it was stock with a 4bbl carb. With that said, I am having an extremely hard time locating a wiring diagram for the Bronc. I am having an issue that all the gauges will lose power after the fuse blows anytime a decent bump is hit. I know there is a short somewhere and need to start tracing wires. Would love to have a wiring diagram to help out if anyone can link one up for me.

Thanks!

yo E,

Yes 87 did have the w/351W 4bbl carb

In VIN, Engine Code is H

http://www.lmctruck.com/icatalog/fd/full.aspx?Page=11

For now, this is all I have for the 87 and it does not specift if it is for carb or EFI in 87

Wiring Diagram in 87-89 Bronco & F series (Mitchell/Haynes); Source: by equivalent (Beetlejuice) at http://www.supermotors.net/registry/media/280828

many local library's offer free online access for their members; just log-in w/your library Card # and password

Our's went from on-line access to All Data (uses Ford's diagrams and info) for free but in-library use only; others offer Chilton or Auto Repair Reference Center Repair Manual, Mostly Chilton; incl. all Broncos, & many MAKES! 1951 to current; some years (85-Current, I believe) include: FULL Technical Service Bulletins and Recalls, Labor Hours per repair (plug in appl info); some Wiring Diagrams, Vacuum Diagrams (in DRIVEABILITY AND EMISSIONS CONTROLS Section), Specifications (torques, etc.) & Maintenance Intervals

Short Circuits

Troubleshooting with a Test Light (low resistance) General; "...The other way I use a test light is to check for short circuits. This test is done by putting the test light in place of the fuse. I use the small Radio Shack jumpers to do this. If you turn off all of the lights or loads on the circuit being tested, the light will go out when you have found the short, but it will light brightly while the short is still there...." READ MORE

Source: by Chris B at http://blog.rv.net/2008/10/tech-troubleshooting-with-a-test-light/

or

Troubleshooting with a Test Light (low resistance) General; "...low resistance test light can sometimes be used in place of a blown fuse. The light will illuminate while a short circuit to ground exists. DO NOT use a medium or high resistance test light in place of a blown fuse. These types of test lights illuminate with very small amounts of current and can be misleading..." read more

Source: by ocw.weber.edu http://ocw.weber.edu/automotive-technology/ausv-1320-automotive-electronics/10-trouble-shooting/short-circuit-detection

GL!

Thanks for the wiring diagrams. Between the diagrams and searching other topics in the forum I was able to get all of my gauges to work, except one. Seems that It was the pigtails on the alternator that was causing the fuse to blow to knock out all of the gauges. Everything is working except the fuel gauge, and I have hit a wall chasing that problem. It seems that at some point the previous owner had an alarm of some sort installed as I have found multiple wires under the dash T tapped, mainly the lights and various power wires. Looks like the Yellow/White sender wire for the fuel gauge was T tapped by mistake and just left. Time proved to cause the wire to break at the T tap so I started with the fuel gauge pinning past full. After some time searching I found the break and repaired it to now have it pin past empty. The weird part now, at least for me, is that the gauge stays pinned past empty until I hit the brakes, causing the gauge to then swing past full. Also the gauge will bounce up and past full if right turn signal is turned on (but not the left), as well as the hazards. I have been chasing wires under the dash and have followed what I can see of the sender wires back to the tank. At the moment I have had to take a step back to keep my sanity and wanted to see if anyone had any ideas on where to resume looking.

Thanks.

It sounds like a grounding problem at the rear of the truck. You are probably getting a back circuit through the sender to the gauge. The sender is grounded with the rear lights at ground point G100 which is located in the front of the truck. could be a broken wire or a corroded ground. It is a simple circuit, diagram attached.

The tail lights and sender ground all run on the same line from the rear to the front of the truck. I would suspect the ground line running to G100 is frayed or broken the lights are grounding through the fuel gauge so when you hit the brakes it puts 12V on the ground side of the gauge causing the pinning on E and F.

Good luck,



Sorry, having problems uploading pictures.

Seabronc said:

It sounds like a grounding problem at the rear of the truck. You are probably getting a back circuit through the sender to the gauge. The sender is grounded with the rear lights at ground point G100 which is located in the front of the truck. could be a broken wire or a corroded ground. It is a simple circuit, diagram attached.

The tail lights and sender ground all run on the same line from the rear to the front of the truck. I would suspect the ground line running to G100 is frayed or broken the lights are grounding through the fuel gauge so when you hit the brakes it puts 12V on the ground side of the gauge causing the pinning on E and F.

Good luck,

Sorry, having problems uploading pictures.

Click to expand...

OK here they are. Grounding in Bronco's stinks. On my truck I completely redid the grounding so it didn't depend on connections to the body or fenders.

My suggestion is to trace the black lead from the sender. Connectors are a high suspect. They corrode and often the wires break right where it goes into the connector.

If you have the opportunity, get an EVTM for your truck. It is the best troubleshooting book you can have in your back pocket. They often come up for sale on eBay. I did a search but didn't find one there right now. You could contact one of the sellers and ask if they have one that is not listed or to contact you if they get one.

Good luck,

Well... I finally found the problem. After cleaning up some of the caked on dirt from the ages I found that all of the wires that went into the harness connector, just before the wiring dropped down to the frame rail, had pulled back their insulation and started crosswiring. Fixed it all and finally have all my gauges and lights up and working again.

Thanks for the help.

From the looks of the wires, it looks like something got real hot at one time or another.

glad you found it.

Must be a common problem with that year.I had a 87 f150 with the same motor and the wiring did the same thing.