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1989 Bronco XLT, 351W, C6
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Discussion Starter #1
170379
So, my husband was driving my 89 FSB to get it painted and had an issue with the inertia switch. No problem, he jumped the switch and headed on down the road. About 5 miles out, he lose fuel pressure, engine stalls out, so on and so forth. He pops the hood and the jackets to the wire bundle at the starter relay are melted and the bare wire is glowing bright red.

Thinking there's a short, but how to trace it?

Also, where do I find the fusible links I would need to replace the ones on my Bronco?

Thanks in advance for your help.
 

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Yo CO,
FUSIBLE LINKS @:
NAPA
ADVANCE AUTO
ETC

Look for direct shorts to a GROUND FOR EACK FUSIBLE LINK

A, F, G, J, L, M, N, P, W & Y Location in Wiring Diagram in an 89; Fusible Link A-Brown 18ga to Rear Window Defroster; W-Blue 20g to Fuel Pump Relay; N-Blue 20g to EEC Power Relay; F-Blue 20ga to Trailer; Y-Blue 20ga to N.C.; L-Brown 18ga to ?; M-Brown 18ga to ?; G-Blue 20g to Exterior Lamps, Trailer; P-Blue 20ga to ?; & J-Green 14ga to Alternator
Source: by Seabronc (Rosie, Fred W) Rest in Peace Friend...



Parasitic Current Drain Test"...you should be able to trace the "parasitic draw" on the battery in the normal way. Pull the (-) cable off & put an ammeter inline set to the 10A range (or higher if possible) to see how much current is being pulled out of the battery with the key OFF, the doors SHUT, & the hood light bulb REMOVED. Make sure absolutely NOTHING is turned on anywhere on the truck. If it registers 0 or below the meter's next range, switch it down a range until it shows some useful numbers. If it ends up being below 0.5A (500mA), then replace the battery. If it's above that, start by disconnecting all the alternator wires & see if the reading drops under 0.5A. Then move to the fuse block & pull them 1 at a time until there's a significant drop in the reading. That's the circuit that's draining the battery. Follow it to find the problem..."
 
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Registered
1989 Bronco XLT, 351W, C6
Joined
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11 Posts
Discussion Starter #3
Yo CO,
FUSIBLE LINKS @:
NAPA
ADVANCE AUTO
ETC

Look for direct shorts to a GROUND FOR EACK FUSIBLE LINK

A, F, G, J, L, M, N, P, W & Y Location in Wiring Diagram in an 89; Fusible Link A-Brown 18ga to Rear Window Defroster; W-Blue 20g to Fuel Pump Relay; N-Blue 20g to EEC Power Relay; F-Blue 20ga to Trailer; Y-Blue 20ga to N.C.; L-Brown 18ga to ?; M-Brown 18ga to ?; G-Blue 20g to Exterior Lamps, Trailer; P-Blue 20ga to ?; & J-Green 14ga to Alternator
Source: by Seabronc (Rosie, Fred W) Rest in Peace Friend...



Parasitic Current Drain Test"...you should be able to trace the "parasitic draw" on the battery in the normal way. Pull the (-) cable off & put an ammeter inline set to the 10A range (or higher if possible) to see how much current is being pulled out of the battery with the key OFF, the doors SHUT, & the hood light bulb REMOVED. Make sure absolutely NOTHING is turned on anywhere on the truck. If it registers 0 or below the meter's next range, switch it down a range until it shows some useful numbers. If it ends up being below 0.5A (500mA), then replace the battery. If it's above that, start by disconnecting all the alternator wires & see if the reading drops under 0.5A. Then move to the fuse block & pull them 1 at a time until there's a significant drop in the reading. That's the circuit that's draining the battery. Follow it to find the problem..."
Thank you for this information!
 

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1989 Bronco XLT, 351W, C6
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11 Posts
Discussion Starter #4
Thank you for this information!
Traced the dead short to the 12v power line for the fuel pumps (pink/black). It was actually melted the full length of the chassis harness. I had another harness from a donor, so I swapped it out and replaced all the fusible links at the battery. I was concerned when the harness read continuity between the power wire and ground but realized that the pumps would read continuity so I fired it up. The fusible link for the fuel line started overheating again. Does anyone know what the impedance through each of the fuel pumps is supposed to be? The original high pressure pump (on vehicle when meltdown occurred) reads 2ohms--I replaced it for the donor which appears to have come from CarParts.com--the "new" pump reads 17.5ohms. I haven't checked the impedance across the in-tank pump yet, but if any of these values are too low, it might explain the over-amperage I'm witnessing at the fusible link.
Again, any help is greatly appreciated.
 

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Premium Member
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4,662 Posts
consider swapping to 92+ bosch style fuel, eec, and trailer relay. They are much better design and do not fail OFTEN like the brick nose and older.
 

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26,371 Posts
Yo CO,
Start testing at the fuel pump relay. Inspect for corrosion, wiring issues, etc
The relay must respond to the EEC processor and the relay contacts must be a low resistance path for fuel pump power.
Relay testing can be done in a couple minutes.
Fuel pump relay testing;
170726

Test at EEC pin 22 to check relay coil current draw.
Voltage at pump power terminal must be within .5v of battery power when relay is turned on with amp meter at pin 22.

Check power from battery if voltage is low.

Check the inertia switch and fuse if battery voltage is missing. DONE:cool::cool:

Pin 22- (light blue-orange; miesk5 Note, verify color) Grounded to turn "on". Voltage will drop to about 1v when "on". Current draw will be 160 to 270mA

Fuel pump monitor (dark green-yellow) 0v engine off, battery voltage with engine running..."
by member Dustball

170727


EEC IV PIN LEGEND BY RYAN M @ Ford Fuel Injection

Will try to verify wire colors.
 
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