Inertia switch wires get hot!

[pacnwranger]

Hi Everyone!

Newbie here so this is my first post!

I have recently got a very nice '86 2.9 STX running after an engine swap. (The old engine was seized and the truck sat for several years!) Got it all hooked up, ran gas through the fuel system until clear and new and then set the timing. It starting up and was running well. After a few minutes I noticed a whiff of smoke from the right side engine compartment. It turned out to be the wires to the inertia switch. I jumped the connector and started it up, only to find that the jumper wire began to get hot. The short seems to occur only when the engine is running. I can leave the ignition in the on position and the jumper wire remains cool. (I'm thinking the inertia switch was stuck in the 'on' position.)

Again, the engine runs great, the fuel pump relay is good, and all the wires seem really clean and well-connected. My initial tests with a meter have all been okay.

Any help would be very much appreciated! Thanks so much!

 

[RonD]

Welcome to TRS

Congratulations on the 1986 2.9l Ranger

1985-1988 Rangers with fuel injection run TWO electric fuel pumps
A lift pump in the gas tank and a high pressure pump in the frame rail near fuel filter

So these years will tend to draw more AMPs(causes heat) than 1989 and up, that have just the one Fuel pump in the gas tank
Inertial switch is always closed(passes power) it should only open if its "jarred" like in an accident, which would cut the 12volts going to the fuel pumps
Inertial switch is in passenger side footwell of the cab, near the Computer

In the engine bay is a Fuel Pump Relay, should be plugged into a green base
EEC Relay has a brown base
WOT Relay has a black base, WOT relay is only used with Air Conditioning

So maybe you mean Fuel Pump(FP) Relay

The computer controls the FP relay and only turns it on for 2 seconds with key on, then it stays OFF until engine is started, its a safety thing
So no, the wires on that relay wouldn't get hot with just key on, not until they had power(amps) passing thru them, engine running, they would get hot, but NOT smoke hot

Fuel pumps draw 4 to 6 amps, so TWO could draw 8 to 10 amps
The fusible link(fuse) used in 1986 for the fuel pump power will be rated 20-25amps, and this will blow/separate if amps are exceeded, i.e. if there was a short

But you certainly shouldn't have seen "smoke" from ANY wire in a vehicle

It could be one of the pumps wires is corroded, which causes higher AMP draw, can be 12v or ground wire, or pump is starting to draw more amps, you can test the OHM on the circuit at the Fuel pump relay, should be no lower than 2 ohms

 

[pacnwranger]

Hi Ron!

Thanks for your reply. Yep, I'm looking at the relay with the green base. I tested the circuit, hooking up the meter to the connector, at what the fuse shows terminals #1 and #2 - the small terminals in the pic) and it comes out at 20 ohms.

Dave

 

[RonD]

Yes, that is the Fuel Pump Relay

Small pin slots in the base are for the Coil in the relay, these are used to activate it, slots 1 and 2

The one larger pin slot comes from fusible link should have 12volts all the time
The other larger slot goes to inertia switch in cab, and then to fuel pumps
Slots 3 and 4

Test which larger slot has 12v, don't need key on, it's hooked directly to battery positive via fusible link

Then use ohm meter on THE OTHER larger slot and to Ground, battery Negative is fine
That would show fuel pump OHMs

To jumper fuel pump to run all the time a jumper wire would go between the two LARGER slots(3 and 4), key on or off fuel pumps would run

DO NOT jumper the smaller slots

FYI, Stock relay is 4 pin but replacement relay can be 5 pin, the socket is made for 5 pin but the 5th pin is not used in this circuit/application
You don't need to replace it just a heads up

 

[pacnwranger]

Thanks again!

I get 12v from one of the large slots. I get no activity from the meter for ohms at the other large slot (and I did remember to change the setting on the VOM).

 

[RonD]

Meter stays at 1 or N/C(no connection) ?
Doesn't change at all

Touch meter tips together should see it changes to 0 ohms, if battery in meter is OK

Then retest

 

[pacnwranger]

Meter tests okay. But I get no indication or movement of needle. (It's not a digital meter.)

 

[Curious Hound]

Sounds like bad fuel pump or wiring. Fuel pump should have a low resistance.

 

[pacnwranger]

Thanks for your thoughts Eric.

Ron, I jumped the "big" slots of the connector and get nothing - no fuel pumps. Maybe there is a wire that I've mis-connected after the swap??

 

[RonD]

The 2 slots are top end of picture | and --

That should fire up the pump even with key off

So yes, something is disconnected

Battery(12volt)----fusible link----FP Relay------(green wire)----inertia switch-----(pink wire)-------fuel pump-----ground

 

[pacnwranger]

Disconnected indeed! I had forgotten to jump the inertia switch. Did that and now get results... 1 ohm for the fuel pumps and they do indeed come on when I jump the two big slots of the connector.

Am out for a few hours but will check back this evening. Thanks for putting up with me!

Dave

 

[RonD]

1 ohm should be OK, you are seeing the lowest resistance of the two fuel pumps

Did the jumper wire get hot, should be at least a 14gauge wire for the 15amps

 

[pacnwranger]

Started it again and ran it for a minute. The jumper, a heavier gauge, was okay. The leads to the connector got warm, but the blue wires to the solenoid (the uppermost two) were getting too hot to touch. Here's the pic...

 

[RonD]

Not seeing any "blue" wires, and only solenoid in picture has yellow and red wire

The starter relay maybe?
People do call is the starter solenoid
Those two "blue"/black wires are fusible links, could go to FP relay and EEC relay

Whats the orange jumper wire connecting?
Don't recognize that 2 wire plug

 

[pacnwranger]

You are correct... starter relay. Those two blue wires get very hot. Does this pic help clarify?