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No power to ECM?

Bumper

New Member
Joined
Jul 16, 2010
Messages
42
Loc.
Learned, MS
I dont post on here often but I need a little help with this issue. Let me say that I am NOT a mechanic, but I am getting toward the end of what has been a pretty long project. But, in order not to bore yall with the details, I will get to the point. I have a 1966 Bronco. It has a Centech wiring harness. I installed an Explorer engine, a Ron Francis COBRA 75 EFI (MAF) harness. I have an MSD distributor with TFI and an A9L ECM from a Mustang GT. When I FINALLY attempted to start it up.....the engine turned over but didnt start....obviously. Thru very limited investigation into this issue, due to the fact that I must remain gainfully employed, here is what I know.

Fuel pump is not being energized.....I have no fuel in my fuel lines......I checked
I am getting no fire to the plugs

I SUSPECT that this is either because my ECM is bad, or I do not have it wired to the correct power supply. All my fuses are good.

The directions for the RF EFI harness speak to a group of wires that go under the dash and says the following:

Orange KEYED RUN Ignition Power Supply
Purple START Start signal for ECM
Green TACH Tachometer
Tan MIL Check Engine Check Engine Light Negative
Red MIL Check Engine Positive Check Engine Light Positive

So, my check engine light DOES work......my TACH does have power going to it.......so my thinking is that I dont have the Orange and purple connected to the correct place.

Both wires are landed on the BACK SIDE of the fuse box.....but I cannot tell for sure EXACTLY what they are terminated to as the fuse box is installed. I am going to ATTEMPT to access the box by taking the glove box out before I go thru taking the hood off and dropping the dash.

MY QUESTION IS......where do I need to land those two wires (orange and purple) on the back of that panel (or do I need to splice them into a wire and if so which one ) to assure that I get power to the ECM? I honestly do think the ECM is good....but I am NOT sure those two wires are properly connected.
 

Timmy390

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Jan 1, 2011
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5,609
Loc.
Conway, AR
Wire the orange and purple to the key/ignition switch. Fuse box = bad IMO. Off the top of my head I can't recall which wire is which at the ignition switch. Use a test light to see where you have power and hook them up (See below). I don't think power in "start" is anywhere but at the switch which trips the starter solenoid and power to the ignition

A) Connect the Orange wire marked “Keyed Run” to the keyed ignition switch hot wire. This wire must have +12 volts with the key in run and start positions.
B) Connect the Purple wire marked “Start” to the keyed ignition start wire. This wire must have +12 volts only when the key is in the start position. ***This circuit should only be hot when the key is cranking the engine. The intent Is that the system retards timing during crank to help the engine start up. If you connect this wire to always hot with key on you will experience an undesirable rev limiter at 2000-3000 RPM’s.

Fuel pump not running at key on.....could be related to the above. Rewire it and see what you get. Then if the FP is still not coming on....check for power at the relay then verify grounds, etc. Could also be a bad ECM

Tim
 

DirtDonk

Contributor
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47,355
The purple wire is already correctly connected because the engine cranks when you turn the key to start.

So check that the orange wire has power only when the key is in the on position. Not in the accessory position.
This is done by using the position on the ignition switch that used to be occupied by the red with green stripe, and green with red stripe wires.
 

DirtDonk

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If you suspect that they are already wired this way, then make sure that the orange wire has power in both on and start positions.
If the ignition switch is going bad it may kill the orange wire power in start.

But it sounds like it’s not getting power in either position, so check its connection and then check all the relays.

Does your engine harness have a bank of three or four relays under the hood? One of those is for power to the ECM.
 

Timmy390

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Loc.
Conway, AR
That harness has 4 relays and 4 fuses.
O2 and MAS relay A 15 amp fuse
Fuel pump is relay B 20 amp fuse
Coil and TFI relay C 15 amp fuse
ECM, injectors and IAC relay D 20 amp fuse

Tim
 
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Bumper

Bumper

New Member
Joined
Jul 16, 2010
Messages
42
Loc.
Learned, MS
If you suspect that they are already wired this way, then make sure that the orange wire has power in both on and start positions.
If the ignition switch is going bad it may kill the orange wire power in start.

But it sounds like it’s not getting power in either position, so check its connection and then check all the relays.

Does your engine harness have a bank of three or four relays under the hood? One of those is for power to the ECM.
Yes, I have that bank of relays. I am not saying that the relays are good for 100%.....but other than the three or four times I have tried to start it in the last few days, they have just been mounted to the fender and not connected to any power source. This build has taken me quite a while.......having kids, building a house, etc. have all made the project be last place for awhile.

I would also like to say that my ignition does not LOOK stock. I believe that the Centech harness had some type of adapter that plugged into the the stock ignition switch.....the wire that come out of it are not the colors that I have seen mentioned in other posts about ignition switches. I KNOW that there is a red, a black, and a white but will have to check on the color of the fourth one.
 
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Bumper

Bumper

New Member
Joined
Jul 16, 2010
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42
Loc.
Learned, MS
I was able to find the instructions for a Centech harness. I did not install the harness so I dont have them in any of my files. It looks like the harness came with a new ignition switch.....allegedly the four wires that come from it are red, black, white, and violet......if I can positively identify which one of those is KEYED RUN and connect the orange wire to it......then I should get the ECM in the game?
 

Timmy390

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5,609
Loc.
Conway, AR
The RF harness is a stand alone harness. It only has a coupe of wires that need to be tied into the Centech. It really shouldn't matter what harness you have for the Bronco. Mine is wired this same way with only the 3 connections listed below and it's a stock harness.

A) Connect the Orange wire marked “Keyed Run” to the keyed ignition switch hot wire. This wire must have +12 volts with the key in run and start positions.
B) Connect the Purple wire marked “Start” to the keyed ignition start wire. This wire must have +12 volts only when the key is in the start position. ***This circuit should only be hot when the key is cranking the engine.

The main power is wire 7 of the RF harness. Connects to battery.
Wire 9 is ground....I would check that...

Tim
 

Timmy390

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Loc.
Conway, AR
I was able to find the instructions for a Centech harness. I did not install the harness so I dont have them in any of my files. It looks like the harness came with a new ignition switch.....allegedly the four wires that come from it are red, black, white, and violet......if I can positively identify which one of those is KEYED RUN and connect the orange wire to it......then I should get the ECM in the game?
Use a test light to verify Keyed on and "hot in start" That's how I did it.

Tim
 

DirtDonk

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Also, if the Centech instructions did not come with the diagram, the Painless instructions do I'm pretty certain. That would show the back of the ignition switch and what each connector position does.

If your relays are not connected to power, nothing is going to work. Period...
There should be one single heavy gauge (probably 10ga?) wire that connects directly to the battery. Not the ignition switch.
There are four (one for each relay) smaller wires that get turned on with the key in the ON position. Because of their functions, they do not connect to the ACC terminal of the ignition switch. On a stock switch, this is the center stud.
On a Centech switch, you'd have to go by their instructions or do the light test that you two were talking about.

So does your ignition take a Ford key, or a small round one that looks like a generic small equipment key and switch?

Paul
 

Timmy390

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Did you check your inertia switch? Even if it looks like it pushed in, give it a smack and reset it.
I thought that too but the RF instructions don't mention there is one.

I use mine as a anti theft device. It's hidden 😀 and I just unplug it JUST enough

Tim
 

Jdgephar

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Sep 25, 2012
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I was able to find the instructions for a Centech harness. I did not install the harness so I dont have them in any of my files. It looks like the harness came with a new ignition switch.....allegedly the four wires that come from it are red, black, white, and violet......if I can positively identify which one of those is KEYED RUN and connect the orange wire to it......then I should get the ECM in the game?
Purple is start
White is 12V in run/start
Red is 12v battery (constant 12v)
Black is Accessory 12v

So, orange connects to white.

Sent from my SM-G981U using Tapatalk
 
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Bumper

Bumper

New Member
Joined
Jul 16, 2010
Messages
42
Loc.
Learned, MS
Also, if the Centech instructions did not come with the diagram, the Painless instructions do I'm pretty certain. That would show the back of the ignition switch and what each connector position does.

If your relays are not connected to power, nothing is going to work. Period...
There should be one single heavy gauge (probably 10ga?) wire that connects directly to the battery. Not the ignition switch.
There are four (one for each relay) smaller wires that get turned on with the key in the ON position. Because of their functions, they do not connect to the ACC terminal of the ignition switch. On a stock switch, this is the center stud.
On a Centech switch, you'd have to go by their instructions or do the light test that you two were talking about.

So does your ignition take a Ford key, or a small round one that looks like a generic small equipment key and switch?

Paul
Correct. There is a 10 ga wire that connects direct to the battery and it is connected. My ignition takes a ford key....I am not 100%, but I believe the centech harness came with an adapter that somehow "plugs into" the back of the original ignition switch. That adapter has the red, white, black and purple wires. BC Broncos and maybe a few others sell the adapter and I THINK that one comes with a Centech harness based on my research. I think the key to solving this issue is that orange wire........cant wait for a day off to find out which comes friday!
 
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Bumper

Bumper

New Member
Joined
Jul 16, 2010
Messages
42
Loc.
Learned, MS
Purple is start
White is 12V in run/start
Red is 12v battery (constant 12v)
Black is Accessory 12v

So, orange connects to white.

Sent from my SM-G981U using Tapatalk
I was guessing that the white wire was the one based on what info I could find, but I REALLY appreciate you confirming that. Now all I need is a day off!
 
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Bumper

Bumper

New Member
Joined
Jul 16, 2010
Messages
42
Loc.
Learned, MS
Did you check your inertia switch? Even if it looks like it pushed in, give it a smack and reset it.
That is something that I have not looked at or even thought about.......I will be sure to check that and be sure the button is PUSHED IN.
 
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Bumper

Bumper

New Member
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42
Loc.
Learned, MS
I thought that too but the RF instructions don't mention there is one.

I use mine as a anti theft device. It's hidden 😀 and I just unplug it JUST enough

Tim
There is an inertia switch......I am gonna make sure it is pushed in as well. Havent checked it, but will this afternoon or friday.
 

stretch

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Jun 15, 2005
Messages
449
Loc.
Montgomery, TX
Timmy,

Yea, I've installed two of the RF and one of the RJM, (same harness), and all three had and needed an inertia switch.

I recently walked out to start the rig after working on the wiring behind the dash, and had the same symptoms that Bumper described with on fuel pump but it would turn over. I had bumped the inertia during the work. Of coarse you go into panic mode and don't think of the easy things first. Took me an hour of trouble shooting to find it.
 
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