72 bronco instrument light fuse

[bigdog137]

Hey everyone, a quick question. I have a stock 72 bronco, recently replaced stock switches and wiring harnesses with the stock replacements. Now I have a few electrical issues i am trying to sort out. One is
that #3,,,2 amp fuse does not light up, on either side, with a test light until I pull the headlamp switch to parking or headlight mode. This cant be right, is it? So, the test light on the #3 fuse, nothing. Pull the headlight switch out, it comes on. I am having issues with my Instrument voltage regulator also, but one thing at a time. Is it possible I have a bad headlight switch?
thanks in advance for any advice.

 

[DirtDonk]

It is correct that the fuse gets no power until the headlight switch is pulled to at least the first position.
That fuse is the only one on a separate circuit in the panel, and protects the instrument lamps only.
It’s correct because the lamps are only supposed to come on when the headlight switch is pulled.

 

[DirtDonk]

The instrument voltage regulator gets its power from the Black w/green stripe wire directly on the back of the ignition switch.
From the switch it goes into the main harness and then branches off from a splice to the regulator.

What is the actual problem you are having with the regulator? And what problems were you having that prompted you to change some of the other components and switches?
Did you keep the old ones? It’s not uncommon for brand new parts to be defective right out of the box, or within a short time.
So if your old ones were not actually failed, best to keep them as spares.

 

[bigdog137]

The instrument voltage regulator gets its power from the Black w/green stripe wire directly on the back of the ignition switch.
From the switch it goes into the main harness and then branches off from a splice to the regulator.

What is the actual problem you are having with the regulator? And what problems were you having that prompted you to change some of the other components and switches?
Did you keep the old ones? It’s not uncommon for brand new parts to be defective right out of the box, or within a short time.
So if your old ones were not actually failed, best to keep them as spares.

Hey, thanks for the information. The IVR gets real hot, too hot to touch. I am getting the full power on the hot side and reduced power,,5 amps on the other. I start it up, the temp and fuel gauges peg, the oil seems to read about right. Then they all go dead, back to zero. I have tried several IVRs, but now realize they aren't the problem. I get the 5 amps at the output side of the IVR, but strangely nothing at the water and oil sensors under the hood. I've tried grounding them with nothing moving the needles inside. I have installed an additional grounds for the dash body etc. This was a plug and play harness from Dennis carpenter. I started out just doing 1 loom at a time, then, the next thing I knew, the entire wiring system. I did do the 1 wire alternator upgrade, but it reads out well and i cant see how that would effect this. I have driven around with the IVR unhooked and no problems other than no gauges.. If I don't figure it out i will drive it like that a few times then tear it down again this winter. Thanks for any advice you can throw at me.

 

[DirtDonk]

Hmm, odd one for sure. But I bet someone here will know intuitively what's going on.
A hot IVR is not right, as you suspected. Seems like a defective unit, but are they all acting the same as the original one you pulled out? Or was the original long gone already?
The gauges pegging upon initial turn of the key is wrong for our rigs. Works that way for modern computer controlled vehicles of course, but ours are not that smart!

The fact that you don't get anything at the sending units is concerning. Initially it sounds like a bad gauge, but since you just installed new wires it would lead me to look there first.
Are the new harnesses rated for your year Bronco specifically? I wonder if there were some wire orientation changes at the firewall connectors over the years? Ford used the same connector design from '66 to '70, but they may very well have changed the "pinout" details during that time for all I know.

I'm assuming it's a '70 or earlier, only because I think those are the only years DC covers with their replacement harnesses.
If so, you should disconnect the firewall connectors and check the alternate connections on the firewall side. Since you know the engine side is not getting a signal from the IVR to the sending units, you need to know if it's even getting to the connector in order to track down the problem's source.

Good luck.

Paul

 

[bigdog137]

Hmm, odd one for sure. But I bet someone here will know intuitively what's going on.
A hot IVR is not right, as you suspected. Seems like a defective unit, but are they all acting the same as the original one you pulled out? Or was the original long gone already?
The gauges pegging upon initial turn of the key is wrong for our rigs. Works that way for modern computer controlled vehicles of course, but ours are not that smart!

The fact that you don't get anything at the sending units is concerning. Initially it sounds like a bad gauge, but since you just installed new wires it would lead me to look there first.
Are the new harnesses rated for your year Bronco specifically? I wonder if there were some wire orientation changes at the firewall connectors over the years? Ford used the same connector design from '66 to '70, but they may very well have changed the "pinout" details during that time for all I know.

I'm assuming it's a '70 or earlier, only because I think those are the only years DC covers with their replacement harnesses.
If so, you should disconnect the firewall connectors and check the alternate connections on the firewall side. Since you know the engine side is not getting a signal from the IVR to the sending units, you need to know if it's even getting to the connector in order to track down the problem's source.

Good luck.

Paul

I have used a 9v on the gauges and they full sweep. So they are off the hook. The DC main harness I bought was specifically made for 72 to 72. Now this is weird, the engine harness, the one that comes out behind the carb,, it has 3 wires. 1 oil, 1 water, and coil. I only get a reading coming out of the coil. nothing for the senders. so, power out of the IVR, nothing out of the sending unit connectors. This cant be that hard. lol. hey thanks again, at least i dont feel crazy now. maybe it is something simple.

 

[DirtDonk]

Check each point along the line. Easy to verify that power is coming out of the IVR first of all.
Then move to the gauges and see if power is going to, then out of the gauges.
Did you replace the gauges, or the gauge wiring as well?

For the IVR's, are they the standard electro-mechanical types, or the modern integrated-circuit type? Are you waiting until they are fully bolted down and the cluster is grounded to the dash before connecting them to the battery?

Paul

 

[bigdog137]

Check each point along the line. Easy to verify that power is coming out of the IVR first of all.
Then move to the gauges and see if power is going to, then out of the gauges.
Did you replace the gauges, or the gauge wiring as well?

For the IVR's, are they the standard electro-mechanical types, or the modern integrated-circuit type? Are you waiting until they are fully bolted down and the cluster is grounded to the dash before connecting them to the battery?

Paul

yes..other than the little heater connector it is all new. gauges, are all stock and original. the main wiring harness has the IVR hookups and gauge wiring and it is new. I am dreading it but if it isn't resolved I am pulling the dash and starting over. I did it all with the dash installed because I have a hole where the radio was and it made it easier, or so it seems.

 

[bigdog137]

Check each point along the line. Easy to verify that power is coming out of the IVR first of all.
Then move to the gauges and see if power is going to, then out of the gauges.
Did you replace the gauges, or the gauge wiring as well?

For the IVR's, are they the standard electro-mechanical types, or the modern integrated-circuit type? Are you waiting until they are fully bolted down and the cluster is grounded to the dash before connecting them to the battery?

Paul

Hey, I wanted to thank you. I went back through and just tried checking the blk/wht wire off the IVR and found that where it splits off from the IVR it looks like it had pulled apart. So i went back to the wires i had saved and tried the old connector and it appears to be working. One last question though, my old connector off the IVR was an individual wire that joined the three gauges. My new wire loom is a blk/white wire that comes out of the main harness. What is the difference?

 

[DirtDonk]

Perhaps they thought it was a better design than the original Ford, but more likely than not their supplier doesn’t have the equipment to make the fancy sealed splices like Fords supplier did back in the day.
So they simply crimped three wires together instead of daisy-chaining them.

 

[bigdog137]

Perhaps they thought it was a better design than the original Ford, but more likely than not their supplier doesn’t have the equipment to make the fancy sealed splices like Fords supplier did back in the day.
So they simply crimped three wires together instead of daisy-chaining them.

yes, my original is the ivr spade, the 3 press on for gas temp and oil. So it can be removed. The Dennis carpenter comes out of the main harness, 1 for temp and oil, then a separate for fuel., but they go into the loom. At this point i dont know where they come out. So i tried to retrace where the blk/white goes into the main harness and i see nothing. maybe it is for a different year. Seems odd. I placed the old one back on and it seems to work. Not sure if i did anything else right, but I am glad i posted this and you responded, and i am glad i didn't throw away the originals.. Should be back on the road tomorrow.

 

[DirtDonk]

Yes that is the definite rule of thumb when doing new wire. Never throw anything away!

If you get the chance can you take a picture or three of the harness in the area in question?
As far as I know the factory did not change the design of the gauge harness on the back of the cluster.