Oil Pressure Switch Wiring Connection?

[JL100]

I have an Oil warning light on my console of the '67 F100. My temp gauge hasn't worked since I bought the truck 3 weeks ago, and I am just now getting around to trying to fix it. There are three wires under the hood with "connectors" on the end of them, one of the wires hooks into the end of the "Oil Pressure Switch" which is screwed into the side of the engine (bottom drives side of engine.) I cannot figure where these three wires hook onto. One of them hooks onto the end of the Oil Pressure Switch, and I have tried a mixture of all three in different connections, none of which seems to work. When I hook up two of them, there is no response on the temp gauge inside the truck. When I hook up the other one, the temp gauge goes all the way to HOT and runs there the entire time. I know there has to be a fix for this, and I was wondering if anyone had any insight. I have looked on some of the wiring diagrams here on the site, and found very little to completely explain what I am looking at. Thanks for any help, trying to get this fixed today.

[Thunderfoot]

The one White/red striped wire is the only wire for the Oil Pressure gauge.
The one Red/white striped wire is the only wire for the Temp gauge.
The one Red/green striped wire goes to the (+) side of the coil, this is the ignition wire to make the engine run.

The sending units work by grounding themselves to the engine which makes the gauge move and only use one wire each,,, so to test the gauge, if you take the wire for the Oil Pressure or the the wire for the Temp and ground it to the block, the gauge should go all the way to max range. If the gauge doesn't move then either the gauge is bad or the wire has a brake in it.
If the gauge moved doing this test grounding the wire, then the sending unit is bad if you are not getting any movement out of it with the wire connected to it.

[JL100]

You are a great man for his help. I just put in a new sending unit yesterday, so I should start to find out what exactly isn't working and what is. Thanks again, I'll let you know my results.

[JL100]

Ok so the three wires I was speaking of on my truck are as follows.

Red/White Stripe - connected to Oil pressure switch sending unit

Yellow/Red Stripe - hooked onto nothing currently

Black - grounded on block

Any thoughts on if this is right, or what the Yellow/Red Stripe goes to? Thanks!

[Thunderfoot]

Ok so the three wires I was speaking of on my truck are as follows.

Red/White Stripe - connected to Oil pressure switch sending unit This one needs to go to the Water Temp sending unit

Yellow/Red Stripe - hooked onto nothing currently This one should be the Oil Pressure sending unit wire, the white has probably yellowed over 40yrs

Black - grounded on block I don't know what this black wire is there shouldn't be any black wires in the harness going to the engine compartment, what wire is connected to the the (+) side of the coil? I take it the truck is running so this one might be an add-on from the PO... Another thing to do to check these wire is to use a test light and check them for power with the key on, if they are going to the gauges and the gauges are working there should be a dim pulsing light on the test light. The power to the on the wires to the sending units is around 6V if you have a voltage meter to check them with.

Any thoughts on if this is right, or what the Yellow/Red Stripe goes to? Thanks!

[JL100]

Ok, so thanks for the great description. Here's an update on the progress.

The black wire is connected to the Ignition Coil I believe. When I disconnected it from the coil and tried to start the truck, it would not start, period. I connected it back and it started quickly and normally.

With the "Yellow/red stripe" wire connected to the Oil Pressure switch now, he temp needle stays all the way Cold. I have not driven the truck yet today though, so that may change.

This makes me feel stupid, but I'm having trouble identifying the "Water Temp sending unit" any ideas on where to point me? With not knowing where to find it, the Red/White Stripe wire is just hanging loose at the moment. Could that cause the temp gauge to malfunction?

[Thunderfoot]

Sounds like the PO must have replaced the Red/green striped wire with some Black wire at some time...

See here for location of the temp sending unit. http://www.fordification.com/forum/view ... 27#p454827

[JL100]

Thunderfoot you are a life saver. AMAZING help, I would have never found that. It's harder on my engine because the PO painted the entire engine ford blue, including painting over these switches. So what would normally stand out being silver or shiny is just all blue. I hooked up the Red/White Stripe to the water temp sending unit, now we will see what results I get. Thanks again!

[Thunderfoot]

Glad you found it... I see from your sig you have a I-6 so that pic probably didn't help much...

[JL100]

Glad you found it... I see from your sig you have a I-6 so that pic probably didn't help much...

HAHA, well it got me looking in the right direction. It was at night, and I haven't had a chance to go back out to the truck and look at it so let's hope I did find it. Either way sir, feel confident that you will hear from me. It seems like you are my #1 resource at this time.

[JL100]

Ok, so I finally got around to taking the truck out for a good length drive. Great news, the Temp Gauge works!!

I may be running a little hot. Either way I am going to replace the Water Temp Switch and the Thermostat on the truck to have full peace of mind in the function of the system. Thanks SO much for all the help.