scbill Posted February 16, 2021 Share Posted February 16, 2021 What is the voltage supposed to be @ the top connector blu/grn from ign switch, should start as 12v thru a resistor wire. Does the resistor wire drop voltage, or amps? I am a volts/amps/elect challenged person. Thanks Bill Link to comment Share on other sites More sharing options...
Gary Lewis Posted February 16, 2021 Share Posted February 16, 2021 I can't really read that schematic due to the size, and if I make it larger it get blurry. Where did you get it? What is it for? If it is for a Duraspark ignition can we use the schematic from Ford? Documentation/Electrical/EVTM/1985 EVTM. Here's the schematic for Duraspark. But the answer to the question about resistance is that in this case it drops voltage and current. The equation is E (voltage) = I (current) x R (resistance). BUT, if you are trying to measure the voltage after a resistor you must have the load on pulling current or the voltage will not drop. So, tell us more about what you are doing? Link to comment Share on other sites More sharing options...
scbill Posted February 16, 2021 Author Share Posted February 16, 2021 I can't really read that schematic due to the size, and if I make it larger it get blurry. Where did you get it? What is it for? If it is for a Duraspark ignition can we use the schematic from Ford? Documentation/Electrical/EVTM/1985 EVTM. Here's the schematic for Duraspark. But the answer to the question about resistance is that in this case it drops voltage and current. The equation is E (voltage) = I (current) x R (resistance). BUT, if you are trying to measure the voltage after a resistor you must have the load on pulling current or the voltage will not drop. So, tell us more about what you are doing? Gary, It's the blk/grn wire from the ignition...changes to blu/grn when it gets to the big plug on back of the main plug on the instrument cluster. I assume it's the power for the gauges. Page is from Haynes Ford truck/bronco manual. I'm trying to find the voltage input for the cluster. Link to comment Share on other sites More sharing options...
Gary Lewis Posted February 16, 2021 Share Posted February 16, 2021 Gary, It's the blk/grn wire from the ignition...changes to blu/grn when it gets to the big plug on back of the main plug on the instrument cluster. I assume it's the power for the gauges. Page is from Haynes Ford truck/bronco manual. I'm trying to find the voltage input for the cluster. Ok, I think I understand. Here's the info from the '85 EVTM. We'll start with the ignition switch. Note the big blue triangle with an "N" right in the middle of the page. It says "To Instrument Cluster Page 98, 106". And here's page 98. Does that help? Do you need to know what pin that wire is on? Link to comment Share on other sites More sharing options...
scbill Posted February 16, 2021 Author Share Posted February 16, 2021 Ok, I think I understand. Here's the info from the '85 EVTM. We'll start with the ignition switch. Note the big blue triangle with an "N" right in the middle of the page. It says "To Instrument Cluster Page 98, 106". And here's page 98. Does that help? Do you need to know what pin that wire is on? Voltage at C208A at the cluster plug is what I was needing, I'm trying to chase down gauges not working. going to save these diagrams tho..may try the offboard voltage setup that you posted. Thanks Gary. Link to comment Share on other sites More sharing options...
Gary Lewis Posted February 16, 2021 Share Posted February 16, 2021 Voltage at C208A at the cluster plug is what I was needing, I'm trying to chase down gauges not working. going to save these diagrams tho..may try the offboard voltage setup that you posted. Thanks Gary. You do know that those diagrams are on the site? Documentation/Electrical/EVTM/1985 EVTM. Every circuit on the truck is shown in there. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted February 17, 2021 Share Posted February 17, 2021 You do know that those diagrams are on the site? Documentation/Electrical/EVTM/1985 EVTM. Every circuit on the truck is shown in there. A lot of times it's easier to have a piece of paper in hand. Greasy fingers and sun glare make working with a mobile device 'challenging' at best, and impossible often enough. But I'll agree Chilton and Haynes schematics are next to useless when you have an EVTM in hand. Link to comment Share on other sites More sharing options...
PetesPonies Posted February 17, 2021 Share Posted February 17, 2021 Resistors in series create voltage drops. The drop is proportional to the resistors resistance in reference to the entire resistance of the circuit. If you had 12V and a 10ohm resistor and the load was also 10 ohms, you would find 6V at the resistor and 6V at the load. Most of the time, gauges work around 5-6V. They are feed through an IVR, Instrument Voltage Regulator. Link to comment Share on other sites More sharing options...
scbill Posted February 17, 2021 Author Share Posted February 17, 2021 Resistors in series create voltage drops. The drop is proportional to the resistors resistance in reference to the entire resistance of the circuit. If you had 12V and a 10ohm resistor and the load was also 10 ohms, you would find 6V at the resistor and 6V at the load. Most of the time, gauges work around 5-6V. They are feed through an IVR, Instrument Voltage Regulator. Methinks it's the wire that is the culprit in this series of trucks, apparently most all of them has the same problem(s). Thanks for all the info..Bill Link to comment Share on other sites More sharing options...
Gary Lewis Posted February 17, 2021 Share Posted February 17, 2021 Methinks it's the wire that is the culprit in this series of trucks, apparently most all of them has the same problem(s). Thanks for all the info..Bill What is the problem? I haven't heard of a lot of wiring problems. Yes, the ICVR is a problem, but not usually the wiring. Link to comment Share on other sites More sharing options...
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