I have a 56 ford with a Y Block and a 700R4 transmission with a locking torque converter. The converter box has one unfused wire going to it from the ignition switch, and three wires (red, white and black) going to the transmission. My ignition switch failed, generally they fail from too much current, so I am installing multiple relays and fuses. What amp fuse is suggested for the power wire going to the torque locking converter box? The 700R4 installer is no longer in business. Fred
https://www.jalopyjournal.com/forum/threads/700r4-lockup-question.424985/ Im same.. i use relays for a lot the high current circuits to take the load off the switches. Some relays have their own fuses so make it simpler on the fuse box requirements.
Fuse size is determined by the wire size its protecting. Wire size is determined by the current it's meant to carry, and possibly how big voltage drop is acceptable.
Various sources (Painless wiring etc) cite a 20A fuse and 14ga wiring for the high current side of the relay, 2A and 18ga for the low current side up to the vacuum switch and dashboard control.
Thanks all. My setup does not have a vacuum switch. PhilA currently I only see the 4 wires with one coming from the ignition switch. Could it have been set up to run 20 Amps through the ignition switch? What do you think the other three wires red, black, white coming from the lockup box do? Would it lockup more than 4th? Fred
This will work. And by the way there is no high amp load in the transmission control circuit. Only an oil solenoid that applies to hydraulicly engage lockup.. but you must have a two pole 4th gear pressure switch. ALERT! Some of you guys are clicking on the link but not giving it time to go to the specific wiring diagram. If you tap the results of the link too quick it just goes to the first picture of the gallery. So when you tap the link just wait a few seconds. https://49fordcoupe.smugmug.com/The-700R4-Chapter-2/i-pmqMg59
The lockup clutch solenoid does not draw a lot of current. 2 amps max? from memory. All the solenoid does is redirect the ATF to hydraulically engage the clutch. Most kits recommend running it through a 20 amp fused supply. Do you know what brand of kit was used?
If you measure the resistance of the solenoid (ohms) with a simple multimeter you can get how many amps the circuit will draw For example if you read 6 ohms across the solenoid and your car is 12 volts then the circuit would draw around 2 amps. This works for any inductive load, headlights, fans etc.
Headlights are resistive, not inductive. In the specific case of lightbulbs the resistance of the filament changes drastically with temperature meaning the calculated current based on the cold resistance will be way higher than the actual current through the lamp when it's lit. Electrical motors such as fans will also give an incorrect calculated value, the calculation may be right for the motor when it's locked up, the current goes down quite a lot when it's running at normal rpm. The calculation will be good for the solenoid, but some other things, not so much.
I used a #14 wire and a 15a. fuse, but doubt it needed 15a. protection. My 700R4 wiring starts as a single wire to a toggle switch, and from the switch it goes to a hydraulic pressure switch that controls lockup. From the pressure switch the wiring goes to the 4 pin plug connected to the correct terminal for 4th gear converter lockup. Then a wire to ground off the 4 pin plug. Which two pins you use depends on how the trans is wired and I was warned to not count on it being correct if the trans had been rebuilt. Seems trans shops occasionally get the wires swapped, so no telling which two of the 4 pins are connected to 4th OD converter solenoid. Easy to trace them out with the pan off the ******.
I'll add to this.... To calculate lamp loads you have to use the lamp watt rating. Virtually all automotive incandescent bulbs are rated in watts, divide the watts by the volts to get the current draw when 'on'. A 60 watt headlight will draw 5 amps when on. And as G-son says, the filament resistance can change drastically between 'off' and 'on'. The typical 1157 brake filament measures roughly 2 ohms 'cold' but increases to over 6 ohms when lit. There is a current inrush in virtually any circuit when first energized however, so this does need to be addressed in some cases. Generally with lighting loads fusing the circuit at 125% of the calculated load will be adequate. Inductive loads are much trickier. Most automotive circuits are inductive, lights and some gauges are generally the only purely resistive loads you'll find. These can be further divided into two categories; ones that do mechanical 'work' and those that don't. Ignition coils are the prime example of the latter, although I'll note here most better modern electronic ignition controls have current-limiting circuitry or dwell control to prevent coil overheating at slower speeds (allowing you to eliminate the ballast resistor). Doing a simple ohm reading across the coil primary will be reasonably accurate to get you in the ballpark. Any inductive device that causes mechanical movement will need enough power (in watts or HP) to perform its work. Simple devices like solenoids and relays can be read with an ohmmeter well enough to get you close. Don't try this with motors; do the research to find the required circuit size. There are two things that can have an outsized negative impact on these circuits; one is increased load. If the load is higher than the design parameter, the device will draw more current in an attempt to perform the work. Whether it's a sticking solenoid valve or a bind in a motor-driven ***embly, this will cause current to go up, along with heat generated that will shorten the life of the device. The second thing is voltage drop from undersized wires. Again, if voltage is low the device will draw more current attempting to produce the same amount of 'power'. This can turn into a vicious cycle as the increased heat will raise the internal resistance of the device, further reducing voltage and increasing current, etc etc...
I have a 5 A fuse in mine and it’s fine. Mine is a TCI lockup kit with vacuum switch. As others say, it’s just a small solenoid that causes the lock up. John
Thanks All My 700R4 was installed by Bendtsen Transmission Service and at the time he seemed to say the locking converter kit was his own design. Almostdone, interesting I emailed TCI and they replied 10A fuse. Did TCI tell you 5A or just did not say anything? Fred
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