Just picked up a very nice '70 F250 Sport Custom Camper Special.
It has a 390 CID and the previous owner converted the auto trans to a 4-speed granny low. Overall I have to say the trans conversion is first class, including the column neutral switch bi-pass, as it looks like a factory job.
My problem is I can't get the proper voltage at the ignition switch. It's at 3.5 volts +/-. The truck is not running on it's own yet. I replaced the battery and installed an aftermarket HEI distributor, so I can run the engine just off the battery. They had a bunch of crazy dash wiring which I have removed but once that was done the wiring harness inside the dash looks pretty much factory original.
So other than normal aging the wiring is OK. But my problem is I can't get 12 volts on the primary power wire 37 (black-yellow) at the fuse box, or on 21 (yellow) at the ignition switch. 37 doesn't seem to connect directly to the Starter Motor Relay, either. I've looked over the harness and it doesn't look modified but I could be wrong.
Anybody shed light on this? I have a feeling I need to connect 37 (black-yellow) to the Starter Motor Relay, so maybe the 3.5 volt is just feedback through other circuits?
Nate
Wierd Voltage
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Mach428
- Blue Oval Fan
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Re: Wierd Voltage
Wow. I wish I had the wiring schematic in front of me but it's at home.
That said, you should be able to trace the lines in the wiring manual to see where the ignition switch gets its voltage and if there are any other devices that could affect voltage. Working from memory, I don't believe there are any. So starting at the battery side of the solenoid, follow the smaller wire to see where it goes and if you have voltage at the next junction. That's how I do it. Process of elimination will work every time.
That said, you should be able to trace the lines in the wiring manual to see where the ignition switch gets its voltage and if there are any other devices that could affect voltage. Working from memory, I don't believe there are any. So starting at the battery side of the solenoid, follow the smaller wire to see where it goes and if you have voltage at the next junction. That's how I do it. Process of elimination will work every time.
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68RGR
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Re: Wierd Voltage
Barring any odd ball changes made by the PO, the black-yellow wire SHOULD connect to the starter solenoid. At least, it does on my '68.
When you do locate and connect it, you might want to add a 40 amp (or so) fuse or circuit breaker inline. I make that suggestion because, once, when I was trying to get my parking brake to release properly, the vibration (apparently) caused the ignition switch to fall apart! The rear part (where the harness connects) managed to find a ground. And, wouldn't you know it? It was that black-yellow wire that got shorted to ground releasing the 40+ year-old smoke in the insulation! Fortunately, I had seen something similar years earlier and was Johnny-On-The-Spot to yank the cable off the battery post!
That one event could have burned up two trucks along with my garage.
It's hard to say where the 3.5 volts originates. One thought is the vibrator-type regulator for the gauges but it should produce 5 or 6 volts.
Could there be a kill switch somewhere? You know, an anti-theft type disconnect that's hidden?
One idea would be to locate the black-yellow under the hood, attach a 6 or 8 foot piece of wire to it, run that wire into the cab temporarily to check for continuity with the other end of the black-yellow wire at the switch. If that part is good, try touching the under hood end of the black-yellow to the solenoid terminal with the harness connected to the switch. If no large arcs or smoke result, then proceed to check it out further.
When you do locate and connect it, you might want to add a 40 amp (or so) fuse or circuit breaker inline. I make that suggestion because, once, when I was trying to get my parking brake to release properly, the vibration (apparently) caused the ignition switch to fall apart! The rear part (where the harness connects) managed to find a ground. And, wouldn't you know it? It was that black-yellow wire that got shorted to ground releasing the 40+ year-old smoke in the insulation! Fortunately, I had seen something similar years earlier and was Johnny-On-The-Spot to yank the cable off the battery post!
That one event could have burned up two trucks along with my garage.
It's hard to say where the 3.5 volts originates. One thought is the vibrator-type regulator for the gauges but it should produce 5 or 6 volts.
Could there be a kill switch somewhere? You know, an anti-theft type disconnect that's hidden?
One idea would be to locate the black-yellow under the hood, attach a 6 or 8 foot piece of wire to it, run that wire into the cab temporarily to check for continuity with the other end of the black-yellow wire at the switch. If that part is good, try touching the under hood end of the black-yellow to the solenoid terminal with the harness connected to the switch. If no large arcs or smoke result, then proceed to check it out further.
Bill
68 F100 Ranger
73 F100 Ranger XLT
Believe me, my young friend, there is nothing - absolutely nothing - half so much worth doing as simply messing about in garages. (Apologies to Kenneth Grahame.)
68 F100 Ranger
73 F100 Ranger XLT
Believe me, my young friend, there is nothing - absolutely nothing - half so much worth doing as simply messing about in garages. (Apologies to Kenneth Grahame.)