electrical rewire

1

1hc72

Member
im rewiring the starting aspect of my truck. got a few of the wires figured out( i think) if i can get some confirmation that would be great, ( i do have the wiring manual forthe 72 up full size but my truck is a 71 so not sure if the schematcis are going to be correct)

Yellow wire is the the styart wire from the ign switch( was orrignaly yellow so i kept he same color) the green one is from the positive side of the coil

postive main wire off starter cylanoid (red is going to battery the black and blue is stil the original( i think that goes to cab for main power?)

came from the origina( i think ) alt, the black wire came from the plug on the side of the alt, the green termainal was taped up so im not sure were or what that was for(upgrading to a GM one wire alt at this time)

this was the orignal wires from the coil not sure what the wire did, and i am un able to trace it out.

thank you for your time.

1971 1210 camper special 345 v8 manual trans 2wd
 
There is little, if any difference in wiring between a '71 and '72. Your starter solenoid has three terminals. The large one is the battery connection. Your original wires that were connected there would have had large eyelet ring terminals, so it should be an easy process of elimination to know which wires go on that large stud. Now to the two smaller terminals. One should be labeled 'S' for START signal...yellow wire from IGN. The other should be labeled 'R' for RESISTOR bypass...green wire to coil (+).
That ugly, cloth jacketed wire that was also running to the coil (+) terminal is a resistor wire. It was originally 72 inches long from the factory. That length is what gave it a resistance value of 1.8 ohms when probed from end to end with a multi-meter. That resistance steps down the battery voltage slightly while the engine is running to protect the points and the coil from overheating and frying to a crisp. If that wire is damaged beyond use or the length has been shortened more than an inch or two, then it is no longer viable. It originates from the bulkhead connector at roughly the center of the firewall. So examine it carefully and determine whether or not it is still viable per my description. If not viable, then you will need to snip it within 6 inches of the bulkhead connector and discard it. Then you will need to buy a ceramic ballast resistor having a resistance value of 1.8 ohms and mount it to the firewall more or less inline with the passenger side wiring loom that runs down the engine to the coil. You'll then splice a 14 GA wire to the short chunk of that resistor wire where it comes out of the bulkhead connector and run it over to the nearest side of the ballast resistor you mounted to the firewall. Then you'll run a new chunk of the same wire from the opposite resistor terminal on down to the coil (+) terminal. The green wire I identified as the Resistor bypass wire provides full battery voltage to the coil only while starter cranking. Once the engine barks off and you release the key from START to ON, the resistive feed takes over until you switch the key to OFF. Now, if you're no longer running breaker points and have switched to some type of electronic ignition, you need to speak up about that, because that will change some things.
 
not sure if it was converted over or not, i can check under the dizzy cover tomorrow and get a few pics to aid in ID, will def tear thru the wiring section of the manual for making sure i didnt snip off more that i needed to,
 
ok i have an update but im confused. got the starter in, wired correctly but all it does is click, i jumped the I and the pos post on the starter(elminating all in cab or i oppsied wire) and it still jut clicks like battery is dead, i checked and it had 12.4 V. any ideas on were i can go from heare? thanks in advacnce
 
A number of possibilities here. Battery could have a bad cell. While displaying nearly a full charge at rest, a battery with a bad cell will not have enough cranking amps to engage a starter motor under the load of an engine. You can have it load tested at a parts store. Your ground connection between the battery and the engine block is loose, corroded or otherwise faulty in some way. Could be a bad cable. Same with the large positive cable from the battery to the starter solenoid. Double check for quality connections on both cables at both ends of each. The starter motor itself is bad. It's easy to test a starter motor away from the engine. I know they are a pain to mount and dismount from the engine, but once out, all you need is a good battery and a set of jumper cables to "bench test" a starter. The engine is physically stuck or seized. Even the best starter in the world can't turn over a stuck engine.
 
ok will check that out starter is new, altho i know that dont mean much anymore. will try to manulla roll the mootor over it shouldnt be stuck but will verify that later today
 
ok im lost. pulled starter, tested it off jumper pack, tested good, hooked to battery tested good, while starter was out barred engine over spins free hit compresstion stroke and i cant move it (tiny ratchet) so now were do i go? wiring ws routed correctly before i pulled it out(yes double checked the wiring diagram as well) any ideas?
 
Stupid question, but have to ask. Manual transmission...are you sure you have it out of gear? Get a bigger wrench on it and see if you can get two full revolutions by hand, but you shouldn't have to put hernia popping torque on it. You could have some stuck valves and/or bent pushrods or some other type of internal mechanical bind. What's the history on this motor?
 
i THINK it is in gear actauly, it ran when i got it, broke the throttle cable and the can of worms opened from there, wil have to pull it out of gear and see if that does it thank you :)
 
Hope so. That would explain it and be a cheap and easy fix. Definitely don't want it in gear while you're trying to start it for lots of reasons.
 
i feel like im an inch tall, truck was in gear spins over great just dont want fire(but i dont have fuel going to it either ) sprayed carb cleaner down it and it pops but dont idle
 
Great news! You'll have a hard time getting it to run on carb cleaner. Not recommended. Better would be to temporarily plumb it to a fresh fuel can if the onboard tank isn't an option. You can carefully pour some fuel into the bowl via the top vent opening. A full fuel bowl should run it for 15.or 20 seconds.
 
threw some gas down the carb spins over great no fire, had a helper check and i have no spark, connection at coil end is good and tighht with both the green wire and the resistor? on top of the coil, the connection on the starter could be tighter(will take care of that here in a few days soon as i can get a 9MM socket) im using an amazon `12v coil. wer to go from hgere i know i still need the 1.8 ohn thing( wil be ordering asoon as i can)
 
The doohicky on top of the coil is not a resistor or condensor. It's a RFI noise suppressor. It has nothing to do with your ignition system performance. It can be deleted if you wish. Post a pic of your coil so I can see what wires are hooked up where.
 
Ok. The reason why it won't stay running is that green wire from the solenoid is only energized while the starter motor is cranking. The ballast feed which you don't have yet is what keeps it running in the key ON position
 
ok so i have a stupid question. if i give coil 12v+ direct from batt will i fry everything even for 30-45 sec of run time?
 
No. You can run a temp jumper direct from the battery for limited diagnostic purposes. That's your kill switch too. Be sure not to leave it connected with the engine stopped.
 
You must log in or register to reply here.
Back
Top