1970 mustang wiring?????

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  #1  
Old 10-23-04, 04:31 AM
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1970 mustang wiring?????

Howdie, My neice has a 70 Mustang with a 351M, automatic, power assisted steering. She just got this engine installed in her car, and she recruited me to help her get it wired and running. Why I dont know, guess she luvs me? Anyway, when checking, with my trusty ol test lite, the three prong wiring harness for the coil hot wire, temp gauge, and oil sending units, I discovered this-- #1- Coil wire was correct, 12v w/key on, #2- oil pressure sending unit wire and the temp gauge wire, with key on test light was blinking, with key turned to start, both sending units were still blinking. Pulsating current, if ya would call it that. I have never ran across this before, does anyone know what or why this is happening? Thanks Bullfrog
 
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Old 10-23-04, 08:42 AM
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The wires run to the guages which....

have an "instrument voltage regulator" that is supposed to keep about 5 volts for all the guages. (It's been a while, I might be off on the voltage). Your test light is looking for 12 volts and can't get it from the regulator...it may also be trying to draw too much current from the regulator.

If you need to know which wire is which, then ground one of them at a time on the engine block (with the key on). The gauge that wire goes to should go all the way over. (both gauges should peg). Don't worry about shorting it to the engine block...that's part of the IVR's job!

If you see the guages do the same thing as your test light, I would replace the IVR. I think it's somewhere behind the dashboard, you'll actually have to pull the instrument cluster out to get to it.
 
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Old 10-23-04, 01:20 PM
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Desy2820 is correct about the voltage regulator. It is normal for it to pulse when you hook a test lite to the sender wires. In fact that was one of the tests in diagnosing a guage problem.

Bullfrog66,

Did some one change it to a 351M ? They came with 351C or a 351W. 351M came out in '74.
 
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Old 10-27-04, 10:53 AM
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Howdie, Yes it is a 351W, I hit the wrong key, thanks for pointing that out. Thanks for the info also. Bullfrog
 
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Old 11-02-04, 04:22 PM
blsmith
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Question 351m

I know the Cleveland and the Windsor, but don't remember what the M is for?
 
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Old 11-02-04, 04:44 PM
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It is for modified
 
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Old 11-02-04, 05:23 PM
blsmith
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Thanks

I am now thinking that my 76' Country Squire had a 400M. Great wagon,terrible engine, the 460 got better gas milage. 9 MPG HWY, when well tuned. If I towed my boat it dropped to 6 MPG.
 
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