> The yellow with pink wire eventually goes from the relay to a black box
> called "sequential seatbelt control" (or something) the red and white wire
> goes from the ignition switch to this box also.
> BTW, this is a '74, was this when there was some law
> requiring that the seatbelt be used for the car to start? (this "feature"
> has been disabled and could be the root of my problem)
Ah, yes, the 1974 "broken ignition ciruit" requirement. By law, all ignition
circuits were required to be extra flakey in 1974, and when the ghost of
Mr. Lucas saw that, he just jumped up and down with fiendish glee.
> Also, why have this relay anyway? Isn't the solenoid a relay whose purpose
> is to limit the amount of current that has to go through the ignition switch?
> Does the solenoid require so much current it need a relay?
In a normal, sane ignition circuit, the ignition switch powers a small relay
built into the solenoid which routes the 12V line through the solenoid and
causes it to engage, which meshes the starter spur gear with the flywheel and
at the same tume routes the 12V through the starter windings. Sometimes there's
an interlock so that two low-current studs have to be energized in the right
order to make quick theft a bit slower. In an insane, abnormal 1974 ignition
circuit, there's this funky failure-prone relay that the ignition switch wire
goes through first that checks if you have your seatbelt on, have made the
appropriate sacrifices to the Prince of Darkness, and the moon is in the right
phase, and only activates the starter if all the above are "true", for some
values of "true". When this relay went flakey on my '74 Mustang, I got a 2'
piece of wire with alligator clips on each end (from my friend Doyle's lab)
and Doyle showed me how to fool the system: clip one lead to +12V, then poke
the relay lugs until you find the one that starts the car. The ignition must
be switched on for this to work. Failing that, you can use a big heavy wrench
to short across the solenoid switch lugs (the ones with the big thick cables).
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John R. Lupien
lupienj@hpwarq.hp.com
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