I've got a nice low mileage (67,000) 74 f100. I doesn't see any inclement weather any longer, but, the other day, i got caught in the rain. I already had the heat, & headlights on, as it was an early morning swap meet. i noticed in the past that as i sit at a light, the heater seems to "power up" then back down again. i put an N.O.S. blower motor, & heater core in a few weeks ago, i was hoping that the new blower motor would have solved this, but it didn't. I also noticed that the brake lights do a similar thing when i back into the garage. Any thoughts?

 

Would it be the old breaker points style voltage regulator doing its thing? Or maybe a not-so-good reman alternator?

My '68 Cougar used to do something that, and I could hear it in the radio too. But I'd changed the voltage regulator in the Cougar, and I would think that the McParts store voltage regulator from 1996 would've been solid state, but maybe not. I definitely had the el-cheapo McParts reman alternator in that car though...

 

Well by definition that's a voltage regulation problem. That needs fixed. Did Ford still use a separate voltage regulator at that time, I'm thinking yes, probably even mechanical as mentioned. These older trucks always have ground point and cable corrosion issues, high resistance connections. If they have restored or upgraded the common problem is thick layers of paint.

The voltage regulator itself needs a solid electrical reference to ground, if the regulator body is lifted relative to ground it can get wonky. If it is mechanical regulator type the internal points too need cleaning now and then with a file. Let us know what you find. If you measure the charging voltage at the battery posts while heater and blower on at a high idle that might be interesting.

I always recommend fresh ground and battery cables if they are original to the truck, and grinding clean bright shiny tight connections at the engine block, frame, and firewall too. This makes a tremendous difference in engine starting performance, charging, lights, ignition etc.

 

Point type alternator regulator used thru 1981, replaced by an electronic regulator in 1982. Ford updated the part number in 1990.

FOPZ-10316-A (replaced C3SZ-10316-A & B; D4TZ-10316-A; E2PZ-10316-A) .. Alternator Regulator-Electronic (Motorcraft GR-540-B) / Available from Ford

1963 Thunderbird first FoMoCo vehicle to have an alternator as standard equipment, everything else got it in 1965.

 

David.....

 

Thanks for all the responses. When i bought the truck two years ago, the starter went out. Seeing as it had sat for two years prior to that, i replaced the battery, starter, solenoid, cables, voltage regulator, & a ground strap from the block to the firewall, as well as a ground strap from the firewall to the hood. I did replace the core support because while the truck sat out in the sub-zero temps, froze the battery, then thawed, & ate up some of the core support. I blasted, primed, & painted the support, so maybe the paint buildup is the issue as Tedster9 mentioned. Be nice if it was a nice simple fix like that

 

First link - as always be careful - lots of potential energy in an automotive start battery

http://www.aa1car.com/library/battery_safety.htm

Now that the lecture is out of the way (you did read it right? Nod your head "yes")

Use your voltmeter to run the tests described in the following links. They should be helpful. If paint is contributing to the issue the voltage drop testing will expose the offender pretty quick.

http://www.aa1car.com/library/charging_checks.htm

http://www.aa1car.com/library/voltage_drop_testing.htm