Having problems with my class C motorhome. It's a 1988 Ford cutaway chassis with 7.5L fuel injection. Bought it a few weeks ago for a good price, now I know why. Shortly after I got it I noticed first it wouldn't start without jumping the solenoid. Replaced the solenoid(s), it has 3 with a 2 battery setup. Still nothing. And now with the key off and out, any time you put a load on the battery, ie. stepping on brake, opening door and roof lamp comes on, 4 way flashers, the solenoids and relays start clicking and buzzing. Just for a few seconds for roof lamp and brakes but put the headlights on and they buzz and click constantly. It does not do this with the key in the on position. The starter solenoid is ok because I've attached a lead from the positive terminal of the battery and touched the s- terminal of the solenoid and it starts. Already replaced the ignition switch. Tried one from napa who said one size fits all, also tried one from the ford dealer with the same results. With the key in the start position I measured the voltage at the s-terminal of the solenoid and only got 7, guess that's why it won't fire. Battery load tested good, starter tested good, alternator is new before I bought it. All battery and solenoid leads wire brushed, sanded, and cleaned. When it starts I get way too much voltage at the battery 17-18 volts, battery starts bubling and spitting acid. Replaced external voltage regulator but same problem. With old regulator I disconnected the neg battery cable while running and the moter surged up and down for a few seconds then stalled. Also noticed temp gauge goes to maxiumum in a couple minutes after it's running even though engine is cold. Don't know where to go from here. Very baffled, any help would be greatly appreciated.

 

Get the regulator problem fixed first. The field terminal output controls the alternator output voltage. The A terminal is the reference point for the regulator. Check the wires. Be sure that you see battery voltage at the A terminal on the regulator. Do you have a ammeter or a idiot light?

 

I agree with Mike about the "A" terminal on the regulator. And I am also thinking your problem is in the area of #3 in the above diagram.

Your truck may not look exactly like the above, but it should have a point like #3 where all the 12v power is taken from the battery and distributed thoughout the truck. And also the "A" terminal is usually connected here too.

Different year trucks vary in how they tap off for the battery power, and you may find one large lead(but smaller than the battery lead) connected to point #3 and then leading out to a splice under the harness tape. You will also find many fusible links in this area. Some feed the EFI, some feed the fuel pump relays, some will be the main feed for the fuse box. If there is any corrosion in the splices under the harness tape, or possibly one of the fusible links has a marginal connection, then it could cause your low voltage problem.

By the way, that is probably why the relays are buzzing. The relays themselves take very little voltage to operate. But the loads they control usually do take a lot of current. So as soon as they kick in, the voltage drops and they kick out. The the voltage rises and they kick in, then the voltage drops and they kick out again.

 

Mike, Unplugged and tested the regulator A terminal. Got 12.4 volts with key off and 12.2 volts with key on, didn't test it while vehichle running, should I ? The A terminal also has a 2nd wire with a condenser attached.
Franklin at point #3 of your diagram there is a main battery lead of course, a large black lead from the alternator, a small yellow wire, and a black wire with an orange stripe. The yellow wire looks like it feeds into one of the relays (green) (attached to the inner fender well) and the black/orange looks like it feeds the brown relay right next to the green relay. The relays are in the same plastic housing. I'm still baffled as to why voltage feeds back though the solenoids (approx. 6 volts) and relays when a load is put on the battery with key off.
Guys thanks for your help on this, I really appreciate it. I hate electrical problems. All the other stuff I can do but this sucks.

paul

 

Paul, check the voltage at the field terminal while running. If it is just under your high battery voltage, the regulator is bad. On a working system the field voltage will vary depending on how much of a load the alternator has. If the field to alternator fld wire is pulled off, the alt will not charge. Also check the A term voltage while running. Usually it takes a fairly high rpm to see the high battery voltage you are getting if the field has full battery voltage.

 

Mike, Backprobed the F terminal while the engine was running and got 16.8v. Also put the meter across the main battery terminals while running and got 18.7v. Quick shut it off then and could here the battery bubling inside. This is off a new voltage regulator. I did not replace the condenser but I don't think that's it. Could the alternator be bad? Thanks again for your help.

paul

 

There alternator is ok. The regulator is telling it to put out max output. Be sure the regulator case has a good ground. Double check the wires and get another regulator. I made a test rig with a motor to spin the alternator. I clip lead a regulator up to the alternator and haven't damaged a regulator yet. I once put 12 volts on the field with the alternator turning at 5000 rpm and got about 70 volts out of it.

 

Mike, I figured it out (with your help). Ran a volt meter across main output of alternator and battery ground & got 12.6 volts with vehicle off. Ran to chassis ground and got only 11.2 volts...not enough ground. Rigged an 12 ga wire from Neg battery terminal to radiator support and all is fixed. When I got the beast I cut the metal trans lines to the radiator to bypass radiator trans cooler. Used rubber hose (not a good conductor, duh!!!). Guess those lines were a better part of the chassis ground. Thanks again, paul

 

Hmmmmn......I don't think the lines were the ground. I once saw the throttle cable act as a ground when the main ground connection was faulty. It wouldn't hurt to add a couple more ground wires. At least you are making progress.

 

Mike, I added a 4ga line from the block ground (which is hooked to neg bat terminal) to the frame. I also ran 2 more grounds with 12ga line. 1) to voltage regulator and 2) into the cab under the dash. Everything works well now. Got my fingers crossed.
thanks again.