Checking Jacobs Brake Wiring

6TS 3406E, Jacobs 340A, In a KW

Truck's acted like it was only firing on 2 out of the 3 jake heads on the trip home. Stage 1 is non-existant, and stage 3 feels like stage 2. Previous trucks experiences make me suspect that something is up on the #2 Jake head, holes 3 and 4. Resistance through the solenoids is a steady 10.3-10.5 ohms in all three solenoids. Press down on the solenoids all of them mechanically work, Solenoid #2 did give some resistance, but hit the Jake fine after a second.

So either something was gummed up (I hope), or I have got to check the wiring, does anybody have a schematic for the connector that goes into the spacer plate? I would have to think that this would be the easiest place to check both the internal wiring, and wiring to the ECM. Also, does a guy have to have someone rev the truck up and let off while I run the voltmeter (I think), or is it mechanic friendly and should show voltage whenever the dash switch is on (seems unlikely but people get lucky).

I want to finish checking out my wiring and probably run the rack (just bought truck at auction, hasn't had valve train adjusted in 5 years) before I get everything buttoned up. Hopefully I get lucky and something was just stuck, but I'd rather not have to pull my valve covers off twice. Thought I'd try to get some answers on here before the Cathouse opens tomorrow.