Check the Wiring! By Juan C. Grube How manytimes have you told a cus- tomer or the new kid | er 4 , i working for you or —=s= 4 even yourself: “check the wiring”? P This means many different things to different people. Some “check the wir- ing” by just looking at it, some think if they pull on it and it stays connected that’s good enough. The only correct way to “check the wiring” is to perform a voltage drop test under load! This is easy and only takes minutes. But how do you check for voltage drop under load when a harness connector plug is disconnected or when an alternator is not working? When a connector plug is discon- nected and voltage is checked you may get an erroneous reading. That’s be- cause when a circuit is “open” the volt- age will always be the same through- out the circuit regardless of any resis- tance (bad connection) even if there is only one strand of wire left. It’s obvi- ous that you can’t make a voltage drop test on an alternator output wire when the alternator won’t work. So what do you do? Replace the alternator even though it may not be the problem? An example of checking and find- ing normal voltage with the plug discon- nected and not finding the problem would be any alternator with a bad “SENSE” wire. Even though the op- erating load on the sense circuit may only be milliamps, a bad sense wire may still show correct voltage with the plug disconnected. Granted what I’m talking about isn’t an everyday prob- lem, but it very probably could be the problem when the car is on its third alternator and the complaint is over- charging. Another example would be a Ford TAR alternator that is NOT working. This alternator has two wires that are subject to voltage drop problems. The regulator “A” wire is both the “SENSE” point and the source of field current. A small voltage drop in this wire affects the alternator output volt- age while a larger voltage drop reduces total amperage output. A voltage drop DELCO 105) 40 OH) HEGIETOH TO LOAD TEST “SENSE* CIRCUITS WK ta eS — | Syd [E JUNE/JULY, 2000 in the alternator battery wire needs no explanation, if bad enough the re- sult can be fire. How do you make a voltage drop test on an alternator that doesn’t work correctly? The answer is the same in both examples. You provide the load so current flows and an accurate volt- age reading can be made. How? Let me suggest that you make up ahead of time the following “load” test leads. For low current circuits use a 40 ST AMDARD IN-LINE “sh | | HANDHELD ‘OLTMETEA ALTERNATOR ROTOR 7S, FIELD COMLOAD ff os, TESTS. FIELD CIRCUIT | | 1 | ‘ ~_/ } —>_ = a FUSE HOLDER WITH 2 AMP PLSE WEHIGLE HARRESS CONNECTOR PLUG tg a STANDARD IA-LIBE HANDHELD VOLTMETER —— oF STATOR PHASE Loan | ——— | TESTS ALTEARATOA | —< -. | OUTPUT CIRCLNT e, = a , “=p ? HANDHELD VWOLTMETER FUSE HOLGER WITH 10 AMP FUSE VEHHILE HARNESS CONNECTOR PLUG |RSS SoMNECTED) AL TEAMATOR (84 OLTPLT WARE (WS CaAKECTED) Page 1 of 2