Nagging Electrical Problems

[B-Co Kid]

1987 B-Co, 351w, carb'd, borg warner 1356, without EEC.

Ive been have the same electrical problems for a while and i cant figure out why. When using the power window(s), power lock(s), tailgate window, there is a noticeable drop in voltage, the interior lights dim and the volts dop from 14 to around 11, and when i let go of the switch, the voltage returns. I recently did the 3g swap, that didnt help. i recently replaced ground wires, from battery to block, from block to frame, and from frame to chassis, still didnt help. I had the interstate battery tested, and it tested ok. I tried putting a homemade test light between the +battery post and the +battery wire, and it lit very dim, even when ALL of the fuses where pulled, the light was lit, but very very dim. When i opened the door(s) it lit bright. Not sure what else to check. I thought maybe the ground for the power windows/locks may be bad, but i dont know where to locate the ground wire location. HELP!

Update: Did another quick check with the homemade test light, and the light went out completely when i pull fuse position #8, which is the cargo light/dome light circuit. How do i find out which one is my problem?

 

[Rons beast]

Hey Kid,

You may not have any problems at all. It is normal for there to be a momentary voltage drop when you switch on those components. I have the 3g alt conversion, and get the same thing. They pull a fair amount of initial amps when activated and a voltage drop is expected. The alt. should recover quickly. In some instances when idling it may take a little longer. Check your idle speed. If it's under spec, you may want to raise it, and give the alternator a little more push.

As far as your test light checks. That is a check for a drain on the battery. You didn't say that you had a problem with your battery draining. The dim light could be from a channel memory in a radio, and or clock. When you opened the door and the light got bright, it indicates that that circuit is demanding voltage as needed. It's normal.

If you have a concern that you have that dim light, when all accesories are off, you can disconnect the radio, and clock, if you have one, and see if that does the trick. Problem is when you hook them back up you will get a dim light again, as they need a small amount of voltage to retain memory and power the clock.

Good Luck

 

[B-Co Kid]

Thanks for the reply ron, i guess I can live with the voltage drop when using power windows/locks; but I do have a problem with the battery draining whenever I use the radio/cd player for about 5-10 mins with the engine off. Seems like that's a significant drain in such a short period.

 

[Rons beast]

Hey Kid,

Are you running an Amp or Amps with the stereo? If so are they wired direct to the battery? They may be drawing power even when the radio is off.

If you do have one of the killer sound systems they will **** batteries. You may want to think about an Optima Battery. You could also isolate the power to the sound system, so when you want it off it's off

Good luck

 

[B-Co Kid]

No amp, no fog lights, no big speakers, no elec fan, just an aftermarket cd player. That's why I don't understand why it drains so fast.

 

[Rons beast]

Hey Kid,

Check the glove box light. I have found that it gets out of adjustment and can stay on even with the door closed.

If all you get is a dim light, and the battery still drains, it is likely that the battery has been discharged and hasen't had the charge time to recover...OR can't recover and a battery replacement is needed.

be sure the battery gets a good strong charge. No quick charge. A good trickle charge done overnight with a charger with overcharge safety is best.

Also if the battery is the type you can check the "water" get a battery specific gravity tester, and check each cell. If you can, check before and after a charge. 1230 to 1300 is good. Any cell with dark or "black" looking fluid is dead...the battery needs replaced.

Good Luck

 

[B-Co Kid]

I removed all accessory light bulbs and disconnected the wiring to them, ash tray, glove box. I will try charging the battery and see if that helps. I have the biggest baddest interstate battery, megaton plus, which I thought was a pretty good battery, but I will check out the optima. But if the dim light goes out when I pull circuit# 8, dome/map/cargo lights and warning buzzer, seem like my problem would be there, except I have disconnected each one of those accessories and still have the dim light. Will give charging the battery a shot..

 

[Rons beast]

Hey Kid,

A Dim light should not drain your battery, unless left for a couple weeks.

 

[Seabronc]

Just a few thoughts. Looking at what fuse 8 controls, there is no reason for a drain on that circuit if the interior lights and warning buzzer are not in use (lights off and buzzer is not going off). That indicates tat there is probably a low resistance short some place or there is a light on that you are not aware of, (like Ron mentioned before, hidden lights like the glove compartment). I don't happen to have an 87 EVTM but that would be like lights under the dash, glove compartment, dome light, cargo area lights. This kind of problem takes some systematic trouble shooting and a good wiring diagram so you can isolate one thing at a time from that circuit. A common problem is a high resistance short where a wire passes through or near a metal part of the truck. If it were a dead short it would blow the fuse. However, wire that has insulation rubbed off and is just barely making contact with a grounded part of the truck will not necessarily be a dead short.

The question is where do you get a, "GOOD, EASY TO FOLLOW", wiring diagram. The only source for those is the EVTM (Electrical and Vacuum Troubleshooting Manual) for the year of your vehicle. I would rate the EVTM as one of the most valuable tools for troubleshooting you could own. They are generally available on eBay, the Chilton and Haynes books have diagrams in them but you will have a headache trying to follow them. The EVTM only shows what is in a particular circuit so you don't get lost by crossing over into another circuit.

As far as the voltage drop when operating windows, is that with the engine running? And where are you doing the measurement?

I would check the ground connection that is under the dash and attached to a firewall support. That is one of the major grounding points in the truck. Also there should be a ground strap from back of the driver side intake manifold to the fire wall. It connects to the fire wall just about oposit from the under dash location. Check it and clean the contact points. If thye strap is corroded, replace it.

Good luck,

 

[B-Co Kid]

Thanks for the info seabronc. All accessory lights (glove box, ashtray, engine light, warning buzzer, and cargo lights have been disconnected). I had my battery tested @ the zone, and they said it had 50% charge, so I left it to charge for the day. That's probably why it drains quickly, however it's about a year old and its a interstate megatron plus, I figured it would have lasted longer. Anyway, as far as voltage drop, I'm looking at the meter on the instrument cluster, it drops from 14.5 v down to about 12 v when using power windows. Hopefully the recharged battery will correct my drain problem.

 

[Seabronc]

Thanks for the info seabronc. All accessory lights (glove box, ashtray, engine light, warning buzzer, and cargo lights have been disconnected). I had my battery tested @ the zone, and they said it had 50% charge, so I left it to charge for the day. That's probably why it drains quickly, however it's about a year old and its a interstate megatron plus, I figured it would have lasted longer. Anyway, as far as voltage drop, I'm looking at the meter on the instrument cluster, it drops from 14.5 v down to about 12 v when using power windows. Hopefully the recharged battery will correct my drain problem.

When you disconnected them did the test light go out?

OK, on the voltage drop. That meter is not very accurate. You should test it at the battery using a digital voltmeter. You may be able to improve that by cleaning the ground connection under the dash and the connections for the ground strap that runs from the intake manifold to the fire wall.

Good luck,