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Dodge Repair/98 Dodge 1500 ram: battery draining/IOD?


QUESTION: I check the drainage in the battery by using a test light. When I disconnect the radio the test light goes out. Bought a used radio and put it back in the pickup.  Tested for drainage and test light did not come on. Went back out and tried it again a few hours later and tested it again. The test light came on this time. Why is this happening?

ANSWER: Hi Ryan,
I don't understand what your 'test light' is supposed to measure: voltage presenced or just continuity (i.e. that current is flowing)? and what amount of voltage or current do you understand that the light indicates?
And can you tell me how you are connecting it to the battery?
What are you trying to learn with this measurement?
I should be able to help but I don't understand how or what you are measuring. And by the way, did the old radio work or not, and does the used radio work?

---------- FOLLOW-UP ----------

QUESTION: Sorry for not explaining things better. I'll try it again.  
My pickup will not start after sitting a couple of days.  I first thought it was my old battery, so I replaced it.  After a few weeks I noticed the battery was getting weak again.  So I went back to the place I bought the battery so they could check it. It was good. Next I started pulling fuses. I found that when my test light was hooked up in series and I pulled the iod fuse that the light goes off. I waited a few days and my battery was staying charged. So I figured the drain is coming from that circuit. I went through everything I could think of dome light, glove box, head light switch, air bag, ect. My friend said to check the radio because his pickup was draining because of the radio. So I pulled the radio out put my iod fuse in. Then hooked  upmy test light in series and the light stayed off. (When I bought the pickup brand new I had radio problems, the dealer would replace the radio because it would not turn on. My current radio still worked besides the CD player, CD player had not worked for a long time). Since the radio still powered up i really thought that wasnt the problem until my friend said to check it.  So today I decided to go to the junk yard to get a new radio. I bought one that is the same that came out of my pickup. I hooked it up and tested in seris and no light came on. I thought it was fixed. I went back and tried it again and the test light started blinking this time. I tried to use a volt meter but not sure I'm using it right or if I'm reading it right. I think I read 100 milliamp when I hooked it up in seris. This made me upset. I know there should be some power going to radio. I'm pretty sure I isolated the problem to the radio since when it is completely out of the pickup and I have no problems.  Tonight I'm going to hook it back up with my new radio and see what happens.  What would you check next?  Have you heard of this happening before?  Your first couple question I don't know.  It is just a regular test light, a cheap one to that. I'm trying to figure out why my battery keeps draining. All I know for sure is when I unhooked my radio my weak/dead battery went away.  My old radio worked but the CD player didn't. .  Everything works on the new radio.

I hope I explained everything.

Thanks Ryan

Hi Ryan,
I would not usually focus on the radio as the source of an ignition off draw/drain the battery problem because it requires very little current to maintain the radio presets. I would begin by attaching the volt-ohm-milliamp meter in place of the IOD fuse and see what the reading is when you choose the milliamp position of the selector. Usually the IOD is around 50 milliamps which means every day it sits unused that the circuit draw about 1 amp-hour of charge. You will notice that the battery storage capacity is usually humdreds of amp-hours so that is why it shouldn't drain even over 4 weeks of non-usage. Once you know the IOD current in milliamps you can then begin removing suspected items, one at a time to determing how much each is drawing by comparing the reading to when it was attached.
Be aware that if you turn on the ignition switch and then turn it off that several digital units will temporarily continue to draw for maybe a half-hour or so. So either wait for a while or in any case don't power up the vehicle before you start testing.
Unfortunately I don't have a Ram manual for the '90's so I can't tell you everything that draws off the IOD fuse(s) but you may be able to get that on-line from Autozone.
Please let me know what you learn.
Please 'rate' my answer  (see below).

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Roland Finston


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