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Radio briefly powers down when blower motor is on high

M

MNxj98

NAXJA Forum User
Location
Minnesota
98 xj 4.0 5 speed etc. having issues with the electrical system, I think. Not heavily modded, aftermarket jvc stereo, 2 amps and 2 12" subs, as well as aftermarket speakers front and rear.

When I turn the blower motor on (which needs fan speed resistor, so it runs on 4 only) the radio briefly powers down and the headlights flicker. I thought the alternator could have gone bad and I had a 136 amp waiting to be installed so I did that last night. No difference other than the volt guage seems a bit more happy. Checked fuses quickly (it's butt cold here) nothing seems blown but I plan on looking more next time I have it in the bosses heated garage as well as check/clean the grounds. Anything else I should be checking? Searched a bit and nothing came up. Any advice is greatly appreciated and I will try to check this as frequently as possible to give any other information you may need.
 
Aftermarket radio?

Did you wire it or did a shop?
 
Older jvc head unit was installed before I got it (4 years ago) and appears to have been done at a shop based on the connectors and general cleanliness of install. Subs were done by me like 3 years ago.


So the blower motor going bad is causing some crazy draw on the system then? Just curious but that would not suprise me one bit.
 
A common cause to resistors failing is the blower motor failing and pulling too much current thus toasting the resistor.

Is your wiring properly sized? You should be running a 4ga wire from the alternator. Preferably 2 or 1/0. Also, what about the power going to you amp. Is that an adequately sized wire? Are you running the hvac system on a defog mode? That will run the ac compressor which will dim the lights on my jeep a bit when it cycles on. I'm running upgraded 1/0 wire everywhere.

i would also be willing to bet that your motor to body ground at the firewall sucks. Also check the battery to block ground and see if that it in good shape. Bad grounds can have all sorts of negative effects.
 
The ground and wiring are all factory equipment but are on my list to be upgraded soon. The power wire for my amps is 2ga or better, I forget exactly. I'm not running any defog setting and the headlight don't just get dim they flicker.

Thanks for the advice so far everyone.
 
I would make the ground wires my priority. Should only cost a few bucks to get 3' or so of 1/0 fine strand. Look for some welding cable. That will be black and oil resistant usually. Next upgrade the charging cable off the alt. The stock 8ga is a little small for the stock alternator, let along the grand cherokee 136a alternator. You NEED a 2 ga or larger there. It is a short run so you won't build too much resistance, but a 1/0 would just smooth things out.

Either way, get some good grounding points first and see if that helps.
 
MNxj98 said:
Older jvc head unit was installed before I got it (4 years ago) and appears to have been done at a shop based on the connectors and general cleanliness of install. Subs were done by me like 3 years ago.


So the blower motor going bad is causing some crazy draw on the system then? Just curious but that would not suprise me one bit.
Click to expand...

One thing I noticed on my 98 is the shop that did the Po's stereo didn't ground it properly. It needs to be grounded to the dash, not to a wire in the harness. This resulted in my stereo flickering off sometimes
 
Yeah, grounds and charge wire will be the next thing I do.

For the ground wires and such, is there any "cable ends" or eyelets I should avoid or try to get? I'm assuming copper is my best bet.

@jeeperjohn so a capacitor inline with the actual head unit? Never heard that one before. Might check that out though.

@islanderoffroad I think I might have already changed the head unit ground to the way you are describing. Might have been my other truck though, same wiring harness so I forget which I did to which.
 
Blower motor is powered from the PDC fused with a 40A relay. Not sure exactly how much it draws on high when new but I can't imagine more than 30A. If you want to get an idea on it, put a multimeter in between the battery + terminal and the wire, then have a friend turn it on and make a mental note of the current draw.
 
Well guys, I am an idiot. I know I said it was butt cold here and it was even more cold today (sub zero temps) and what usually happens when it's cold? Bad batteries get even worse. Had to jump it this morning and after school. I'm surprised no one said "check your battery dummy!" Not sure why that wasn't my first thought either. Threw a new battery in it at work and all is well. Well all is better anyways. No more issues with the radio and whatnot.

Well anyways, I should be working on the suggestions above this weekend. Thanks again everyone. I really appreciate it.

I still feel like an idiot though!
 
So I'm going shopping for the main ground upgrade tonight or tomorrow and I could have sworn there was a DIY write up on it or at least a estimation on cable length. I'm pulling my hair out searching. If anyone knows its where abouts I would enjoy a link or a hint.
 
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