Unilite Module Woes

[Gray035]

The module in my Unilite distributor went out. That makes the second one in less than a year. I have the proper resistor installed and I haven't done any welding or anything. I did, however, recently upgrade to a single wire alternator. I learned in a series of searches that it's possible for a single wire alternator with a defective diode(s) to cause spikes in voltage when the key is turned off. Rather than buying yet another $100+ unilite module, I plan to install a pertronix replacement (the one that doesn't have an optical trigger like the unilite. The Pertronix, I hear, is more durable to power spikes. It's absurd to me that the Unilite isn't better designed to withstand them.

In any event, I think it's still worthwhile to troubleshoot the alternator to see if the diode(s) are indeed faulty. I don't know much about testing diodes, so I'm hoping there's someone here who can help. I set my multimeter on the diode test setting, and disconnected the battery. When I put the black lead on the case and the red lead on the charging (hot) terminal the multimeter steadily rises all the way to the multi meter's maximum reading (which is apparently a 1 on the far left of the display). When I reverse the leads the reading starts negative and then steadily rises until it reads approximately 400. I'm not sure what that means. My understanding was that the reading should be very low when the leads are reversed, but is 400 low? Perhaps I'm not doing something properly.

Can someone help?

[Lee]

Hi,

Sorry to hear of your problems.....

I have been running a Unilite for the past 17years without a single issue.. Last year I upgraded to the 1 wire alternator and .... so far so good. I even had a shop weld up some exhaust tubing on my truck with out disconnecting the Unilite without issue.

The best way to ohm out diodes is to remove them and then use the multi-meter..... should read very low resistance 1 polarity, then very high resistance reverse polarity. Heavy current diodes can be very hard to trouble-shoot with a multi-meter as the battery in the meter has trouble forward biasing the diode. I don't think it practical to de-solder diodes on these alternators as replacements can be picked up cheap in a Salvage yard.

Also, have you taken the alternator to an Auto-zone or O'Reilly for testing? It's free and should show if a diode issue exists during the load portion of the test.

When idling, are you getting steady ~14volts across the battery?

[Gray035]

I have not taken the alternator anywhere for testing. AS far as charging goes, it is working fantastically. Yes, I have a consistent 14+ volts across the battery terminals.

In the past 15 years or so I have gone through three modules on my Unilite. The first two times it would stop operating intermittently, generally the motor would shut off (like I turned off the key). This time it doesn't drop out (at least not yet) while driving. It stops working only when trying to re-start the truck. I know it's the module because when the truck won't start the credit card test shows the module not working. Then when the truck does start the credit card test shows the module as operative. It's really annoying when these things go out. They're expensive and also difficult to trouble shoot.

[Gray035]

I noticed something else today, but I have no idea whether it could be connected to my module problem. Seems like every time I've gotten in or out of the truck in the past couple weeks I've gotten sparked by what I believe is static electricity. It's been dry with santa ana winds here in SoCal. I wonder if enough static electricity could build up to impact the module in some way. If so, it seems like a pretty poor design by Unilite.

I'm going to install a pertronix unit this evening and see if that takes care of my issue.

[rollercam1]

Unalite's are very sensitive to backfeeding and grounds. I had several go bad due to that. I moved to MSD and haven't had any issues since

[Gray035]

Installed Pertronix module. Everything is going well so far.

[Lee]

Morning,

Glad you are up and running... please report back in a week or so with a "how goes it"

Lee

[Gray035]

The Pertronix module seems to have solved my problem. We'll see how long this module lasts and whether it is as sensitive as the MSD unit. These things are not cheap, and it's annoying to keep replacing them.

I am surprised that Mallory did not design a version that can withstand at least small fluctuations in voltage. These vehicles are fifty plus years old, and most of us working on them are not electrical engineers, so some voltage anomalies are to be expected right?